- Central Food Technological Research Institute

Transcription

HEAT TRANSFER STUDIES OF EQUIPMENTS
FOR PRODUCTION OF INDIAN TRADITIONAL
FOODS
A Thesis submitted to the
University of Mysore
for the award of degree of
DOCTOR OF PHILOSOPHY
in
Food Engineering
by
K. VENKATESH MURTHY
Department of Food Engineering,
Central Food Technological Research Institute,
Mysore 570 020, INDIA
February – 2006
K. Venkatesh Murthy
Scientist,
Department of Food Engineering,
Central Food Technological Research Institute,
Mysore-570 020, India
DECLARATION
I hereby declare that the thesis entitled “Heat Transfer Studies of
Equipments for Production of Indian Traditional Foods” which is
submitted herewith for the degree of Doctor of Philosophy in Food
Engineering of the University of Mysore, is the result of the research work
carried out by me in the Department of Food Engineering, Central Food
Technological Research Institute, Mysore, India under the guidance of
Dr. KSMS. Raghavarao, during the period 2001 to 2006.
I further declare that the results of this work have not been
previously submitted for any other degree or fellowship.
K. Venkatesh Murthy
Date:23.02.2006
Place: Mysore
CERTIFICATE
I hereby certify that this Ph.D thesis entitled “Heat Transfer
Studies of Equipments for Production of Indian Traditional Foods”
submitted by Mr. K.Venkatesh Murthy for the degree, Doctor of
Philosophy in Food Engineering of the University of Mysore, is the result
of the research work carried out by him in the Department of Food
Engineering, Central Food Technological Research Institute, Mysore,
under my guidance and supervision during the period 2001 to 2006.
(Dr. KSMS.Raghavarao)
Date:23.02.2006
Place: Mysore
ACKNOWLEDGEMENTS
I express my sincere gratitude to Central Food Technological
Research Institute Mysore and Council Scientific Industrial Research,
New Delhi for giving me an opportunity to continue higher studies.
I would like to express my sincere gratitude to my guide
Dr.KSMS.Raghavarao for his perseverance, persuasion, encouragement
and guidance during the course work.
I wish to express my deep sense of gratitude to Dr. V. Prakash,
Director CFTRI, Mysore for his constant encouragement and interest
shown in the field of equipment design for Indian Traditional Foods, which
would be a specialized and challenging area for engineers.
I express my thanks to Mr. A.Ramesh, Mr. H.Krishna Murty (former
HOD’s) and Dr. KSMS. Raghavarao, present Head of Food Engineering
for their support. I remember and thank Dr. R.Subramanian and Dr.
KSMS. Raghavarao, for their timely help during my professional career.
I gratefully acknowledge the help of staff of pilot plant Mr.
S.G.Jayaprakashan, Mr. I. Mahesh, Mr. B.V.Puttaraju, Mr. M.Shivakumar,
Mr. M.Nagaraju, Mr. K.Girish, Mr. Umesh, and Mr V.Kumar. Thanks are
also to my elder colleagues Mr R.Gururaj (Rtd), Mr. V.N.Subbarao (Rtd),
Mr. AVS.Urs (Rtd), Mr.D.Laksmaiah (Rtd), Mr. M.V.Srinivas Rao (Rtd),
Mr. Madhu (Rtd).
I also thank Ms. R.Chetana, Mr. Ganapathi Patil, and Mr. S.N.
Raghavendra for helping me during the preparation of this thesis.
I wish to thank my parents for providing me good education and
teaching me good values in life. I wish to thank my mother for giving me
blessings and guidance all these years that has lead to this humble work.
My mother was a silent crusader in shaping-up my personality.
My special thanks are also to my wife, Ms. Chetana who has
always been with me and thanks to my sons, Skanda and Sriram who
were all the while enquiring about the progress of the research work.
I thank and remember all my teachers who taught me good values
in life.
I remember my friend Mr. B.S. Prasad who has taught me to
accept success and failure in the same stride.
K.Venkatesh Murthy
Contents
Declaration by candidate
Certificate by guide
Acknowledgement
List of Figures
List of Tables
Notations
Synopsis
Chapter 1:
Introduction
1.1.0 History of Foods
1.2.0 Traditional Foods
1.3.0 Engineering Design of Machinery
1.4.0 Traditional Food Machinery
Chapter 2: Chapathi Machine
2.1.0 Introduction
2.2.0 Materials and Methods
2.2.1
Materials
2.2.2
Methods
2.2.3
Design of Machine
2.3.0 Results and Discussion
2.3.1
Design and Development
2.3.2
Standardization of Chapathi Dough
2.3.3
Heat Transfer Analysis
2.4.0 Conclusions
Chapter 3:
Dosa Machine
3.1.0 Introduction
3.2.1 Materials
3.2.2 Methods
3.2.3 Measurement of Thermal Properties
3.2.4 Design of Machine
3.3.1 Design and Development
3.3.2 Standardization of Dosa Batter
3.3.3 Heat Transfer Analysis
3.4.0 Conclusions
Chapter 4: Boondi Machine
4.1.0 Introduction
4.2.1 Materials
4.2.2 Methods
4.2.3 Measurement of Thermal Properties
4.2.4 Design of Machine
4.3.1 Design and Development
4.3.2 Standardization of Chickpea Batter
4.3.3 Heat Transfer Analysis
4.4.0 Conclusions
Chapter 5: Conclusion and Suggestion for Future Work
References
Annexure 1
Annexure 2
List of Figures
1.1
Versatile Grating Machine
1.2
Hot air Popping Machine
1.3
Bio – Plate Forming Machine
1.4
Integrated Hot Air Roasting Machine
1.5
Continuous Lemon Cutting Machine
2.1
Chapathi Machine
2.2
Chapathi Sheeting Unit
2.3
Pneumatic Extruder
2.4
Improved Pneumatic Extruder
2.5
Dusting and Cutting Device
2.6
Chapathi Baking Unit
3.1
Experimental Set-up for Measuring Thermal Diffusivity
3.2
Graph indicating the increase in Wall Temperature and
Center Temperature of the Copper Cylinder (Dosa
Batter)
3.3
Dosa Machine
3.4
Improved Dosa Machine
3.5
Auto Discharge Assembly
3.6
Floating spreader Assembly
3.7
Floating Scraper Assembly
3.8
Improved Batter/Oil Dispenser
3.9
Microstructure of Dosa Prepared on Different Hot Plate
Materials
3.10
Profilogram of Dosa Made Using Dosa Machine
4.1
Boondi Machine
4.2
Experimental Set-up for Measuring Thermal Diffusivity
4.3
Graph indicating the increase in Wall Temperature and
Center Temperature of the Copper Cylinder Chickpea
batter
4.4
Circular Deep Fat Fryer
4.5
Discharge Mechanism
4.6
Improved Circular Deep Fat Fryer
4.7
Improved Discharge Mechanism
4.8
3D Graph Showing the Influence of Die Plate Diameter
on Moisture Content in Batter and Colour Change in
Boondi
4.9
3D Graph Showing the Influence of Die Plate Diameter
on Moisture Content in Batter and Texture (crispness) of
Boondi
4.10
Contour Plots Showing the Influence of Die Hole
Diameter and Total Colour
List of Tables
2.1
Chemical and Rheological Characteristics of Flour Samples
2.2
Effect of Water and Optional Ingredients on the Rheological
Characteristics of Chapathi Dough
2.3
Effect of Slit Width on the Thickness of Chapathi Sheet
2.4
Effect of Water and Optional Ingredients on the Sheeting
Characteristics of Chapathi Dough
2.5
Effect of Water and Optional Ingredients on the Quality of
Chapathi
2.6
Comparative Quality Characteristics of Chapathi Made by
Manual and Mechanical Sheeting
2.7
Average Thermal Conductivity (kc) as a Function of Hot
Plate Temperature of Whole Wheat Flour
2.8
Average Thermal Conductivity (kc) as a Function of Hot
Plate Temperature of Atta
2.9
Complete Heat Balance on the Chapathi Baking Oven
2.10 Estimation of Thermal Efficiency of the Chapathi Baking
Oven
3.1
Wall and Center Temperature of the Copper Tube for Dosa
Batter
3.2
Composition of Rice and Black gram
3.3
Estimation of Thermal Properties of Instant Dosa Batter
3.4
Comparison of Thermal properties of Dosa Batter by
Composition and Experimentation
3.5
Estimation of Thermal Efficiency of the Dosa Machine
3.6
Expansion Characteristic of Rice and Urdh Dhal During
Soaking
3.7
Effect of Temperature on Quality of Fermented Dosa Batter
3.8
Effect of Ingredients on Quality of Dosa Using Conventional
Batter
3.9
Average Thermal Conductivity (kd) as a Function of Hot
Plate Temperature
3.10 Average Radiative Heat Transfer Coefficient (εpd) as a
Function of Refractory Surface Temperature
3.11 Complete Heat Balance on the Dosa Machine
4.1
Coded and Uncoded Process Variables and their Levels for
Boondi
4.2
Wall and Center Temperature of the Copper Tube
For Chickpea batter
4.3
Composition of Chickpea
4.4
Estimation of Thermal Properties of Chickpea Batter
4.5
Comparison of Thermal properties of Chickpea Batter by
Experimentation and Composition
4.6
Complete Heat Balance on the Deep Fat Frying of Boondi
4.7
Sphericity of Boondi Globules
4.8
Central
Composite
Rotatable
Design
and
Response
Functions
4.9
Analysis of Variance (ANOVA) for fit Second Order
Polynomial Model and Lack of fit for Total Colour Difference
and Compressive Strength as per CCRD
4.10 Experimental and Predicted Values of Compression at
Optimized Frying Conditions
4.11 Estimated Co-efficient for Polynomial Fit representing
Relationship between Response and Process Variables
4.12 Average Convective Heat Transfer Co-efficient (ho) as a
Function of Hot Oil Temperature of Boondi Globule
Notations
σ
Stefan-Boltzman constant, (W/m2. h. K4)
εHc
Emissivity of the hood of Chapathi baking oven
εHd
Emissivity of the hood of Dosa machine
εpc
Emissivity of the Chapathi
εpd
Emissivity of the Dosa
Δtc
Chapathi baking time, (h)
Δtd
Dosa baking time, (h)
λv
Latent heat of water evaporation, (kJ/kg )
A
Constant rate of temperature rise of batter, (°C/min)
Ac
Area of the Chapathi bottom in contact with the hot plate, (m2)
Ad
Area of the Dosa in contact with the hot plate bottom, (m2)
Arc
Area of the radiating refractory surface of Chapathi baking
oven, (m2)
Ard
Area of the radiating refractory surface of Dosa machine, (m2)
Cpb
Specific heat of Chickpea batter, (kJ/kg. °K)
Cpc
Average specific heat of wheat flour, (kJ/kg. ° K)
Cpd
Specific heat of Dosa batter, (kJ/kg. °K)
Dc
Diameter of Chapathi, (m)
Dd
Diameter of Dosa, (m)
Df
Degree of freedom
fprc
Geometrical factor for Chapathi
Fprc
Overall coefficient for radiation heat transfer
fprd
Geometrical factor for Dosa
Fprd
Overall coefficient for radiation heat transfer
hFc
Convective heat transfer coefficient of Chapathi, (W/m2. oK)
hFd
Convective heat transfer coefficient of Dosa, (W/m2. oK)
ho
Convective Heat transfer co-efficient of groundnut oil,
(W/m2 °C)
kb
Thermal conductivity of Chickpea batter, (W/m.°C)
kc
Thermal conductivity of the Chapathi, (W/m.°C)
kd
Thermal conductivity of Dosa, (W/m.°C)
Kdb
Thermal conductivity of Dosa batter, (W/m. °C)
L
Moisture loss during baking, (kg)
ma
Mass fraction of ash
mc
Mass fraction of carbohydrate
mf
Mass fraction of fat
mm
Mass fraction of moisture
mp
Mass fraction of protein
Q1
Calorific value of LPG, (kJ/Kg)
Q2b
Sensible heat absorbed by Boondi, (W)
Q2c
Sensible heat absorbed by Chapathi, (W)
Q2d
Sensible heat absorbed by Dosa, (W)
Q3b
Latent heat absorbed by Boondi, (W)
Q3c
Latent heat absorbed by Chapathi, (W)
Q3d
Latent heat absorbed by Dosa, (W)
QAb
Total theoretical heat absorbed by Boondi, (W)
QAc
Total theoretical heat absorbed by Chapathi, (W)
QAd
Total theoretical heat absorbed by Dosa, (W)
QTb
Total heat absorbed by Boondi, (W)
QTc
Total heat transferred to Chapathi, (W)
QTd
Total heat transferred to the Dosa, (W)
q1d
Heat lost by the water bath, (W)
q2d
Heat gained by batter,(W)
qcc
Heat transferred by conduction to Chapathi, (kJ)
qcd
Heat transferred by conduction to Dosa,(kJ)
qFc
Heat transferred by convection to Chapathi, (kJ)
qFd
Heat transferred by convection to Dosa , (kJ)
qRc
Heat transferred by radiation to the Chapathi, (kJ)
qRd
Heat transferred by radiation to Dosa, (kJ)
r
Radius of Boondi Globule, (m)
R
Radius of the copper cylinder, (m)
T1
Out side surface temperature of the copper cylinder, (°C )
T2
Temperature of batter inside the copper tube, (°C )
T3
Surface temperature of Boondi globule, (°C )
T4
Core temperature of Boondi globule, (kg)
T5
Temperature of groundnut oil, (°C )
Tc
Temperature of Chapathi, (°C )
Tcb
Chapathi bottom surface temperature, (°C )
Tcd
Wheat flour/dough temperature, (°C )
Tct
Temperature of the Chapathi top surface, (°C )
Td
Measured temperature of the Dosa, (°C )
Tdb
Temperature of the Dosa bottom surface, (°C )
Tdd
Temperature of Dosa batter at ambient conditions, (°C )
Tdt
Temperature of the Dosa top surface, (°C )
THc
Hood (refractory surface) temperature of Chapathi baking
oven, (°C )
THd
Hood (refractory surface) temperature of Dosa machine, (°C )
Tp
Hot plate temperature, (°C )
Tp1
Predicted temperature of the Dosa, (°C )
TRc
Temperature of the hot air inside the hood, in (°C )
TRd
Temperature of the hot air inside the hood, (°C )
W1
Mass of Chapathi dough, (kg)
W1d
Mass of Dosa, (kg)
Wc
Mass of Chapathi dough, (kg)
Wd
Mass of Dosa batter, (kg)
xc
Thickness of the Chapathi, (m)
xd
Thickness of the Dosa, (m)
αb
Thermal diffusivity of Chickpea batter, (m2/s)
αc
Thermal diffusivity of Chapathi dough, (m2/s)
αd
Thermal diffusivity of Dosa batter, (m2/s)
Θ
Duration of Experiment, (Min)
ρb
Density of Chickpea batter, (kg/m3)
ρd
Density of Dosa batter, (kg/m3)
DBNU
Dark brown non-uniform
BU
Brebanders unit
DGNU
Dull grey non-uniform for Chapathi baking oven
LBU
Light brown uniform
SEM
Standard Error Mean
NS
Not significant
Synopsis
The traditional foods have been prepared for hundreds of years
and the art of preparation has been perfected over years and varied
across the country. The attempts to change these food habits have not
been successful to the extent envisaged. As the value of time is
increasing day by day, especially with the working women being the sign
of times, the demand for the ready-to-eat traditional foods is also
increasing. Though the basic kitchen technology for the production of
these foods is known, considerable research and development efforts are
required to translate these technologies to the level of large-scale
production. This requires a lot of input from the food engineers and
technologists. The variation in these foods is so vast that it is very difficult
to treat them under a uniform class. The traditional food prepared and
consumed in one region may not be known in another region. Till recently,
the preparation of traditional foods was considered more an art than
science and the mechanization has been thought of very recently.
The successful operation of any machine depends largely on the
kinematics of the machines. The motion of parts is largely of rectilinear
and curvilinear type. Rectilinear type includes unidirectional, reciprocating
motion while curvilinear type includes rotary, oscillatory and simple
harmonic motions. Design is a process of prescribing the sizes, shapes,
material composition and arrangements of parts so that the resulting
machine will perform the prescribed task. The role of science in the
design process is to provide tools, to be used by the designers as they
practice their art. It is the process of evaluating the various interacting
i
alternatives that designers need for a large collection of mathematical and
scientific tools. These tools when applied properly can provide more
accurate and reliable information for use in judging a design, than one can
achieve through the process of iteration. Thus mathematical and scientific
tools can be of tremendous help in deciding alternatives. However,
scientific tools aid imagination and creative abilities of the designers to
make faster decisions. The largest collection of scientific methods at the
designer’s disposal falls into the category of analysis. These are the
techniques, which allow the designer to critically examine an already
existing or proposed design in order to judge its suitability for the task.
Thus analysis in itself is not a creative science but one of evaluation and
rating things that are already conceived. Most of the effort is spent on
analysis but the real goal is the synthesis, that is, the design of a machine
or system. However, analysis is a vital tool, inevitably be used as one of
the steps in the design process.
With this in view, development of equipment such as continuous
Chapathi machine automatic Dosa machine and continuous circular deep
fat fryer for Boondi along with the integration of mechanization with the
technological standardization of respective dough/batters is considered in
the present study.
The subject matter of this thesis is presented in five chapters.
Chapter 1: This chapter comprises of general Introduction and scope of
the present investigation, literature review pertaining to the design
ii
fundamentals and design considerations for food processing machines.
Further, the gist of 5000 years history of Indian traditional foods, the need
for mechanization with respect to the present day context and the
objectives of the present study have been presented.
Chapter 2:
It comprises of the preamble for Chapathi machine. The
optimization of the moisture content for different wheat flours such as
whole-wheat flour, resultant atta, mixing time and resting time of the
dough are presented and the rheological properties of dough, the
optimum thickness of the Chapathi sheet for machining, the effect of
dusting on the quality of the sheeting are discussed. Engineering and
thermal properties such as shear strength of Chapathi sheet and thermal
conductivity, specific heat, thermal diffusivity of the Chapathi dough are
presented. This chapter presents the approach in understanding and
integrating the thermal and engineering aspects of the Chapathi machine.
The conceptual schematic, the engineering details of machine and the
selection of the engineering materials for different parts are presented.
The working principle of the integrated Chapathi-making machine,
namely, pneumatic sheeting, dusting and cutting devices coupled to the
baking oven are discussed. The conceptual designs of different parts
such as baking oven, custom-built burner are discussed. The energy
balance in order to arrive at the theoretical heat required for the baking of
Chapathi, the residence/baking time based on added moisture and the
heat loss in baking oven, design of the gas burner, air fuel ratio required
for complete combustion of the liquid petroleum gas are also discussed.
iii
The rate of heat transfer and total heat requirement for baking of the
Chapathi is presented. The contribution of different modes of heat transfer
and its relevance to the sensory characteristics of baking Chapathi,
thermal efficiency of the baking oven for Chapathi are discussed.
Chapter 3: This chapter comprises of general introduction of Dosa, an
Indian traditional break-fast food and conceptual design of automatic
Dosa machine. Different parameters essential for the preparation of the
Dosa batter such as soaking time, swelling ratio, moisture uptake during
soaking, final moisture content in batter, mixing and fermentation time are
discussed. The results of this chapter are useful in understanding the
integration of technological and engineering requirements of the
automatic Dosa machine. The Dosa batter was studied under two
categories, namely, conventional batter and instant batter mix (powder).
The optimization of different ingredients for the preparation of the Dosa
batter, effect of added moisture on baking time and product quality are
presented. The rheological properties of the conventional batter as well as
instant Dosa batter in terms of the viscosity at different moisture levels
with the effect on the final product quality, scanning electron microscopic
study to examine the pattern of evaporation of moisture during baking has
been presented. The thermal properties such as specific heat, thermal
conductivity and thermal diffusivity of the Dosa batter are presented. This
section presents the approaches that are useful in calculating the
theoretical heat requirement of the automatic Dosa machine and in turn
design of the circular burner. Trained panelists from sensory science
iv
department of CFTRI evaluated the product prepared using the automatic
Dosa-machine. The product prepared from both conventional and instant
batters are evaluated by the panelists for various attributes for the
sensory evaluation of the product and the results are presented in this
section. The results of this chapter are useful in understanding the market
acceptability of the machine made product.
The principle of operation and salient features of the automatic
Dosa-machine are discussed. The heat transfer study across the hot plate
of the machine, the quality parameters of the product produced using hot
plates of different materials such as stainless steel, cast-iron, alloy steel
and teflon coated aluminum and the microstructure along with the sensory
aspects of the product produced using these hot plates have been
discussed. The Dosa machine has a circular burner for supply of heat to
the hot plate, which is designed to be concentric to the circular hot plate.
Based on the theoretical heat estimate, including the operational losses,
the dimensions of the burner, number as well as diameter of the holes
and the size of the mixing tube along with the required air fuel ratio are
presented. The scraper is an important sub-assembly in the automatic
Dosa-machine. It is a straight edged strip of stainless steel, which rests on
the rotating hot plate. The curvilinear motion of the hot plate against a
straight edge will aid in scraping the Dosa from the hot plate and also roll
the product into a presentable form. A circular scraper, which is an
improvement over the straight edged scraper, not only scrapes and rolls
the product but also discharges the product from the hot plate in to the
collection chute is presented in this section. The heat transfer studies and
v
analysis of different modes of heat transfer, their individual contribution
towards the product quality, theoretical heat requirement, thermal
efficiency and sensorial properties of the product are presented. Based on
the heat transfer studies, which clearly indicated mode of heat transfer to
be more important than the quantum of heat transferred and accordingly,
the design modifications are incorporated in the machine. Baking
temperature, baking time, sensorial attributes, textural properties of the
product such as colour, shear strength are discussed in this chapter.
Chapter 4: This chapter comprises of general introduction of Boondi, (as
a snack food) conceptual design of continuous forming device and
continuous circular deep fat fryer. Different ingredients essential for the
Chickpea batter, final moisture content in the batter and the mixing time
are also discussed. The results of this chapter are useful in integrating the
engineering and thermal aspects of the continuous forming device and
continuous circular deep fat fryer. Optimization of different ingredients for
the preparation of Chickpea batter, effect of added moisture on frying
time, diameter of the forming die, height of fall of the globule from the
forming die to the top of the oil bath and product quality are presented.
The rheological properties of the Chickpea batter, with varied added
moisture, in terms of the viscosity and their effect on the final product
quality has been presented. The thermal properties such as specific heat,
thermal conductivity and thermal diffusivity of the Chickpea batter are
presented. Calculation of the theoretical heat requirement of the
continuous circular deep fat fryer and its application in design of the
vi
circular burner are also discussed. The product prepared from the
Chickpea batter was evaluated for various attributes of the sensory
evaluation of the product and their observations are presented in this
section. The results of this chapter are useful in understanding the
integration of the technological and mechanization of the process besides
the market acceptability of the machine made product.
The principle of operation and salient features of the forming and
frying machine are also discussed. The conceptual design for continuous
forming device and continuous circular deep fat fryer having different
parts such as the forming sub-assembly, discharge mechanism for the
fried product; custom built circular burner etc are discussed. The
theoretical heat required for frying of Boondi, the residence/frying time
based on added moisture and the heat loss in the frying machine are
discussed. The continuous circular deep fat fryer has been designed with
a circular burner for supply of heat to the oil, which is concentric to the
circular trough. Based on the theoretical heat analysis including the
operational losses, the dimensions of the burner, the number and
diameter of the holes, size of the mixing tube along with the required air
fuel ratio are arrived at. The discharge mechanism is an important subassembly in the continuous circular deep fat fryer. The discharge
mechanism has to work inside a circular rotating trough picking up the
fried product from the hot oil bath while draining the excess oil. The heat
transfer studies of the continuous circular deep fat fryer is presented in
this section. The theoretical heat analysis, thermal efficiency and
sensorial properties of the product are also presented. The frying
vii
temperature, frying time and textural properties of the product such as
colour, shear strength and sensorial attributes are also discussed in this
chapter.
Chapter 5: This chapter contains the conclusions of the work
carried out during the development of the different machinery for Indian
traditional foods. It also highlights the importance and scope in design and
development of machinery for diverse Indian traditional foods, which can
be a specialized area of research for future work.
viii
Section 1.1.0: History of Foods
Over the last few hundred centuries, the glacial ages have
alternated with warm epochs. Following the last warm period, about
15,000 years ago, man came to his own, starting off as a food gatherer
and then gradually evolving as a food cultivator. During this long phase
fruits appeared to be his main dietary item. The development of
agriculture after about 10,000 BC rapidly changed the dependence on
constant hunting for animal food (Achaya, 1994). In the course of a few
millennia meat declined even further, and the agricultural/horticultural
produce started to dominate the diet. At every place around the world
where human evolved, a similar evolutionary pattern has characterized
the kind of food that he/she consumed. This can be deduced from the
evidence that was left behind by way of tools, cave paintings, and
surviving words.
Every community that lived in India has a distinctive food ethos.
Most of these, however, have been influenced by Aryan beliefs and
practices. Originally starting from the North and North-West of India,
Aryan ideas gradually expanded all over the country, sub-suming earlier
practices and exerting a strong influence on those cultural beliefs that
appeared later.
Food for Aryan belief was not simply a means of bodily
sustenance; it was part of cosmic moral cycle and Bhagavadgita says,
“From food do all creatures come into being”. In the great Aryan cosmic
1
cycle, the eater and the food he eats and the universe must all be in
harmony and all of these are different manifestations of same essence.
The domestic hearth in a Hindu home was considered an area of
high purity; even of sanctity, in fact, it was set up adjacent to the area of
worship. The domestic hearth had to be located far away from wastedisposal area of all kinds and demarcated from sitting, sleeping and visitor
receiving areas (Achaya, 1994). Before entering the cooking area, the
cook was to take bath and don unstitched washed clothes. The objective
of cooking is not simply to produce materials suitable for eating but to
conjoin the cultural properties of the food with those of the eater.
Section 1.2.0: Traditional Foods
Indian traditional foods have a long history and the knowledge of
preparing them has been passed on from generation to generation.
Efforts have been made to document this vast knowledge, which is in the
domain of a few families/individuals. Large number of traditional foods are
being consumed by people in different geographical locations in the
country. Indian sweets and snack food industry are on the threshold of
revolution and identified to have good export potential. Central Food
Technological Research Institute (CFTRI), Mysore has made a significant
contribution in this context towards the process development and
mechanization.
2
1. Chapathi
A variety of breads have been developed from wheat, which is the
main staple food in India. The term bread is hardly appropriate for a
numerous roasted, fried and baked items of India. Dry baked forms of Roti
include the common Chapathi, baked dry on a hot plate (thava), some
times puffed out to a Pulka by brief contact with live coal/flame. A very
thin Chapathi prepared in Gujarat state is the Rotlee. The Rumali Roti
(scarf) is also thin but much bigger in size. The Bhatia made in the state
of Rajastan, are soft, thin Roties that come apart as two circles because
of the style of rolling of the dough. Dough carrying spinach yield distinctive
Roties, the Missiroti, baked dry on a thava, flaky in texture, has spinach,
green chillies and onions in the dough. The Kakras are kneaded with milk
and water and are crisp products that keep well for longer periods and are
carried by Gujarathi travelers.
Wheat products after rolling out can be either pan baked using just
a little fat, or baked with out fat. Paratas are the most common, often
square or triangular in shape rather than circular. The dough can be
mixed with seasoned vegetable like potatoes, spinach or methi and these
products are eaten with curds. Poories are deep fried products made from
wheat flour and some times the dough is mixed with sugar or fat. The
dough of the Bhatura is allowed to ferment using yogurt, and then rolled
out to give a layery fried product (Achaya, 1994).
The other category of the wheat based product which are
unleavened and baked, either in closed or heated oven or in Indian style
3
tandoors, which are open, lined, glowing ovens with live coals placed at
the bottom. Naan is made of maida, the white inner flour of wheat, which
is leavened before baking to yield a thick elastic product. Naan is normally
dressed with either saffron water or tomato to give red surface colour after
baking.
2. Dosa
Food was delicious and varied in South India in the first few
centuries AD. Rice was converted into many appetizing foods. The appam
was a pancake baked on a concave circular clay vessel and a favored
food soaked in milk. The other forms of shallow pan-baked snack were
Dosai and adai, both based on rice. The Dosa is now made by fermented
batter, a mixture of ground rice and urdh dhal and the adai is made from a
mixture of almost equal parts of rice and four pulses, ground together
before shallow baking.
The tosai (Dosai) is first noted in the Tamil Sangam literature of
about 6th century AD. It was then perhaps, a pure rice product, shallowfried in a pan, while the appam of similar vintage was heated without fat
on a shallow clay chatti (pan). Today the Dosa is made from fermented
batter and Dosa of Tamil Nadu is soft, thick product, while that of
Karnataka is thin, crisp and large. It is frequently stuffed with a spiced
potato mash to yield the popular masala-Dosai.
4
3. Idli
In Tamil literature the ittali is first mentioned only as early as the
Maghapuranam of the 17th century AD. The Manasollasa of about 1130
AD written in Sanskrit describes the Iddarika as made of fine urad flour,
fashioned into small balls, fried in ghee and then spiced with pepper
powder, jeera powder and asafetida. In Karnataka, the Idli in 1234 AD is
described as being `light, like coins of high value’, which is not suggestive
of a rice base. The steaming vessel in Kannada is allage, and the iddalig’.
In all these references, three elements of the modern Idli are missing.
One is the use of rice grits (in the proportion of two parts to one of urad).
The next is the long process of grinding and the overnight fermentation of
the ground batter. The last is the steaming of the fermented batter. The
literature does not offer certain answers as to when in the last few
centuries these elements entered the picture.
In 1485 AD and 1600 AD, the Idli is compared to the moon, which
might suggest that rice was in use; yet there are references to other
moon-like products made only from urad flour. The Indonesians ferment
many materials (soyabeans, groundnuts and fish) have a similar
fermented and steamed item called kedli. Steaming is a very ancient form
of food preparation in the Chinese ethos, referred to by Xuan Zang saying
that in the 7th century AD India did not have a steaming vessel. It has
been suggested that the cooks who accompanied the Hindu kings of
Indonesia during their visits home (often enough looking for brides) during
the 8th to 12th centuries AD, brought fermentation techniques with them to
5
their homeland. Perhaps the use of rice along with the pulse was
necessary as a source of mixed natural microflora needed for an effective
fermentation. Yeasts have enzymes which break down starch to simpler
sugar forms and bacteria which dominate the Idli fermentation carry
enzymes for souring and leavening through carbon dioxide production.
Even Czechoslovakia has a similar steamed product called the Knedlik
(pronounced needleck). Steaming can of course be achieved by very
simple means, merely by tying a thin cloth over the mouth of a vessel in
which water is boiled and its antiquity would be impossible to establish. It
is not unlikely that the name of the Idli persisted even though its character
changed with time, resulting in diversified forms of “Idly” (Achaya, 1994).
Section: 1.3.0: Engineering Design of Machinery
Designing process requires an organized synthesis of known
factors and the application of creative thinking. Design and production, the
two principal areas of technical creativity are closely interrelated. The
designer has to keep in mind, the product designed to be manufactured in
the most economical way. Apart from the knowledge in manufacturing
aspects, he/she must be in touch with the consumer needs to design the
machine to suit their requirement. Regulations, national codes, safety
norms are to be given due consideration and these often play a decisive
role in determining the final design.
The machine design can be broadly classified into three categories
as adaptive design, developmental design and new design. In adaptive
design the designer is concerned with the adaptation of the existing
6
design. Such design does not demand special knowledge or skill and the
problems can be solved with ordinary technical training. A beginner can
learn a lot from the adaptive design and can tackle tasks requiring original
thoughts. A high standard of design ability is needed when it is desired to
modify a proven existing design in order to suit a different method of
manufacture or to use a new material. In developmental design, a
designer starts from an existing design but the final result may differ quite
remarkably from the initial product. This design calls for considerable
scientific training and design ability. New design, (which never existed
before) is done by dedicated designers who have sufficient personal
qualities of high order. Research, experimental activity and creativity is
aptly required.
In the actual design work in industries one need not design the
simple elements like bolt or nut every time and most of these elements
are readily available to meet standard specifications. A designer is
required to select these elements properly and put them together to meet
the requirements and this process of selection of elements and their
configuration is usually termed as system design. It is usual to break
down the complete system into a series of sub-assemblies, components
and materials and these sub-assemblies can be further broken down to
single detail parts each of which is made from raw material. In system
design, a designer has to properly think of a device capable of giving
required output for a given input; devise means and obtain the emergent
properties of the elements and system and their configuration; study the
feasibility of elements and system; examine the compatibility and
7
interconnection of elements and system; and find the optimized design or
select the best system. System design means design of complex system
comprising of several elements. It should always be remembered that
requirement for a design concern demand, function, appearance and cost.
It is known that every process is a combination of three elements,
namely, the man, machine and material. A change in any one of these will
result in a change in the process. All these three elements are subjected
to inherent and characteristic variations. These variables result in the
variation in size of components. Due to inevitable inaccuracy of
manufacturing methods, it is not possible to make any part precisely to a
given dimension and it can only be made to lie between maximum and
minimum limits. The difference between these two limits is called the
permissible tolerance. The tolerance on any component should be neither
restrictive nor permissive and should be as wide as the process demands.
Generally in engineering, any component manufactured is required to fit
or match with some other component. The correct and prolonged
functioning of the two components matched (assembled parts) depends
up on the correct size and relationship between the two. Thus by variation
of hole and shaft sizes, innumerable types of fits can be possible. The
limits and fits provide guidance to the user in selecting basic functional
clearances and interferences for a given application or type of fit and in
providing tolerances which provide a reasonable and economical balance
between, fits, consistency and cost.
8
Section 1.4.0: Traditional Food Machinery
The popularization of traditional foods is gaining momentum and is
becoming very popular. The increasing consumer demand for high quality
and safe product at affordable price has resulted in a need for
mechanization, in which the food engineers and technologists have a
major role. The mechanization and automation of traditional foods offers a
challenge as many parameters affect the product quality. The trend
towards the urbanization with a concomitant scarcity of domestic help,
increasing trend in the employment of housewives outside their homes to
supplement the income have increased the demand for ready or
processed foods. The vast variations in the Indian traditional foods made
it difficult to mechanize and also to design a single cost effective machine
to manufacture different types of foods. Some of the food processing
machinery designed at Central Food Technological Research Institute,
Mysore are described below.
1. Chapathi machine
The Chapathi machine comprises of two major sub-units, namely
the Chapathi sheeting unit and the Chapathi-baking unit. Both these units
are integrated into the Chapathi machine in order to produce Chapathi
continuously in largescale automatically. The forming of circular Chapathi
discs of required thickness and diameter is done using the sheeting unit
and the discs are transferred to the Chapathi-baking unit for baking. The
development of the Chapathi machine design includes series
9
of improvements and is presented as improved devices. The invention is
covered by Indian patents.
2. Dosa Machine
Some traditional Indian foods such as Dosa and Idli are becoming
more popular. Dosa, an Indian traditional food is consumed by a large
section of population as a breakfast food. For the largescale production, a
continuous automatic Dosa machine was designed and fabricated. The
machine can handle different types of batter such as conventional batter
as well as instant batter mix (powder). The consistency of the batter, the
time–temperature for baking of the Dosa have been standardized.
Predetermined quantity of the batter is dispensed, spread to uniform
thickness on the hot plate of the machine and baked Dosa are scraped,
rolled and discharged automatically. The invention is covered by Indian
patents.
3. Boondi Machine
The Boondi machine has two sub-units, namely, Boondi forming
unit and Boondi frying unit and both are integrated for continuous
operation. The forming machine has a die, for varying the diameter of the
globules and the unit has the provision for changing the die plates having
different sizes of holes. In order to form Boondi globules, the batter is
made to flow through perforated die under mechanical vibration. As the
batter passes through the holes/perforations of the die, it breaks into
10
globules, fall directly into the hot oil of the continuous circular fryer. The
invention is covered by Indian patents.
4. Versatile Grating Machine
Grating machine is useful for large-scale preparation of gratings of
uniform dimension of fruits, vegetables and coconut (shown in Fig. 1.1).
The gratings obtained using this machine will have application in fruit,
vegetable, coconut and other similar food processing industry. Based on
stationery circular multi pointed cutter, rotating vanes and conical rotor
concept, a device can grate different varieties and sizes of fruits and
vegetables of different geometry and hardness. Raw mango, Carrot,
Amla, Copra (dried), Beet root etc. are a few common types of fruits and
vegetables which are grated using this machine. The invention is covered
by an Indian patent.
5. Hot Air Popping Machine
The hot air popping machine is designed for popping of maize,
paddy, and sorghum. The unit consists of a fluidization chamber, a screw
conveyor for feeding the material into the combustion chamber for
popping and a discharge chute (shown in Fig. 1.2). The popped material
due to the decrease in bulk density (increase in volume) is discharged
through the discharge chute. The startup (heat up) and shutdown times of
the popping are rather instantaneous and the hot air is recirculated. The
direct heat transfer to heating medium (air) and recirculation of hot air
11
increases the thermal efficiency of the popping machine. The invention is
covered by an Indian patent.
6. Bio–Plate Forming Machine
Traditionally plant residues such as leaves, areca palm sheath
have been used in India for forming into different shapes such as plates,
cups, saucers etc. for serving of foods. Leaves of plants such as of Butea
or Bauhunia are washed, softened and depending on the desired size of
plate, two or more of the leaves are manually stitched together at the
edges, using small sharp pins made of twigs or coconut ribs. Traditionally,
cups and saucers of this nature are also used for vending of butter and
other semi-solid materials. In its construction, the bio-plate forming
machine (shown in Fig. 1.3) consists of a prime mover for the rotary
motion of the die sets, a set of punch and die, an actuating cam, a main
frame and electrical parts. The forming of bio-plate is by the process of
thermosetting of the leaves and axial thrust with heat is applied through
the punch and die set. The invention is covered by an Indian patent.
7. Integrated Hot Air Roasting Machine
Roasting is a high temperature short time heat treatment operation
and is done to enhance the organoleptic properties of food materials. The
roasting, resting and cooling decks are incorporated in a single machine
so that the three operations are done sequentially. The integrated hot air
roasting machine (shown in Fig. 1.4) was employed for roasting/toasting
of cereals, pulses, spices, oil seeds and ready to-eat snack foods using
12
flue gas. The product processed by using this device has uniform color,
moisture and other sensorial properties. The material is processed under
hygienic conditions in a continuous manner. All the variables such as
residence time, temperature of the hot air, resting time and cooling time of
the roasted material are done sequentially using a programmable logical
controller (PLC).
The device is energy efficient as the hot air is
recirculated. The invention is covered by an Indian patent.
8. Continuous Lemon Cutting Machine
The machine relates to a continuous circular cutting machine for
lemon and other similar spherical fruits. The lemon-cutting machine
(shown in Fig. 1.5) is capable of cutting the spherical fruits either into two
halves or into four equal parts. Cut lemon and other similar fruits will have
application in pickle and other similar food processing industry. The
machine design is based on the concept of stationery cutter and rotating
locating rollers. The invention is covered by an Indian patent.
Although design and development of these machinery has been
carried out over the years at CFTRI, the traditional food machinery
considered for detailed study in the thesis are,
1. Chapathi machine.
2. Dosa machine.
3. Boondi machine
13
The study is broadly classified into two categories, namely, i)
Design of machinery and technology of preparation of traditional foods
and ii) integration of the two.
The technology aspect of the study involves standardization of
relevant food materials to meet the requirement of the machines and
study of their thermal properties for the completeness of the design of
these machines. Several Indian patents extensively cover the above
inventions (Venkateshmurthy et al., 1997, 2000, 2001, 2002, and 2005).
The theoretical studies carried out were of immense use in
improving the design of these machines to achieve near perfection. Many
a time the machines were modified to suit the food material and the food
formulations were modified to adapt to the engineering design. The
process of iteration helped in matching the machine to food and food to
machine and finally resulting in a good match.
14
Schematic of Machine Development
Food processing machinery
Technology of Food
Food machinery
Thermo physical properties
Processing
Physical properties
Conceptual schematic
Thermal properties
Thermal Diffusivity
Standardization of Ingredients
Engineering Design
Thermal conductivity
Specific heat
Standardization of preparatory
operations
Energy / Heat requirement
FOOD PROCESSING MACHINE
Fabrication
1.1: Versatile Grating Machine
16
Fig. 1.2: Hot Air Popping Machine
17
Fig. 1.3: Bio – Plate Forming Machine
18
Fig. 1.4: Integrated Hot Air Roasting Machine
19
Fig. 1.5: Continuous Lemon Cutting Machine
20
Section 2.1.0: Introduction
As traditional staple foods in India, Chapathi and Poories stand
next only to cooked rice. In northern parts of the country Chapathi and
Poories are the main staple foods. In large number of industrial and
military canteens hundreds of Chapathis/Poories are prepared and
consumed daily. All the preparatory operations are carried out manually,
which is tedious and time consuming. Attempts to produce and market
pre-cooked and packed fast foods; especially Chapathi are being made
by some agencies with very little success. One of the problems in their
attempts being the non-availability of suitable machinery and gadgets for
preparing them on a large-scale. In case a device is made available for
making Chapathi, from dough mixing to baking/frying, would result in
reduction in labor and drudgery to cater to large number of people in short
time in serving Chapathi of uniform quality. The mechanization would
pave way for the production and marketing of precooked and packed
Chapathi as convenient food in large volumes hygienically.
The design problem can be best approached through a
combination of theory, modern knowledge of materials, awareness of the
limitations and practicability of various production methods. The finest
workshop facility with the most up-to-date machine tools enabling
economic production will be no good if the designer has not done the
work satisfactorily. Machine members have to be so sized, in order to with
stand the resulting stresses and deformation and at the same time
transmit the required motion with constant or variable forces acting on
21
them. The machine elements are to be sized keeping in view the criterion
of wear and the environmental conditions like temperature, corrosion and
other ambient conditions. Since there are many ways of addressing the
same problem and no rigid rules are applicable, as the designers must
rely upon models and other testing techniques to determine whether the
machine will perform satisfactorily.
The successful operation of any machine depends largely on the
kinematics of machines. The motion of parts is largely of rectilinear and
curvilinear type. Rectilinear type includes unidirectional, reciprocating
motion while curvilinear type includes rotary, oscillatory and simple
harmonic motions. Design is a process of prescribing the sizes, shapes,
material composition and arrangements of parts, so that the resulting
machine will perform the prescribed task.
Roti and Chapathi are the staple food in India and different type of
these unleavened breads are prepared from wheat and are baked on a
steel plate (tava) and puffed by bringing it in contact with live flame for a
brief period. Chapathi, normally hand rolled by a pin and plate are baked
on pan using fat. Fermented dough using yogurt and rolling out to give a
layery fried product is called the Bhatura. An Indian styled well-insulated
oven is used for the preparation of unleavened bread called the Tandoori
Roti. Naan is made of maida, the white inner flour of wheat, which is
leavened before baking to yield a thick elastic product.
The numerical values of thermo physical properties of food
products are necessary for design, optimization, operation and control of
food processing plants and quality evaluation of products. Most of the
22
design and operation of food process and processing equipment have
been based more on the industrial experience and empirical rules, than
on engineering science. This is due to the complex physical and chemical
structure of raw and processed foods and the diversity of food processing
operations and equipment. Advanced mathematical modeling, computer
simulation, process control and expert systems of food processing require
quantitative data of transport and other engineering properties.
Previously, heat transfer analysis for heating or cooling of food
products employed constant uniform values of thermal properties. These
analysis being over simplified were always inaccurate. Present day
analytical techniques such as finite element and finite difference methods
are much more sophisticated and can account for non-uniform thermal
properties, which change with time, temperature and location as a food
product is heated/cooled. This greatly increases the demand for more
accurate thermal property data and more sophistication in the sense it is
necessary to know how thermal properties change during a process.
Though there are many reports on the measured values of the
thermal properties as well as on mathematical models for their estimation,
it is often necessary to make measurement for special cases, or at least
to verify the literature values or the validity of the models because of the
great variation in origin, composition and processing of food.
Literature Survey
There are very few reports of development of machinery for Indian
traditional foods. Some of the machines designed and developed earlier
23
are a) Continuous Chapathi machine based on screw extrusion and three
tier baking oven (Gupta, et al., 1990), b) Design and development of an
Idli machine and vada machine (Nagaraju, et al, 1997), c) Dosa machine,
Boondi machine, Bio-Plate casting machine, Grating machine, Laddu
machine (Venkateshmurthy, et al., 1997, 2000, 2002, 2004) and
Continuous Rice cooker (Ramesh, et al., 2000).
The theoretical aspects of the estimation of thermal properties
such as specific heat and thermal conductivity, in order to design
continuous baking oven for Chapathi, Indian unleavened flat bread has
been described (Gupta, 1990). Though a good amount of work has been
reported on thermal conductivity of biological materials, practically no data
is available for wheat dough and baked Chapathi. The work on the
process for the preparation of quick cooking Rice with increased yield,
reduced processing cost has been reported (Ramesh, 2000).
A review of the status of machinery for Indian traditional foods and
the need for mechanization with emphasis on reduced processing cost
with hygiene for the Indian food machinery manufacturers has been
presented (Ramesh, 2004).
Data on thermal properties of food products are needed to
understand their thermal behavior and to control heat transfer processes.
Knowledge of thermal properties is essential for mathematical modeling
and computer simulation of heat and moisture transport (Rask, 1989;
Sablani et al., 1998). Inspite of many reviews and books, data are not
available for many food products and needs to be generated.
24
Since most foods are hygroscopic in nature, one should consider
how strongly they bind water, for instance, moistures-solid interaction
during drying (Wang and Bernnam, 1992).
The main parameter that
significantly influences the thermal properties of the bulk of food is the
moisture content. This is because the thermal properties of water are
markedly different from those of other components (Proteins, fats,
carbohydrates and air).
Presence of water also causes a strong temperature dependence
of thermal properties. A general review on thermal properties of food has
been brought out by Mohesnin (1980). The thermal properties of variety
of grains (Polley, et al., 1980), potato (Lamberg and Hallstorm, 1986),
dough and bakery products (Rask, 1989) have been reported.
The properties of particulate foods are more difficult to predict, due
to their variable heterogeneous structure and porosity (Wallapapan, et al.,
1986). Therefore, experimental measurements are especially important
for this class of food products.
In situations where heat transfer occurs at an unsteady state,
thermal diffusivity (α) is more relevant. The value of ‘α’ determines how
fast heat propagates through a material; higher values indicate rapid heat
diffusion. The ‘α’ of a material is defined as the ratio of the heat capacity
of the material to conduct heat divided by its heat capacity to store it
(McCabe, et al., 1995; Charm, 1971; Heldman and Singh, 1993; Perry
and Green, 1984).
The objection to steady state analysis is the long time required to
attain the steady state conditions, which in turn lead to changes in
25
compositions during measurement, migration due to temperature
difference across the material for a long period of time. Generally,
measurement of thermal properties require sophisticated and expensive
equipment (Urbicain and Lozano, 1997).
The transient method has been successfully applied to the
measurement of thermal conductivity of various food products such as
pigeon pea (Shepherd and Bhradwaj, 1986).
Polley, et al., (1980) have compiled data on specific heat (Cp) of
vegetables and fruits. Gupta (1990) reported the specific heat (Cp) of
unleavened flat bread (Chapathi) and other foods as well. Lamberg and
Hallstrom, (1986) have reported specific heat (Cp) over the temperature
range of 20 to 90°C and a moisture range of 8 to 85% (wet bulb) of
freeze-dried Brintje potato. The specific heat is often measured using the
method of mixing, adiabatic calorimeter, differential scanning calorimeter
(DSC) and differential thermal analysis (DTA). The DSC techniques have
been vividly discussed by Callanan and Sullivan (1986). The guarded hot
plate method can also be used for measurement of specific heat (Cp).
Design of Traditional Food Machinery
The design problem can be best approached through a
limitations and practicability of various production methods as discussed
earlier. Various steps involved in the design process could be
summarized as a) the aim of the design, b) preparation of the simple
schematic diagram, c) conceiving the shape of the unit/machine to be
26
designed, d) preliminary strength calculation, e) consideration of factors
like selection of material and manufacturing method to produce most
economical design, f) mechanical design and preparation of detailed
manufacturing drawing of individual components and assembly drawing.
The selection of the most suitable materials for a particular part
becomes a tedious job for the designer. This is partly because of the large
number of factors to be considered which have bearing on the problem.
This is also because of the availability of very large number of materials
and alloys possessing most diverse properties from which the materials
has to be chosen. With the development of new material, a good
knowledge of heat treatment of materials which modifies the properties of
material to make them most suitable for a particular application is also
very important.
The material selected must posses the necessary properties for the
proposed application. The various requirements to be satisfied are weight,
surface finish, rigidity, ability to withstand environmental stress, corrosion
from chemicals, service life, reliability etc. The four types of principal
properties of material decisively affect their selection, namely, physical,
mechanical, chemical and ease of machining.
The thermal and physical properties concerned are co-efficient of
thermal expansion, thermal conductivity, specific heat, specific gravity,
electrical conductivity and magnetic property. The various mechanical
properties are strength in tensile, compressive, shear, bending, torsion
and fatigue as well as impact resistances. The properties concerned with
the manufacture are the weldability, castability, forgeability, deep drawing
27
etc. The various chemical properties concerned are resistance to acids,
oxidation, water, oils etc.
For longer service life, the parts are to be dimensioned liberally to
give reduced loading and due consideration given to its resistance to
thermal, environmental and chemical effects and also to wear. Stainless
steel, an iron base alloy is manufactured in electric furnace. It has a great
resistance to corrosion. The property of corrosion resistance is obtained
by adding chromium or chromium and nickel together. Selection of
material for food processing machinery is an added task for the designer.
For most of the food applications stainless steel is the preferred material
as the food material contains large amount of moisture and product is for
human consumption, needing hygiene. In certain cases, where acid foods
are handled, a special variety of stainless steel having very low carbon
content which has oxidation-resistant property is recommended.
Justification
The design of machinery for Indian traditional foods is a new and
specialized area involving extensive research and experimentation. Very
few organizations are involved in design and development of such food
processing machinery. Most of the food processing machinery available
in the country are imported and most of them are for processing of fruits,
vegetables, bakery products, confectionery and oils. A few industries have
adapted these imported food processing machinery for Indian foods.
Imported submerged fryer and the slicers are used for largescale
processing of Potato chips.
28
The machine design for Indian traditional foods is an exclusive
area for food/mechanical engineers and there are ample opportunities for
mechanization of these foods since it will not come under the purview of
multinational companies (MNC’s).
The objective of the present work is to design and develop
machineries for Indian traditional foods incorporating the different
branches of engineering such as thermal, mechanical, chemical, electrical
and electronic and food engineering. The understanding of the physical,
thermal and engineering properties of foods is very important for the
design of any food-processing machine. Integration of the equipment
developed with the technology of food processing is also considered. In
the present work, design and development of traditional food machinery
such as Chapathi machine is taken up.
Section 2.2.0: Materials and Methods
Section 2.2.1: Materials
Whole-Wheat Flour (WWF):
Commercial medium hard wheat procured from the local market
was cleaned and ground in a disc mill to obtain whole-wheat flour. It
contains different fractions such as maida (soft core of wheat), bran, atta
and germ.
29
Atta (A):
Atta was obtained from International School of Milling Technology
Mill (CFTRI, Mysore). It is one of the fraction obtained from the roller flour
mill and do not contain fractions such as maida, germ and bran.
Section 2.2.2: Methods
Measurement of Temperature
A digital temperature indicator (Model–TFF 200, Make–EBRO,
Germany, PT-100, Range: -50 to 300• C) was employed to measure the
temperature of the hot plate as well as the product temperature. The
temperature indicator had a resolution of 0.1• C with a least count of 0.1 •C.
Determination of Thermal Conductivity
Chapathi were baked on the hot plate by discharging a known
amount of dough of predetermined consistency (Venkateshmurthy, et al.
1998). The probe of the temperature indicator was positioned through a
hole at the center of the Chapathi disc to measure the product surface
temperature. Thermal conductivity was calculated from these test results
by using appropriate terms in equation (5) and (6).
Sieve Analysis of the Flour
Sieve analysis of the flour samples were carried out in a Buhler
Laboratory plan-sifter (Type MLU-300), using 200 g samples. The over
30
tailings on each sieve were weighed after 10 min of sieving and
percentages were calculated on a total flour weight basis.
Chemical Analysis
Flour moisture, gluten, ash and damaged starch were estimated by
standard AACC methods (1983).
Rheological Characteristics
Farinograph characteristics of Chapathi dough prepared in a
Hobart mixer were determined by transferring the dough equivalent to 50
g flour (14% moisture basis) to a 50 g mixing bowl of the Farinograph.
The dough was mixed for 10 min at 1:3 lever position and various
parameters like peak consistency, dough development time (DDT),
stability and elasticity were assessed from a farinogram in accordance
with the AACC methods (1983).
Extensograph characteristics of Hobart-mixed Chapathi dough
were measured with 100 g dough instead of generally used 150 g dough.
However, 50 g weight was placed on the dough hook, while stretching the
dough, to compensate for the lower dough weight. The extensograph
characteristics were measured as per the standard methods (AACC,
1983). Compliance and elastic recovery of the dough were measured
using a penetrometer (Sai Manohar and Haridasrao, 1992).
The consistency of the Chapathi dough was measured in RWAM
as per the method described earlier (Haridasrao, et al., 1987).
31
Hand Sheeting
For comparing the quality of machine-made Chapathi, about 35 g
dough was sheeted using a rolling pin and a rectangular frame with
adjustable height 1.5 mm as per the method described earlier
(Haridasrao, et al., 1986). The thickness as obtained in the Chapathi
sheet was maintained to the same thickness as obtained in the Chapathi,
sheeting device.
Baking of Chapathi
Baking of Chapathi was done on a hot plate, followed by puffing on
a gas flame as per the standard procedure (Haridasrao, et al., 1986).
Statistical Analysis
Statistical analysis of the data was carried out according to Duncan
New Multiple Range Test (Snedecor and Cochran 1968).
Section 2.2.3: Design of Machine
Chapathi Machine
The Chapathi machine as shown in Fig. 2.1 comprises of two
major sub-assemblies, namely, 1) Chapathi sheeting unit and 2)
Chapathi-baking unit. Both these units are integrated to produce Chapathi
continuously in largescale automatically. In order to protect the invention,
the machines are covered by three Indian patents.
32
1. Chapathi Sheeting Unit
The Chapathi sheeting unit consists of pneumatic extruder and a
dusting and cutting device as the main sub-assemblies as shown in Fig.
2.2.
Pneumatic Extruder
The pneumatic extruder is an important sub-assembly of the
Chapathi sheeting unit. The device as shown in Fig. 2.3 the extrusion is
based on compressed gas. The device comprises of a conical vessel,
having flanges at its top and bottom, with a provision for admitting
compressed gas. A plate having a slot, fixed gas tight on to the bottom of
the cylindrical vessel with suitable gasket. A pair of plates is bolted to the
bottom plate for varying the thickness of the extruded sheet. The cover
plates of the vessel may have additional means such as bolt and nut to
make it gas tight.
The rested (15 min) dough was transferred to the conical vessel of
Chapathi sheeting unit. The dough was extruded by compressed air under
air pressure (4±1 kg/cm2) through a slit adjusted to a width of 0.8 mm. The
air pressure was adjusted such that the rate of extrusion was maintained
constant at 800 mm per min. The circular-shaped discs are cut from
Chapathi dough.
The conical vessel has the drawback of cavitation, which led to the
escape of the compressed air and non-uniform extrusion.
33
In order to overcome the above drawbacks, an improved
pneumatic
extruder,
as
shown
in
Fig.
2.4
was
developed
(Venkateshmurthy, et al., 2000). The improved device has the ability for
the extrusion of dough into sheet or strands of uniform thickness at a
constant rate.
A Device for Dusting and Cutting of Dough Sheet
The design relates to a device for dusting and cutting of dough into
any geometrical shape as shown in Fig. 2.5. Geometrical shapes
obtained by using the device are of uniform dimension and obtained
continuously. The dough employed are wheat dough, urdh dough. The
invention is therefore useful as a sub-assembly for the Chapathi-sheeting
unit for dusting and cutting of Chapathi.
2. Chapathi Baking Unit:
The cross sectional view of the Chapathi-baking unit is shown in
the Fig. 2.6. The Chapathi discs are baked on a set of hot plates on both
the sides. The oil is applied on both sides through an oiling device. The
machine has the provision for varying/controlling of the baking time/
temperature through an AC drive and temperature controller respectively.
The baked Chapathi are discharged through a discharge chute.
34
Preparation of Chapathi Dough
Dough was prepared from both whole-wheat flour as well as Atta.
It was prepared by mixing 3 kg of flour and water for 3 min in a Hobart (N200) mixer at low speed. Water amounting to 1.95 L and 1.74 L was used
in the case of whole-wheat flour and atta, respectively. The temperature
of the mixed dough was adjusted to 27° C by altering the temperature of
water. The consistency of the dough was measured after 15 min of
relaxation time using Research Water Absorption Meter (RWAM).
The wheat flour used for standardization of the pneumatic extruder
was found to have initial moisture of 11.4% max. From the preliminary
experiments it was found that optimum added moisture to be 67% for the
pneumatic extrusion. Thus the total moisture of the wheat dough/Chapathi
disc is 78 %. The moisture loss during baking is in the range of 19 ~ 29 %
of the initial weight of the Chapathi disc.
Energy Balance
The liquid petroleum gas (LPG) a blend of butane and propane in
the ratio of 60:40 (commercially available gas is used as heat source).
From the theoretical calculation the requirement of the LPG for supplying
the required heat to the hot plate is estimated to be around 640 g,
considering the heating value/calorific value of the LPG as 11,642 Kcal/
kg. It was reported that 30 kg of air is required for complete combustion
of the LPG. The circular burner is provided with a gas mixing tube (for
mixing of air and LPG for complete combustion), which balances the air
fuel ratio of 30:1 and the outlet is provided with holes of 3.5 mm diameter,
35
where the actual flame heats the circular hot plate. A diffuser tube is
provided inside the burner to lower the pressure of the LPG (which is at
higher pressure inside the filled cylinder) and also its uniform distribution.
From the preliminary experiments, it was found that the baking time
of the Chapathi depends on the thickness of the disc and the moisture
content of the dough disc and found to be ≈60 s for each side. The
rotational speed of the Chapathi-baking unit is designed for a total baking
time of 120 s and the speed variator has the provision even for the
incremental variations.
From the large-scale trial runs, it was noticed that the actual
consumption of the LPG was found to be around 1.25 Kg, which is more
than the theoretical estimates. The variation in consumption of the gas
can be attributed to the heat loss occurring in different parts of the baking
unit and the major heat loss in the baking unit is from the hood. Thermal
efficiency of the Chapathi baking unit is estimated to be around 51%.
Section 2.3.0: Results and Discussion
Section 2.3.1: Design and Development
1. Chapathi Sheeting Unit
The Chapathi sheeting unit, as shown in Fig. 2.2 comprises of a
pneumatic extruder, dusting sub-assembly, circular moving cutters,
cutting roller, return conveyor, diverters/chutes and main drive. The
concept of extrusion of food material using compressed air has been tried
out for the first time. The device is useful for the extrusion of any dough,
36
particularly farinaceous dough, into sheet or strands. The sheet or strands
extruded using the device are uniform in thickness and extruded
continuously. The dough employed are wheat dough, urd dough and
invention is useful as an accessory to Chapathi machine. The pneumatic
extruder is housed on to the main frame of the Chapathi sheeting unit. In
order to reduce the stickiness of the extruded sheet, two dusting subassemblies are provided for dusting of the dough sheet on both the sides.
The extruded sheet is allowed to fall on to the moving circular
cutters/plates, where in the cutting rollers cuts the rectangular sheet into
circular discs. The circular discs are transferred to the baking unit and the
uncut extra sheet is reused for further sheeting.
Pneumatic Extruder
As discussed earlier, the pneumatic extruder is an important subassembly of the Chapathi-sheeting unit. The device as shown in Fig. 2.3
the extrusion is based on compressed gas. The device comprises of a
conical vessel, having flanges at its top and bottom, with a provision for
housing suitable gaskets a cover plate having a quick fix coupling on its
top at its center for admitting compressed gas into the vessel. The bottom
of the cover plate being provided with a gas deflector for preventing the
gas directly impinging on the dough mass contained in the vessel. The
cover plate rests over the flange at the top of the vessel and in between
the cover plate and the flange, a suitable gasket being provided to make
the arrangement gas tight. A plate having a slot, fixed gas tight on to the
bottom of the cylindrical vessel with suitable gasket. A pair of plates is
37
bolted to the bottom plate for varying the thickness of the extruded sheet.
The cover plates of the vessel may have additional means such as bolt
and nut to make it gas tight. The conical or trapezoidal shape of vessel is
preferable in the case of dough for making Chapathi because the hold-up
volume of the dough is less, when compared to a cylindrical one and
leakage of the compressed gas is reduced as the dough forms a wedge in
the conical or trapezoidal vessels.
However the pneumatic extruder discussed above was found to have
the following drawbacks.
•
Due to the conical shape of the vessel the rate of extrusion will
vary, as extrusion proceeds.
•
The force applied during extrusion also varies as the crosssectional area continuously changes, as extrusion proceeds.
•
Due to non-uniform flow of the dough inside the vessel during
extrusion, cavitation of the dough occurs.
•
The frictional resistance offered for the flow of the dough is more.
•
The cavitation of the dough during extrusion abruptly ends the
process of extrusion due to release of the compressed air.
•
Large amount of dough is leftover in the vessel.
•
The dough sheet had poor surface finish.
•
Variations in the rate of extrusion of the dough leading to nonuniform sheet of dough.
38
An improved pneumatic extruder was developed in order to
overcome the above drawbacks (Venkateshmurthy, et al., 2000). The
main object of the improved device for extrusion of dough into sheet or
strands based on the principle of pneumatic extrusion in a cylindrical
vessel, which obviates the above noted drawbacks. The improved device
has the ability for the extrusion of dough into sheet or strands of uniform
thickness, at a constant rate. The invention is also to provide a device
wherein the force applied during extrusion remains constant. Further there
is uniform flow of the dough inside the vessel during extrusion wherein the
cavitation of the dough during extrusion is avoided, which enables a
continuous operation of sheeting thereby making leftover dough in the
vessel negligible.
The improvements incorporated into the pneumatic extruder as
shown in Fig. 2.4, overcomes most of the drawbacks of the earlier design
employed for the production of sheet.
This improved device consists of a cylindrical vessel, having
flanges at its top and bottom and the cover plates have projections for
housing suitable gaskets. The top cover plate has a quick fix coupling on
its top for allowing the compressed gas into the vessel. The cylindrical
vessel is provided with a sliding piston with suitable handle and an air
vent. The piston is provided with a rubber ‘O’ ring to make the device leak
proof. In between the cover plate and the flange, a suitable gasket being
provided which rests on the flange to make the arrangement gas tight. A
39
plate having a slot is fixed to the bottom of the cylindrical vessel with a
suitable gasket. A pair of strips is bolted to the bottom plate. The cover
plates and top portion of the vessel may have additional means such as
bolt and nut to make the cylindrical vessel gas tight.
The material of construction should withstand the pressure at
which the improved device is operated. Particularly in the case of sheeting
of Chapathi the pressure used is 2.5 to 6 bars. The bottom cover plate
has a blind slot at its center. This slot may be preferably of 200 mm length
and 8 mm width. Tapped holes are provided on the bottom cover plate, to
attach suitable strips for varying the size and shape of the extruded sheet.
The strips may also be of the same material as that of the cylindrical
vessel and preferably stainless steel. Such an arrangement will be useful
to control the thickness of the extruded sheet. This improved device can
be attached to a cutting unit, which can produce Chapathi,, of different
shapes such as circle, triangle, square, rectangle etc. This should not be
construed to restrict the use of the device for making Chapathi only. It is
to be noted that the device can be used for making other similar food
articles such as Papads, Noodles etc.
The working of the device is explained below with particular
reference to sheeting of Chapathi.
Dough out of whole wheat flour or atta with an initial moisture
content of around 8-12 % is prepared by adding water of about 50 ~ 68 %
and 5 % of fat (groundnut oil) and 3 % common salt. Ingredients are
mixed in a planetary mixer for about 3 min. The dough is covered with a
polyethylene sheet to prevent evaporation and allowed to relax for about
40
15 - 20 min. Then the dough is charged into the extruder vessel and admit
compressed air or nitrogen or carbon dioxide gas into the vessel at a
pressure of around 2.5 - 6 bar (g). Sheet will be extruded at a rate of
about 800 mm/min. Sheet width would be 175 mm as the slit on the
bottom plate is adjusted to 180 mm and thickness around 0.8-1.2 mm.
This extruded dough sheet is allowed to fall on the slat cutter of a
Chapathi-sheeting unit as described earlier. The linear velocities of dough
sheet and slat cutter are synchronized. The bottom and topside of the
dough sheet is dusted with dry flour to avoid sticking of dough sheet to
slat cutter and cutting roller. When the dough sheet is spread on the slat
cutter and the slat cutter passes beneath the Teflon roller, the circular
discs are formed in the dimple of the slat cutter. The uncut dough sheet is
transferred on to a return conveyor and collected in a tray. It is possible to
vary extrusion rates easily by controlling the air pressure. Air pressure can
also take care of the variations in the rheological characteristics of the
dough.
The main advantages of this invention are:
•
The dough inside the cylindrical extruder is isolated from the
compressed air by a piston.
•
The frictional resistance for the smooth flow of the dough is
minimum.
•
There is no cavitation during extrusion and this is due to the
presence of piston.
41
A Device for Dusting and Cutting of Dough Sheet
The device for dusting and cutting of dough into any uniform
geometrical shape as shown in Fig. 2.5.
This device comprises of a geared motor fixed to a frame, slat
cutter assembly, having been bolted on a chain conveyor. The edge of the
slat cutter having been tapered to an angle of 15~40° and the chain
conveyor being driven by a pair of sprockets. The shaft in turn housed in
antifriction bearings. The sprocket assembly being driven by the geared
motor through a roller chain. The roller assembly consisting of roller and
bearing plates being fixed to the top of the frame. The roller being housed
inside the plate, which imparts the roller, a 6 degree freedom. The roller
being placed such that it rests on the slat cutter and the dough sheet is
formed into geometrical shapes because of the self-weight of the roller.
Two dusting assembly being located, one before the roller for spraying
flour dust on the conveyor and the other after the roller for spraying on top
of the dough sheet. The dusting assemblies consisting of a tube closed at
both ends fitted with a sieve at the bottom and a hopper on its periphery.
A rotary brush is operating within the closed tube, capable of spraying dry
flour when the rotary brush passes against the perforated sieve. A return
conveyor is provided for transferring the uncut portion of the dough sheet
for reuse. The cut circular Chapathi discs are collected in a tray through
the perforated chutes. All the above said assemblies are mounted on an
angle frame, which is covered on all its sides. The whole assembly is
mounted on swivel castors for easy movement of the unit to the required
42
place. The Chapathi discs are collected and fed on to the Chapathi baking
oven.
Chapathi-Baking Unit
The Chapathi baking unit, as shown in Fig. 2.6 is based on the
concept of rotating hot plates. The Chapathi disc formed by using the
pneumatic sheeting unit is transferred to the first rotating hot plate through
a chute/guide. The disc after baking on one side on the first hot plate to
the predetermined time of 50 s and is transferred to the second hot plate.
During the transfer of the Chapathi disc from the first hot plate to the
second hot plate, it turns over to the other side during its free fall. The
Chapathi disc is allowed to bake on the second hot plate to the pre-set
time of approximately 50 s. Oil is dispensed on both sides of the Chapathi
disc through an oil dispenser for better heat transfer. The baked
Chapathis are transferred to the outlet chute, by a diverter placed on the
second hot plate, and collected in a tray. The circular rotating hot plates
are driven by an electric motor and a gearbox, having a very high velocity
ratio of 1: 3600. A set of pulleys and belt is used for connecting the motor
to the gearbox. The power transmission from the gearbox to the hot plates
is through a set of vertical shaft having key way and a key. The hot plates
are rotated at a pre-determined speed (to vary the baking time of the
Chapathi) by a speed variator. The electric motors are rated for an AC
supply frequency of 50 Hz and rotate at 1440 RPM. The supply frequency
can be varied in order to vary the speed of the electric motor and an AC/
frequency drive is used for varying the drive frequency of the electric
43
motor. The recommended lowest frequency, which the electric motor can
be run, is as low as 10% (5 Hz) of the rated frequency. The bearing
supports are mounted on to the main frame of the Chapathi-baking unit.
The selection of the hot plate material is limited to an alloy steel of C-40
(BIS) quality due to cost consideration and ease of machineablity and the
reported thermal conductivity of the C-40 alloy steel is 51.80 W/m°C. A
circular gas burner is provided at the bottom of the hot plates, concentric
to them. The baking temperature of the Chapathi can be controlled by
varying the temperature of the hot plate through a temperature controller
having a measurable range of 400° C and provided with a PT-100
thermocouple. The temperature controller connected to the solenoid valve
controls the supply of the liquid petroleum gas (LPG) into the circular
burner. The thermocouple is placed on the hot plate and is in contact
during the rotation of the hot plate. A solenoid valve is coupled to the
circular burner either to stop/allow the liquid petroleum gas as required
and will act as safety against electrical power failure. The temperature
controller sends the signal to the solenoid to regulate the pre-set
temperature of the hot plate. All the parts in contact with the food
materials are made of stainless Steel of AISI – 316 quality.
Section 2.3.2: Standardization of Chapathi Dough
There is considerable quality difference between Atta (A) and
Whole-wheat flour (WWF) with respect to moisture, ash, damaged starch
and water absorption capacity (Table 2.1). The lower moisture and higher
values for ash, damaged starch and water absorption capacity of whole-
44
wheat flour as compared to atta, confirm the earlier reported values
(Haridasrao et al., 1983). The whole-wheat flour was finer than atta, as
indicated by the over-tailings on129 µm sieve, which was 30.4%, when
compared to 52.8% observed for atta.
Water required to prepare
Chapathi dough of desired consistency was 68% for whole-wheat flour
and 61% for atta. The higher water absorption of whole-wheat flour was
attributed to its higher damaged starch content of 15.1% as compared to
7.3% for atta.
Rheological characteristics of Chapathi dough:
The resistant of extension decreased, while the extensibility
increased with the increase in the amount of water (Table 2.2).
The
change in the above characteristics were higher for atta as compared to
whole-wheat flour. The dough made from whole-wheat flour was softer as
compared to those made from atta, as indicated by the compliance
values. The elastic recovery, which indicated the gluten development, was
not influenced by the amount of water used in the present study.
However, the values were higher for dough made from atta. This could
be attributed to the presence of more gluten-containing endosperm and
lower bran content.
Dough development time and stability of doughs
were effected slightly with water.
Salt increased the toughness of the dough based on the wholewheat flour, as indicated by the increase in the resistance to extension
from 400 to 520 BU, while fat reduced the same from 400 to 360 BU.
Incorporation of salt and/or fat increased the extensibility of the dough.
45
Addition of salt decreased the compliance of doughs from 41.1 to 40.0 %,
but the same considerably increased to 46.5% with addition of fat.
Maximum softness of dough was observed, when both salt and fat were
added together, as indicated by a higher compliance value of 47.1%
(Table 2.2).
However, resistance to extension value was in between,
when fat or salt was added alone to the dough. The elastic recovery was
slightly affected with fat, as it decreased only by 2.1%, while with salt, it
increased by 23.4%. In case of atta, though the trends remained the
same, the effect with salt and/or fat on compliance and elastic recovery
was considerable and greater than those observed for whole-wheat flour
dough due to lower bran content.
The peak consistency of dough, as indicated in farinograph, was
reduced considerably with salt and fat. Similar observation was made
earlier for wheat flour dough (Tanaka et al., 1967). Slight increase in the
stability were observed on addition of salt for both whole-wheat flour and
atta dough. The mixing tolerance index, which was inversely related to
the stability, decreased considerably with salt and the decrease was more
for dough made of atta, compared to that made of whole-wheat flour.
Based on the largescale trials of the Chapathi sheeting unit, the slit width
of the pneumatic extruder was optimized. Contraction of sheet was
observed due to elastic nature, resulting in the increase of thickness
(Table 2.3). The slit width of 1.2 mm yielded Chapathi sheet of 2.05 mm
thickness; thereby indicating a 2/3rd increase in the thickness. However,
at lower slit width of 0.6 mm the thickness of the sheet was found to be
nearly double the slit width. It was observed that 0.8 mm slit width was
46
optimum to get a Chapathi sheet thickness of 1.5 mm. The increase in
the thickness was greater in case of atta dough, possibly due to lower
amount of bran present, thus making the dough more elastic.
Sheeting Characteristics
The sheeting characteristics of Chapathi dough prepared from atta
and whole-wheat flour with varying levels of water are presented in Table
2.4. Dough prepared with water equivalent to Chapathi water absorption,
having an extrusion time of 60±5 s determined by RWAM had a tendency
to stick to the cutter and resulted in a non-uniform Chapathi sheet.
Hence, for obtaining a continuous sheet with good machineablity, water
had to be reduced. Different trials indicated that the consistency of the
dough should be around 110 s for atta and 120 s for whole-wheat flour.
The pressure required to extrude the dough naturally decreased from 4.5
to 3.5 kg/cm2 with an increase in water from 56 to 60%. The decrease in
weight with more water could possibly be due to higher extensibility and
lower resistance to extension of the dough (Table 2.2). This was also
reflected in the decreased thickness of the Chapathi sheet with the
increment of water. The scrap dough quantity, irrespective of the amount
of water used, remained almost same and it ranged from 38 to 42%.
In case of whole-wheat flour, it was observed that the weight of
Chapathi disc was lower, though the same slit width was kept and it
increased from 25.8 to 29.2 g with an increase in water from 63 to 67%.
Lower weight of Chapathi disc in case of whole-wheat flour could be
attributed to the lower thickness of Chapathi sheet possibly due to lower
47
elasticity of dough, containing higher amount of bran.
The pressure
required to extrude the dough was less, even though the extrusion time
determined was higher as compared to atta. The higher extrusion time
could be possibly due to the stickiness of the whole-wheat flour dough.
The pressure required to extrude the dough increased considerably
from 3.0 to 5.0 kg/cm2 (Table 2.4), due to stiff nature of the dough on
addition of salt. This was also confirmed by decrease in the compliance
value.
Addition of fat, however, softened the dough, as shown by
decrease in the extrusion time from 120 to 65 s. Hence, the pressure
required to extrude the dough also decreased on addition of fat.
Incorporation of fat and salt together required 4.0 kg/cm2 pressure to
extrude the dough, which is in between the pressure required to extrude,
when salt (5.0 kg/cm2) or fat (3.5 kg/cm2) were added alone.
The
Chapathi disc made from dough, containing fat had lower weight (27.0 g),
possibly due to its extensible nature as compared to that observed for
control dough (27.7 g). This was also reflected by its lower thickness,
being 1.30 mm with fat and 1.5 mm with salt and 1.47 mm in control
dough. The Chapathi disc containing salt required low amount of dusting,
as it was less sticky.
2. Baking Characteristics
The quality of Chapathis prepared at different water levels (Table
2.5) indicated that the puffed height increased from 6.5 to 7.0 cm with an
increase in water from 65 to 67% in case of whole-wheat flour. Similar
trend was also observed in case of Chapathi made with atta, but the
48
puffed height was higher in Chapathi prepared from atta, possibly
because of lower bran content, making it more extensible. The Chapathi
containing higher level of water than optimum, required extra baking time
of 30 to 45 s. These Chapathi had softer texture and were more pliable
due to greater gelatinization.
The puffed height of Chapathi prepared from atta or whole-wheat
flour, reduced with addition of salt or salt and fat, because of the stiff
nature of dough. Incorporation of fat alone lowered the puffed height from
8.0 to 5.7 cm, due to its poor water vapour retention capacity, but the
Chapathi was more pliable. The Chapathi made with salt was slightly
chewy and tough, when compared to control Chapathi made without it, as
the salt changed the protein quality.
The quality of Chapathi made manually and mechanically showed
negligible difference in them (Table 2.6). The puffed height of Chapathi in
both the cases was similar (8.05 cm) and no difference was observed in
other sensory quality characteristics. This indicated that the quality of
Chapathi was not adversely affected, as a result of mechanical sheeting.
In the case of a conventional hot plate used domestically for
Chapathi baking, conduction from hot plate which is heated at the bottom
by heat source such as firewood, charcoal, coal, kerosene, liquefied
petroleum gas (LPG) is most important. Chapathi is heated for about 45 ~
60 s on each side and the mode of heat transfer is by conduction alone.
Dough was prepared by mixing 3 kg of flour and water for 3 min in
a Hobart (N-200) mixer at low speed. Water amounting to 1.95 and 1.74
L was used in the case of whole-wheat flour and atta, respectively. The
49
temperature of the mixed dough was adjusted to 27° C by altering the
temperature of water. The consistency of the dough was measured after
15 min of relaxation time using Research Water Absorption Meter
(RWAM). The wheat dough is transferred to the sheeting unit and the
sheeting is done by admitting compressed air into the pneumatic extruder.
The extruded sheets are allowed to fall on to the hot plate, which is
preheated (220~245ο C) and oil is sprayed on top of the Chapathi to
enhance heat transfer, flavor and texture. Chapathi is very popular in
south India and the above recipe refers to one of the many different
varieties of Chapathis prepared.
It is widely acknowledged that the mode of heat transfer is more
important than just supplying the required quantity of heat for obtaining
the desired product characteristics such as flavor, crustiness and color.
Hence, it was thought desirable to analyze the effect of modes of heat
transfer, in baking of Chapathi on these characteristics as well. A
mathematical expression was developed to analyze the mode of heat
transfer, which is expected to be useful in improving the Chapathi
characteristics as well as in modifying the design of the Chapathi-baking
unit.
Section 2.3.3: Heat Transfer Analysis
1. Thermal Properties
To design a continuous baking oven for Chapathi, it is necessary to
know the thermal properties of whole-wheat dough and Chapathi. For
determination of thermal conductivity either transient or steady state heat
50
transfer methods are used depending upon the nature of materials.
Although a good amount of work has been reported on thermal
conductivity of biological materials, no data are available for thermal
conductivity of wheat dough and baked Chapathi.
The transient line heat source method has been used for
determination of thermal conductivity of peanut pods, hulls and kernels
(Sater et al., 1975) and is suitable for granular materials, although it does
require a fairly sophisticated data acquisition system (Rao and Rizvi,
1986). Another transient method is the Fitch method (Mohsenin, 1980),
which is mostly used to determine thermal conductivity of poor conductors
of heat. Although transient methods are less complicated and require
less time, these cannot be used for materials whose shape and size has
to be maintained.
The guarded hot plate steady state method was used with slight
modification to suit the shape and size of the rolled or baked Chapathi; it
can be used for similar types of other homogenous food materials as well.
Although the present study was limited to a maximum of 63°C, the
apparatus can be used to determine thermal conductivity at higher
temperatures also. (Gupta.1990),
The thermal conductivity values of dough and Chapathi increased
with increase in temperature below 60°C, but above 60°C the value
decreased. This has been attributed to physicochemical changes taking
place above 60°C. Due to these changes, swelling and softening of dough
and Chapathi occur (Gupta. 1990).
51
To design a continuous baking and puffing oven for Chapathi
(Gupta. 1990), it is necessary to know the energy requirement in the
system. Specific heat is one of the thermal properties required to calculate
the energy requirement. Different types of calorimeters have been used
in the past depending upon the structure of the materials, and the method
of mixtures has been most commonly used. Although a large amount of
work has been reported for the determination of specific heat of food
materials, no data are available for specific heat of whole-wheat flour
dough, or cooked and puffed Chapathi.
In situations where heat transfer occurs at an unsteady state,
thermal diffusivity (αc) is more relevant. The value of ‘αc’ determines how
fast heat propagates through a material; higher values indicate rapid heat
diffusion. The ‘αc’ of a material is considered to be the ratio of the heat
capacity of the material to conduct heat divided by its heat capacity to
store it. Many studies on thermal diffusivity of granular foods have been
reported in the literature. There is relative paucity of directly measured α
for food products, while values derived from the constituents are more
common (Jones et al., 1992). Thermal diffusivities of regular shaped
mashed potato (Ansari et al., 1987) by transient method and packed beds
of vegetables pieces (Singh and Chen, 1980) have been estimated.
Many predictive models have also been reported in the literature
(Rahman, 1995) for the determination of α. Most of these models are
specific to the product studied.
An expression which encompasses a
wider range of food products has been developed by Riedel, (1969) and
Martens, (1980).
While the former measured the αc of about fifteen
52
different food products with moisture ranging from 30 to 100 %, the latter
performed multiple regression analysis on 246 published values on α of a
variety of food products and obtained a regression equation.
2. Theoretical Aspects
The mathematical expression for each individual mode of heat
transfer can be written as
Conduction
qCc = k c . Ac. (Tcb − Tct
)
xc
(1)
where qcc is heat transferred by conduction to Chapathi, kJ; kc the thermal
conductivity of the Chapathi, W/m •C; Ac the surface area of the Chapathi
bottom in contact with the hot plate, m2; Tcb Chapathi bottom surface
temperature which is in equilibrium with the hot plate temperature and
equal to it •C.; Tct the temperature of the Chapathi top surface, •C and xc
the thickness of the Chapathi, m.
Convection
q Fc = hFc . Ac . (TRc − Tct )
(2)
where qFc is the heat transferred by convection to Chapathi, kJ; hFc
convective heat transfer coefficient of Chapathi, W/m2 o K; Ac surface area
of the Chapathi bottom in contact with the hot plate, m2; TRc the
temperature of the hot air inside the hood, in oC: Tct the temperature of the
Chapathi top surface, •C.
53
Radiation
(
q Rc = F prc . Ac .σ . T 4 Hc − T 4 ct
)
(3)
where qRc is the heat transferred by radiation to the Chapathi, kJ; Ac
surface area of the Chapathi bottom in contact with the hot plate, m2; σ
the Stefan-Boltzman constant, W/m2 h k4; THc the hood (refractory
surface) temperature, oC: Tct the temperature of the Chapathi top surface,
•
C and Fprc, overall coefficient for radiation heat transfer for Chapathi
baking oven, is given by
F prc = 1
{1
f prc + (1
ε pc −1 )+ ( Ac
Arc ). (1
ε Hc −1)} (4)
where fprc is geometrical factor for Chapathi baking oven; εpc the
emissivity of the Chapathi; Ac surface area of the Chapathi, m2; εHc
emissivity of the Chapathi baking oven hood and Arc area of the radiating
refractory surface of Chapathi baking oven, m2.
Derivations and detailed discussions of these expressions are
given elsewhere (McCabe, Smith & Harmot, 1995; Charm, 1971;
Heldman and Singh, 1993; Perry and Green, 1984).
Total heat transferred to Chapathi can be written as
QTc = qCc + q Fc + q Rc
(4a)
Considering the baking of Chapathi on a rotating hot plate, the
main mechanisms of heat transfer to the Chapathi is conduction from the
rotating hot plate. Convection and radiation heat transfer is not
considered, as the air/flue gas flow is too little. The equation for total heat
transferred to the Chapathi (QTc) can be written using expressions (1), (3)
and (4):
54
QTc = qCc
= k c . Ac . (Tcb − Tct )
(5)
xc
The total heat transferred must be equal to the total heat absorbed
by the Chapathi. Considering the gross temperature rise of the Chapathi
(sensible heat increase) and the latent heat of vaporization of evaporated
moisture, the total theoretical heat absorbed (QAc) by Chapathi can be
expressed as
[
]
Q Ac = Wc . C pc . (Tct − Tcd )
Δtc + [L. λv ]
Δtc
(6)
where Wc is average mass of Chapathi dough, kg; Cpc heat capacity of
wheat flour, kJ/kg o K; Tct the temperature of the Chapathi top surface, •C:
Tcd the wheat flour/dough temperature, oC; Δtc the Chapathi baking time,
h; L the moisture loss during baking, kg; and λv latent heat of water
evaporation, kJ/kg.
The other factors such as heat of reaction, solution and heats of
vaporization of volatiles other than water are usually small and can be
ignored.
In order to test the effect of conductive heat transfer, Chapathi
discs were baked/heated from the bottom on the hot plate of the Chapathi
baking oven at three different preset temperatures. It was observed that
the Chapathi was baked and the characteristic flavor of the Chapathi was
present. This clearly demonstrates the important role of conduction heat
transfer from the hot plate. Thermal conductivity of Chapathi was
calculated by setting the total heat absorbed by the Chapathi equal to the
55
expression for conduction heat transfer in equation (1). The results of
these experiments are given in Table 2.7 and 2.8. Thus, the average
value of thermal conductivity of Chapathi was found to be in the range of
0.29 ~ 0.35 W/m. 0C.
When Chapathi was baked through conduction heat as described
earlier, there was appreciable brown spots on the product surface. This
could be attributed to the fact of the Chapathi being in complete contact
with the surface of the hot plate, indicating the importance of conduction
heating in baking of Chapathi. Using equation (6), the total theoretical
heat absorbed by the test Chapathi was calculated using temperature and
moisture data given in Table 2.9. The value of specific heat (Cpc) is taken
as 1.83 kJ / Kg.
•
K (Gupta, 1990) for computing the sensible heat
requirement of the Chapathi.
The complete heat transfer model as expressed by equation (5)
and (6) was then applied to the baking of Chapathi in the Chapathi-baking
unit. The total heat absorbed by Chapathi [equation (6)] was taken as a
sum of latent heat and sensible heat. On conducting several experiments
each term of equation (5) was calculated for this purpose. The results are
shown in Table 2.9. It can be noted that the out of total heat of 236.25 W,
approximately 151.03 W of the heat absorbed by the Chapathi was latent
heat of evaporation (Q3c) of water while sensible heat (Q2c) was about
85.22 W. The heat transfer indicates the significant contribution from
conduction, which was crucial, for the characteristic flavor and crustiness
of the Chapathi.
56
Thermal efficiency of the Chapathi baking unit was estimated as
described in Table 2.10 using the typical values of the experiments and
found to be about 51.12%.
Section 2.4.0: Conclusions
The design of the Chapathi sheeting machine is optimized based
on the standardization of the process parameters such as moisture
content of dough, salt content and machine parameters such as slit width
of the pneumatic extruder and pneumatic pressure of the extruder.
Similarly the design of the Chapathi-baking unit also is optimized based
on the estimated thermal properties and subsequent heat transfer
analysis, so that desired product quality in terms of characteristic flavor
and crustiness is achieved.
In baking of Chapathi on the Chapathi-baking unit, conduction heat
transfer was found to play the most prominent role. Hence, the amount of
heat supplied by conduction mode of heat transfer has to be controlled
rather than the total heat supplied to the product. The mathematical
expression could be of significant use in estimating the magnitude of the
heat transfer and its contribution, which in turn is useful for design
modifications of the burner and the rotating hot plate of the Chapathi
baking unit. Thermal efficiency of the Chapathi baking unit was estimated
to be about 51.12%.
Then both the units are integrated to result into a Chapathimachine. The design of the machine involved iterative process of
incorporation of minor changes in the machine as well as the dough
57
material. On a few occasions the machine was modified to suit the
Chapathi dough and vice versa. The iterative process continued with
respect to sheeting as well as baking, till the repetitive results at large
scale preparations of Chapathi are obtained. The quality of the Chapathi
made using this machine was comparable to hand made Chapathi.
The photograph of the Chapathi machine is presented as
photograph -1A and 1B.
58
Table 2.1: Chemical and Rheological Characteristics of Flour Samples.
Quality characteristics
Whole wheat
Atta
flour
Chemical
Moisture, %
8.40
11.30
Ash, %
1.24
0.64
Dry gluten, %
10.80
10.40
Damaged starch
15.10
7.32
Water absorption, %
68.0
62.0
Dough development time, min
4.5
3.5
Stability, min
3.5
5.5
Mixing tolerance index, BU
80.0
70.0
Over-tailings on 129 µm sieve, %
30.4
52.8
Farinograph
59
Table 2.2: Effect of Water and Optional Ingredients* on the Rheological Characteristics of Chapathi Dough.
Rheological
Characteristics
Whole Wheat Flour
Water, %
Research Water
Absorption meter
(RAWM)
Extrusion time, sec
Farinograph
Peak consistency, BU
Dough development time,
min
Stability, min
Mixing tolerance index,
BU
Extensograph
Resistance to extension,
BU
Extensibility, * 10-3 m
Area, cm2
Penetrometer
Compliance, %
Elastic recovery X 10,mm
Salt
Atta
Fat
Salt +
Fat
63
65
67
200
120
75
105
65
72
850
1.0
730
0.5
710
0.5
675
1.5
700
0.5
1.0
240
0.5
170
1.0
200
2.5
135
480
400
360
60
36
60
29
37.5
6.95
41.1
7.05
Water, %
56
Salt
Fat
Salt + Fat
58
60
150
110
70
90
45
45
640
1.5
760
1.0
700
1.0
650
1.0
640
1.5
665
1.0
610
1.5
1.0
160
2.0
110
2.0
210
1.5
190
1.5
200
5.0
70
1.0
180
3.5
110
520
360
440
510
470
400
580
360
370
62
28
72
52
76
33
84
45
82
53
87
53
88
45
95
76
100
45
106
57
46.9
7.10
40.0
8.70
46.5
6.90
47.1
8.51
35.6
9.45
40.1
9.48
44.0
9.72
37.7
11.83
49.4
8.27
50.6
10.15
* Salt and fat used at levels of 1.5% and 4% respectively at 65% water for Whole Wheat Flour and 58% water for Atta
60
Table 2.3: Effect of Slit Width on the Thickness of Chapathi Sheet.
Slit width, * 10-3
Chapathi sheet thickness
m
* 10-3
df 76
Whole wheat flour
Atta
m
m
0.6
1.24a
1.30A
0.8
1.47b
1.59B
1.0
1.68c
1.81C
1.2
1.82d
2.05D
0.0134
0.0149
SEM ±
Means of the same column followed by different letters differ significantly (P<0.05) according to Duncan
New Multiple Range Test. df- Degree of freedom, SEM Standard Error Mean.
61
Table 2.4: Effect of Water and Optional Ingredients* on the Sheeting Characteristics of Chapathi Dough.
Characteristics
Whole Wheat Flour (WWF)
Water, %
Salt
Fat
Atta (A)
Salt
Water, %
Salt
Fat
Salt +
+ Fat
Extrusion pressure,
kg/cm
63
65
67
3.5
3.0
2.5
5.0
2.5
1.34
1.4
1.5
1.55c
a
7
8c
Fat
56
58
60
4.0
4.5
4.0
3.5
4.5
3.0
3.5
1.3
1.40
1.6
1.59
1.50
1.66
1.43
1.53
0
d
6A
B
C
A
D
C
df
114
34.
33.6
32.0
36.9
28.3
33.0
B
C
D
E
B
2
Chapathi sheet
thickness, * 10-3 m
b
Chapathi
sheet
weight, g
df
114
25.8
27.
a
b
7
a
SEM
29.
29.9c
c
2
±0.01438
27.
27.8
0
b
A
8
SEM
±0.01438
b
Un-used dough, %
df
114
40
38
SEM
40
41
±0.21
38
42
df
114
38
41
SEM
42
40
±0.26
41
43
* Salt and fat used at levels of 1.5% and 4%, respectively at 65% water for Whole Wheat Flour and 58% water for Atta.
Means of the same row followed by different letters differ significantly (P<0.05) according to Duncan New Multiple Range
Test. df- Degree of freedom, SEM Standard Error Mean.
62
Table 2.5: Effect of Water and Optional Ingredients* on the Quality of Chapathi.
Rheological
Whole Wheat Flour
Atta
characteristics
Water, %
Salt
Fat
Salt + Fat
Water, %
Salt
Fat
Salt
+ Fat
Puffed height, mm
63
65
67
60
65
70
df
61
52
SEM
±0.06
49
56
58
60
70
80
86
df
30
Pliability, mm
21
75
SEM
57
52
±0.05
30
24
26
df
20
29
SEM
±0.03
23
24
25
27
df
30
22
31
SEM
±0.04
28
30
Baking loss, %
26.8
28.9
Appearance
DBN LBU
32.3
19.0
DGNU
LBU
25.9
23.7
DBNU
20.9
19.3
20.2
20.9
23.3
23.6
LBU
LBU
DONU
LBU
DBNU
LBU
U
* Salt and fat used at levels of 1.5% and 4%, respectively at 65% water for Whole Wheat Flour and 58% water for Atta
DGNU – Dull grey non-uniform; LBU – Light brown uniform; DBNU – Dark brown non-uniform;
63
Table 2.6: Comparative Quality Characteristics of Chapathi made by Manual and Mechanical Sheeting.
Quality characteristics
Whole wheat
Atta
flour
Manual
Mechanical
Manual
Mechanical
Puffed height *, cm
6.50
6.43
8.05
8.10
Pliability*, cm
2.40
2.34
2.60
2.55
Baking loss, %
28.96
28.98
19.25
19.20
Appearance
LBU
LBU
LBU
LBU
S
S
S
S
Texture
* NS: Not significant at 5 % level (P<0.05)
LBU – Light brown uniform; S – Soft; SH – Slightly hard
64
Table 2.7: Average Thermal Conductivity (kc) as a Function of Hot Plate Temperature of Whole Wheat Flour.
Thermal
Dough
Mass
Temp. of
Heat
Chapathi
Capacity
Trial
Hot
Chapathi
Chapathi
Total Heat
Conductivity
Mass
of Chapathi
No.
plate
Dia.
Thick.
W
of
kg
kg
Temp.
m
m
Chapathi
(Initial)
(Final)
C
* 10-3
* 10-3
W/m. oC
(Tp)
(Dc)
(xc)
(kc)
(W1)
(Wc)
(Tc)
(Cpc)
o
(QTc)
Sensible
Latent
Heat
heat
(Q2c)
(Q3c)
o
C
(Wheat Flour)
kJ/kg oK
1
220
146
1.34
80.01
141.41
0.2846
0.0258
0.0183
120
1.83
2
225
150
1.47
84.52
151.69
0.2715
0.0277
0.0197
110
1.83
3
230
151
1.58
91.13
160.00
0.3167
0.0292
0.0207
124
1.83
65
Table 2.8: Average Thermal Conductivity (kc) as a Function of Hot Plate Temperature of Atta.
Dough
Mass
Trial
Hot
Chapathi
Chapathi
Total Heat
Thermal
Mass
of Chapathi
Temp. of
Heat
No.
plate
Dia.
Thick.
W
Conductivity
kg
kg
Chapathi
Capacity
Temp.
o
m
o
W/m. C
m
-3
C
* 10
(Tp)
(Dc)
* 10
(Initial)
(Final)
o
C
-3
(Wheat Flour)
kJ/kg oK
(xc)
(QTc)
Sensible
Latent
Heat
heat
(Q2c)
(Q3c)
(kc)
(W1)
(Wc)
(Tc)
(Cpc)
1
210
149
1.66
104.88
119.35
0.3751
0.0348
0.02812
116
1.83
2
213
148
1.59
122.74
115.34
0.3555
0.0336
0.0271
118
1.83
3
225
152
1.50
99.00
111.83
0.3035
0.0326
0.0263
120
1.83
66
Table 2.9: Complete Heat Balance on the Chapathi Baking Oven.
S.No.
Description
Contribution
(W)
Percentage
%
1
Total heat absorbed by Chapathi, QTc
236.25
100.00
2
Sensible heat absorbed by Chapathi, Q2c
85.22
36.07
3
Latent heat absorbed by Chapathi, Q3c
151.03
63.93
Basis: Heat transferred to a single Chapathi
67
Table 2.10: Estimation of Thermal Efficiency of the Chapathi Baking Oven.
Sensible Heat Q2c, kJ:
=10,380.00
Latent Heat Q3c, kJ:
= 20,761,30
Total Heat QTc, kJ:
= 31,141.30
Calorific value of LPG Q1, kJ/kg
= 60,814.90
Thermal efficiency of the Chapathi machine (QTc/Q1)*100
= 51.12%
Basis: 400 Chapathi produced by the machine per hour
68
Photograph 1A
Chapathi sheeting unit
69
Photograph 1B
Chapathi machine
70
Sheeting Unit
Sheeting Unit
Diverter - 2
Diverter - 2
Hot Plate - 1
Hot Plate - 1
Gas Burner
Gas Burner
Diverter - 1
Diverter - 1
LPG Cylinder
LPG Cylinder
Gear Box
Gear Box
Motor
Motor
Hot Plate - 2
Hot Plate - 2
Elevation
Elevation
Drawing Not to Scale
Fig. 2.1: Chapathi Machine
Figure - 1: Chapathi Making Machine
Cutter Roller
Return Conveyor
Cutter Roller
Improved Pneumatic extruder
Return Conveyor
Dusting Sub-Assemly
Improved Pneumatic extruder
Dusting Sub-Assemly
Main Drive
Main Drive
Diverter / Chutes
Circular Moving cutter
Diverter / Chutes
Circular Moving cutter
Fig. 2.2: Chapathi Sheeting Unit
Figure - 2: Chapathi Sheeting Device
Top Cover Plate
Quick Fix Coupling
Top Flange
Bolt / Nut
Gasket
Conical Vessel
Gas Deflector
Gasket
WHEAT DOUGH
Bottom Flange
Bottom Cover Plate
Plates (For varying the thickness of sheet)
Note: Working Pressure of the cylinder 6 ksc
Fig. 2.3: Pneumatic Extruder
Top Flanges/ Cover Plate
END VIEW
Slit 1.5 * 180 mm
Sliding Piston
AI
R
Dough
IN
LE
T
Cylindrical Vessel
Extruded sheet, 1.5 mm thick
Strips / Bottom slit plate
ELEVATION
Note: Working Pressure of the cylinder 6 ksc
Fig. 2.4: Improved Pneumatic Extruder
Dusting Sub-Assembly - 2
Cutting Roller
Tube / Rotary Brush / Sieve
Return Conveyor
Dusting Sub-Assemly - 1
Sprockets / Antifriction Bearings
Geared Motor
Roller Chain
Frame
Slat Cutter Assembly
Chain Conveyor
Fig. 2.5: Dusting and Cutting Device
Diverter - 2
Sheeting Unit
Hot Plate - 1
Gas Burner
Outlet chute
Diverter - 1
Oiling device
Diverter - 2
Sheeting Unit
Hot Plate - 1
Transfer chute
Gas Burner
Outlet chute
Diverter - 1
Oiling device
Gear Box
End View
Motor
Transfer chute
Hot Plate - 2
Elevation
Gear Box
End View
Motor
Hot Plate - 2
Plan
Elevation
Chapathies
Inlet chute of sheeting unit
Outlet chute
Plan
Chapathies
Inlet chute of sheeting unit
Figure - 3: Chapthi Baking Unit
Outlet chute
Fig. 2.6: Chapthi Baking Unit
Food was rich in flavour and taste in India in the first few centuries
AD. Rice was converted into many appetizing foods. The appam was a
pancake baked on a concave circular clay vessel and a favored food
taken soaked in milk. The other forms of shallow pan-baked snack were
Dosa and Adai, both based on rice. The Dosa is now made by fermenting
a mixture of “rice and black gram” overnight before baking, and the Adai is
a mixture of almost equal parts of rice and no less than four pulses,
ground together before shallow baking.
Dosa is very popular in India and many different varieties of Dosa
are prepared. The tosai (Dosa i) is first noted in the Tamil Sangam
literature of about 6th century AD (Achaya, 1994). It was then perhaps, a
pure rice product, shallow-fried in a pan, while the Appam of similar
vintage was heated without fat on a shallow clay chatti (pan). The Dosa of
Tamil Nadu is soft, thick product while that of Karnataka is thin, crisp and
large. It is frequently stuffed with a spiced potato mash to yield the
popular masala-Dosa. The Dosa is now made by fermenting a mixture of
“rice and black gram” over night before baking, and the Adai is a mixture
of almost equal parts of rice and no less than four pulses, ground together
before shallow baking.
The laws, which govern heat transmission, are very important to
the engineers in the design and operation of food processing equipments.
The successful operation of equipment component such as turbine blade
and walls of the combustion chamber of gas turbine depends on the
77
possibility of cooling certain metal parts by removing heat continuously at
a rapid rate from the surface. In every branch of engineering heat transfer
is encountered which can be solved by an analysis based on the science
of transport phenomena (heat, mass and momentum transfers).
Literature survey
the need for mechanization with the emphasis on hygiene with reduced
processing cost for the Indian food machinery manufacturers to be
competitive in the global market (Ramesh, 2004).
The Central Food Technological Research Institute at Mysore
(India) has developed formulations for instant Dosa mix, incorporating
machine-ground cereal and pulse flours, baking soda and acid ingredients
such as tamarind, citric acid and soured buttermilk. Formulations for rice,
wheat and millet Dosa are given elsewhere (Anon, 1976). Bureau of
Indian standards has formulated a standard for Dosa mix which contains
rice, black gram, flour, NaCl, sodium bicarbonate and citric or tartaric acid
(ISI, 1983). Instant mixes of traditional food products (including Idly, Dosa
and Medu Vada) based on blends of “rice and black gram” are becoming
increasingly popular. Due to high price of black gram, there is a risk that
some manufacturers may replace some of the black gram in their
products by cheaper materials such as ragi, kidney bean etc. A study
based on modified volumetric bromide/bromate method has been used to
analyze the compositions of such blends, based on the difference in the
pentosan contents of “rice and black gram” (Paradkar et al., 2002). A
78
convection type cylindrical dryer was evaluated for drying of soy-cereal
blended slurry to produce an instant soy-Dosai mix. The studies have
been carried out for the development of instant Dosa max using soyDosai mix and dried for a duration of 12 h (Patil et al., 2001).
Dosa is a fermented food prepared from a 2:1 mixture of “rice and
black gram” flour. White sesame seed was incorporated into Dosa to
replace 5-20% of the flour and enrich the S-amino acid level thereof. The
15% sesame-supplemented Dosa was most acceptable organoleptically
and had increased levels of S-amino acids, especially methionine,
compared to plain Dosa (Geetha et al., 1982). A few Indian traditional
foods based on raw soybean flour such as ‘Dosa’ and 'Vada' were
prepared, to study the trypsin inhibitor activity
(Manorama et al., 1982).
Nutritional problems associated with cereal grains; fermentation of cereal
grains/meals were studied. Further use of fermented cereals in foods
such as: rice-based fermented foods (idli, Dosa, anarshe, dhokla, miso,
puto, sierra or dry rice, lao-chao, ang-kak); wheat-based fermented foods
(soy sauce or shoyu, jalabies, kurdi, kushik, tarhana, kishk); corn-based
fermented foods (banku, ogi, chicha, kaanga-kopuwai); sorghum-based
fermented foods (injera, kisra, ogi, bogobe, feni, ambali); and fermented
beverages are discussed (Chavan et al., 1989). Studies on the processing
of millet for food uses are reviewed, including pearling or debranning,
preparation of chapattis, Dosa, vermicelli or noodles, flaking for soft
cooking and popping or puffing of millets. Effects of processing on
chemical
composition,
moisture
content,
palatability
and
cooking
79
characteristics
of
the
products
and
differences
in
processing
characteristics of sorghum are mentioned (Desikachar, 1977).
Roti (dough balls flattened and roasted on pan), Dosa and
vermicelli were prepared from unconventional sources such as (i) maize,
(Zea mays), (ii) sorghum (Sorghum vulgare) and (iii) bajra (Pennisetum
typhoideum) flour. Water needed for making dough, baking time, moisture
in baked roti, chewing characteristics and storage (24 h) quality were
assessed for roti (Raghavendra Rao et al., 1979). Effect of substitution of
kidney bean (rajmah) meal from other legumes in traditional Indian
processed foods were assessed (Sarojini et al., 1996). The red kidney
bean variety was dehulled and split to form dhal and foods made with dhal
were Dosa (Dosai), vada, fried nuts, curries with vegetables, those made
with meal were sev, muruku, bajji, bonda and pakoda, and those made
with the composite flours were pulka, puri and chapatti. Amaranth grain
was used as pure flour, flour composites (with wheat or rice flours) or
popped grain to prepare various traditional Indian products. Products
evaluated were chikki, laddoo, a snack mixture, a breakfast cereal,
porridge, Dosa, chapati/roti, poori and pulka. (Sarojini et al., 1996). Ten
cereal-based Indian food preparations were investigated for the rate and
extent of in vitro starch digestion. Foods tested included semolina idli and
upma, rice flake upma, rice roti, ragi roti, poori, pongal, idli, Dosa and
chapathi, with and without their accompaniments (cooked dhal, chutney
and potato palya) (Sharavathy et al., 2001).
Supplementation of ragi based products with whey protein
concentrate (WPC) to enhance their nutritional profile and formulation of
80
ragi based products to enhance their nutritional values are discussed
(Suchitra et al., 2003). High nutritional value of rice germ, its incorporation
into common Indian foods was investigated. Raw rice germ incorporated
into various confectionery products made with boiled sugar solution and
flavorings (pongal, sweet ball and sweet cake), and defatted rice germ
flour could be incorporated into Dosa (made of rice, black gram and salt)
at up to 20% of rice flour (Vasan et al., 1982).
Some aspects of indigenous fermented foods, many of which are
almost unknown outside the Orient, are reviewed (Ko-Swan-Djien, 1982)
with special attention given to the microorganisms and their role in the
fermentation process. Some indigenous fermented foods are studied
according to the microorganisms involved in the process. Certain cerealbased fermented foods and beverages produced in different parts of the
world, in relation to techniques used in their manufacture, consumption
patterns, nutrient contents and sensory properties. The aspects studied
include: biochemical changes that occur during cereal fermentation for the
preparation of; indigenous rice-based fermented foods (idli, Dosa,
dhokla); traditional wheat-based products (soy sauce, kishk, tarhana,);
traditional corn-based fermented foods (ogi, knekey, pozol); traditional
foods prepared by sorghum fermentation (injera, kisra); traditional cerealbased fermented beverages (beers, sake, bouza, chicha, mahewu, boza);
and
new
cereal-based
probiotic
foods
(Blandino
et
al.,
2003).
Saccharomyces cerevisiae enrichment in combination with the natural
bacterial flora was studied for standardizing Dosa fermentation. Batter
types containing soybeans and mung bean were compared with
81
conventional black gram product (Soni et al., 1989). The prevalence of
organisms in fermented foods in different seasons and microbiological,
biochemical and nutritional constituents in fermented foods such as
Punjab warri, papadam, bhallae, vadai, idli and Dosa were studied at the
beginning and the end of fermentation (Soni et al., 1990). Changes in pH,
reducing sugars, soluble proteins, total N, amylases, proteinases and
microbial load, during fermentation of Dosa batter were monitored. Batter
was made by overnight soaking of equal quantities of rice and decuticled
black gram (separately), grinding, and mixing them, before 24 h auto
fermentation or fermentation using an inoculation of a previous batter
(Soni et al., 1985). A number of fermented foods, mainly traditional ones,
were described, and studies on interrelationships of their component
microorganisms.
Foods
involving
an
acid
fermentation,
covering
sauerkraut, Indian idli and Dosa, sour dough breads and related
fermentations, Nigerian ogi and gari, Kenkey-fermented maize dough
balls of Ghana, Mexican pozol, Russian kefir, and vinegar fermentation
(Steinkraus, 1982). Cheese, fermented cereal-legume batters (idli and
Dosa), chocolates, fermented vegetables, sprouted legumes, wine, curd
and processed meat and fish products were analyzed by HPLC to
determine polyamine composition (Vasundhara et al., 1998).
Digestibility indices (DI) of ragi-based preparations (dumpling, roti,
puttu and Dosa (with/without accompaniments)) were determined by
measuring rate of starch hydrolysis in vitro, and thereafter comparing the
same by replacing ragi with other cereals (rice, wheat or jowar) in similar
preparations are discussed (Roopa et al., 1998).
82
In the context of implementation of a HACCP system for monitoring
of pasteurization of fresh filled pasta, studies were conducted on
determination of critical limits of the 2 factors controlling pasteurization:
time and temperature (Zardetto, 1999).
traditional foods. Though a good amount of work has been reported on
thermal conductivity of biological materials, practically no data available
for baked Dosa and Dosa batter. The work on the process for the
preparation of quick cooking rice with increased yield, reduce processing
cost has been reported (Ramesh. 2000,)
two principal areas of technical creative activity are closely interrelated.
The designer has to keep in mind the product designed by him to be
manufactured in the most economical way. Apart from the knowledge
manufacturing aspects, he must be in touch with the consumer needs to
understand their requirement. The official regulations, national codes,
safety norms are to be given due consideration and these often play a
decisive part in determining design.
The machine design can be broadly classified into three categories
as adaptive design, developmental design and new design. In adaptive
83
manufacture, or to use a new material. In developmental design, a
designer starts from an existing design but the final result may differ quite
markedly from the initial product. This design calls for considerable
scientific training and design ability. New design, the one, which, never
existed before, is done by only a few dedicated designers who have
personal qualities of a sufficient high order. Considerable research,
experimental activity and creative ability are required for this. A
limitations and practicability of various production methods will help in
making a successful design of a machinery. Machine design involves the
knowledge of strength of materials, properties of materials, metallurgy,
production techniques, theory of machines, applied mechanics etc.
The design process could be summarized as a) the aim of the
design, b) preparation of the simple schematic diagram, c) conceiving the
shape of the unit/ machine to be designed, d) preliminary strength
calculation, e) consideration of factors like selection of material and
manufacturing method to produce most economical design, f) mechanical
design and preparation of detailed manufacturing drawing of individual
components and assembly drawing. The selection of the most suitable
materials for a particular part becomes a tedious job for the designer
partly because of the large number of factors to be considered which have
84
bearing on the problem and partly because of the availability of very large
number of materials and alloys possessing most diverse properties from
which the materials has to be chosen. With the development of new
material, a good knowledge of heat treatment of materials which modifies
the properties of the material to make them most suitable for a particular
application is also very important. The property of corrosion resistance is
obtained by adding chromium or by adding chromium and nickel together
and stainless steel is manufactured in electric furnaces. Selection of
material for food processing machinery is an added task for the designer.
For most of the food application stainless steel is the preferred material as
the food material contains large amount of moisture and product is for
human consumption, hence needing hygiene. In certain cases, where
acid foods are handled, a special variety of stainless steel having very low
carbon content, which has oxidation-resistant property, is recommended.
The thermal and physical properties of a few fruits and vegetables
studied are co-efficient thermal expansion, thermal conductivity, specific
heat, specific gravity, electrical conductivity and magnetic property. The
various mechanical properties are strength in tensile, compressive, shear,
bending, torsion and fatigue as well as impact resistances.
Justification
As already mentioned, design of machinery for Indian traditional
foods is new and a specialized area. Very few organizations are involved
in design and development of such food processing machinery, which fall
into the category of new design and involves extensive research and
85
experimentation. Most of the foods processing machinery available in the
country are imported from other countries and most of them are for
processing of fruits, vegetables, bakery products, confectionery and oils.
For the largescale production of Dosa (360 Nos./h), as required by
industrial and military canteens, a continuous automatic Dosa -making
machine has been designed. As the value of time is increasing day by
day the demand for the ready-to- eat traditional foods is also increasing.
Some traditional Indian foods such as Dosa and idli are becoming more
popular. Though the basic kitchen technology for the production of these
traditional foods is known, considerable research and development efforts
are required to translate such technology to the large-scale production
level. This requires major inputs from food engineers and technologists.
The objective of the present work is to design and develop
machineries for Indian traditional foods incorporating the different
branches of engineering such as thermal, mechanical, chemical, electrical
and electronic and food engineering. The understanding of the physical,
thermal and engineering properties of foods is very important for the
design of any food-processing machine. Integration of the equipment
developed with the technology of food processing is also considered. In
the present work the design and development of Dosa making machine
with the standardization of respective food ingredients for conventional
and instant Dosa batter is takenup. The study also involves the heat
transfer studies in the preparation of Dosa, structural changes that takes
place during baking, the standardization of conventional batter and
standardization of the instant batter dry mix for use on this machine.
86
Section 3.2.0: Materials and methods
Oil
Commercially available vegetable oil (groundnut oil/sunflower oil) is
used during the baking of Dosa and the quantity of oil used per Dosa
is around 5 ~ 10 g.
Rice
Commercial grade raw rice was purchased from the market and
had initial moisture of 11%. The same rice was used for the preparation of
conventional batter as well as the dry instant batter.
Black gram
The split black gram was purchased from the local market for the
preparation of the conventional batter as well as dry instant batter.
Preparation of Dosa batter
Conventional Batter
Conventional batter is prepared by grinding soaked rice and urd
dhal
(blackgram
dhal)
with
water
in
known
proportions
for
a
predetermined time to get the required fineness. The batter is allowed to
auto-fermentation for 15-17 h in a closed stainless steel vessel. A wet
87
grinder of 15 liter of volume, having a pair of stones (one moving stone
and while the other stationery) having a stationery wooden diverter to
guide the material into the grinding zone. A stainless steel cover is fixed to
the main frame to avoid spillage of the ground material and to make it leak
proof. The wet grinder has a capacity of 10 l of wet material. The rotating
stone is driven by a geared motor having a rotational speed of 300 ~ 400
RPM. The batter is ground for 20 minutes and water is added during
grinding as and when required. The operator discharges the ground
material by tilting the vessel.
Fermentation of Batter:
The Dosa batter ingredients, namely “rice and black gram” was
soaked in water with a ratio of water to grain at 3:1 for 4 hours in a
measuring jar. The expansion of the soaked grain was measured at an
interval of 1 h. The ingredients are ground for 20 min using a domestic
wet grinder and the density of the ground batter was measured to be
1.340 g/cc. The batter is then allowed to ferment for about 17 h at a
controlled temperature ranging from 25 ~ 40O C in a drying oven and
increase in volume of the batter was observed after fermentation. The
conventional batter fermented at 40°C had all the characteristic flavour of
the Dosa batter and the increase in volume of the batter after fermentation
was more than double.
88
Instant Batter Mix Powder
The following are the different approaches that has been attempted to
formulate the instant Dosa batter.
1. Hot air drying (using tray dyer) of the conventional batter
2. Freeze drying of the conventional batter.
3. New formulation using different ingredients.
1. Hot Air Drying of the Conventional Batter
The conventional batter having ingredients such as “rice and black
gram” in the ration of 4:1 was spread on the trays (after fermentation for
over 16 h) of the tray dryer and dried for over 4 h at a temperature ranging
from 40 ~ 45°C. The dried material was scraped from the trays and
ground/powdered fine using a tabletop plate grinder. In order to evaluate
the powder, it was mixed with water in the ratio of 2:1 (water to solids) and
stirred well using a hand held blender and rested for 15 ~ 20 min.
2. Freeze Drying of the Conventional Batter
“Rice and black gram” in the ration of 4:1 was ground for 120 s
using a tabletop grinder. The batter was allowed for fermentation of 16 h
in a temperature controlled drying oven. The fermented material was then
transferred to the trays of the freeze dryer. The batter gets frozen to a
temperature of -25°C and dried at a temperature of +20°C keeping the
vacuum level at 250 microns and the material was freeze dried for 16 h.
The dried material was scraped out from the trays and ground/powdered
fine using a table top plate grinder. In order to evaluate the powder, the
89
batter powder was mixed with water in the ratio of 2:1 (water to solids)
and stirred well using a hand held blender and rested for 15 ~ 20 min.
3. New Formulation Using Different Ingredients
In this approach the formulation based on rice, black gram, bengal
gram flour and maida is used. The chemicals such as calcium carbonate,
sodium acetate and citric acid are used to bring the batter attributes such
as the hole density (characteristic holes of Dosa), flavour, texture etc. The
above formulation is blended with water in the ratio of 1.5: 1 (water to
solids) and stirred well using a hand held blender (make: Braun, type
4169, made in Mexico) and soaked for 30 min.
Fermentation of the batter was carried out at a controlled
temperature ranging from 25 ~ 35OC in a drying oven for about 15 ~ 16 h.
A temperature controller of (EAPL make, model No.TX7-D) was used to
regulate the temperature inside the drying oven which had a ‘K’ type
thermocouple with sensitivity of ±5OC.
A digital temperature indicator (Model – TFF 200, Make – EBRO,
Germany, PT-100, Range: -50 to 200 •C) was employed to measure the
temperature of the hot plate as well as the product. The temperature
indicator had a resolution of 0.1•C with a least count of 0.1 •C.
90
Dosa were baked on the hot plate by discharging a known amount
of batter of predetermined consistency (Bhattacharya and Bhat, 1997).
The top of the Dosa was covered by an asbestos plate of 0.005-m (5mm)
thick to prevent radiation from the stainless steel hood and to allow Dosa
baking by conduction alone. The probe of the temperature indicator was
positioned through a hole at the center of asbestos disc to measure the
temperature of the product top surface (Venkateshmurthy et al., 2005).
Thermal conductivity was calculated from these test results by using
appropriate terms in equation (9) and (10).
Determination of Product Emissivity
The Dosa batter was spread on the asbestos sheet and transferred
on to the hot plate with another asbestos insulation at the bottom (to avoid
conduction heat transfer). The batter was baked by radiation alone from
the hood of the machine. The temperature of the hood was recorded.
Emissivity was calculated from these test results by using appropriate
terms in equation (9) and (10).
Determination
of
Microstructure
using
Scanning
Electron
Microscope
The baked Dosa prepared using different hot plate materials were
viewed under the scanning electron microscope (model -Leo 435 VP of
91
Leo Electron Microscope Limited, Cambridge, UK) at a magnification of
500.
The conventionally prepared batter was used for the preparation of
Dosa and the thickness of the Dosa was in the range of 2~4 mm. Dosas
were prepared using hot plates of different materials such as cast iron,
stainless steel, steel and Teflon coated aluminum and the Dosas were
viewed under the electron microscope to evaluate the hole density.
Determination of the Temperature Profiles:
Dosa batter was spread to uniform thickness on to the hot plate,
maintained at uniform temperature. A cylinder with a hole for insertion of
the thermocouple was used for measuring the temperature at different
depths of the Dosa batter. In order to study the temperature profiles of the
Dosa, thermocouple was inserted into the Dosa at different depths
ranging between 0.0005–0.0020 m (0.5~2.0 mm) with the help of
slip/thickness gauge and the raise in temperature was observed with time
ranging between 30–120 s.
Sensory Analysis:
Sensory characteristics of the Dosa prepared on the Dosa -making
machine were tested among 10 trained panelists from Department of
Sensory Science using quantitative descriptive analysis.
92
The study was also conducted to evaluate the quality of Dosa
prepared using hot plate of different materials such as cast iron, mild
steel, stainless steel and Teflon coated aluminium.
Section 3.2.3 Measurement of Thermal properties
Thermal diffusivity:
Experimental set-up
The experimental set-up is shown in Fig. 3.1. It consists of a
copper tube of 2.25-inch diameter and a length of 9 inch. Copper, being
rigid and having high thermal conductivity value facilitates high heat
transfer, thus reducing the time taken to reach steady state. The
apparatus based on the transient heat transfer conditions require only
time-temperature data. The apparatus consists of an agitated water bath
in which the copper tube-containing Dosa batter was immersed.
Thermocouples were soldered to the outside surface of the cylinder
monitoring the temperature of the sample at radius R. A thin
thermocouple probe indicated the temperature at the center of the
sample. The bottom end of the copper cylinder is fixed with a cap made of
Teflon (alpha = 4.17 * 10-3 ft2 / h) and filled with the Dosa batter of known
weight. The cap made of Teflon material is used to close the top end of
the copper tube and the thermocouple is inserted to full immersion to
insure proper radial positioning. The cylinder is placed in the agitated
water bath and temperatures of the wall and center temperature of the
copper cylinder (Dosa batter temperature) are recorded until a constant
rate of temperature rise is obtained for both inner and outer
93
thermocouples (Table 3.1). A plot of wall temperature of copper cylinder
and the center temperature of Dosa batter temperature is as shown in the
graph at Fig. 3.2.
For the appropriate dimensions for the cylinder, Dickerson (1965)
showed that the maximum temperature difference (T1–T2), or the
establishment of steady state takes place when,
αd θ
R 2 〉 0.55
(1)
Knowing the approximate range of ‘αd’ of the Dosa batter and considering
a reasonable experimentation time ‘θ’ for collecting the time-temperature
data, appropriate radius of the cylinder ‘R’ was determined to be an inch.
With Teflon ends, as good heat insulator, a length of 9 inches suitable for
water bath was considered (Dickerson, 1965).
Under the constant temperature rise, the Fourier equation for the
case when only radial temperature gradient exists, the thermal diffusivity
of the Dosa batter can be evaluated by using the equation
αd = A R2
4 (T1 − T2 )
(2)
where, αd, Thermal diffusivity of Dosa batter, m2 / s; A, The constant rate
of temperature rise,
O
C/ min; R, Radius of the copper cylinder, m; T1, The
out side surface temperature of the copper cylinder, OC; T2, Temperature
of the batter inside the copper tube, OC; Θ, Experimentation time, Min.
Experimental Procedure
To evaluate the approximate vales of the thermal diffusivity and the
specific heat of the Dosa batter, the mass fractions of the composition of
the Dosa batter such as carbohydrate, protein, fat, ash and the moisture
94
of the ingredients were noted from the literature. The main ingredients of
the Dosa batter are the Rice and Black gram and the composition of the
Rice and the Black gram is given in Table 3.2.
The empirical predictive equations developed by Dickerson (1969)
and Sweat (1986) for the evaluation of the specific heat and thermal
conductivity respectively were used for the estimation. The following are
the predictive equations:
Specific Heat (Cpd)
C pd = 1.42 mc + 1.549 m p + 1.675 m f + 0.837 ma + 4.187 mm
(3)
where, m is the mass fraction: while the subscripts are c, carbohydrate;
p, protein; f, fat; a, ash; and m, moisture.
Thermal Conductivity (kdb)
k db = 0.25 mc + 0.155 m p + 0.16 m f + 0.135 m a + 0.58 m m
(4)
where, m is the mass fraction: while the subscripts are c, carbohydrate;
p, protein; f, fat; a, ash; and m, moisture.
Based on the above predictive values, the experimental duration is
fixed to be around 60 min. The known weight Dosa batter (conventional
and instant mix with known added moisture) was transferred into the
copper tube whose bottom end is closed by a Teflon cap. The copper
tube was closed on top by another Teflon cap and a thermocouple was
inserted to the full depth of the product (Dosa batter). An insulated water
bath was used for the experimentation. The water bath having a known
95
quantity of water was maintained at a predetermined temperature ranging
from 60 ~ 80°C and the temperature of the water was controlled by a
temperature controller having a least count of 0.01°C.
The time-
temperature data of the surface of the copper cylinder and the core
temperature of the Dosa batter were recorder at a time interval of 2 min.
Thermal diffusivity of Dosa batter was estimated by substituting
appropriate values obtained during the experimentation in the equation (2)
considering Rd= 1.125 inch. The average value of the thermal diffusivity
(Table 3.3) was found to be 1.39 m2/s.
Specific heat of Dosa batter was evaluated by equating the heat
lost by the water bath (q1d) to that of the heat gained by batter (q2d). The
drop in temperature of water in the bath was in the range of 0.15 ~ 0.20
°C. The specific heat of the Dosa batter was found to be 3.12 kJ / kg OC,
(Table 3.3) and the predictive and the experimental values are shown in
Table 3.4.
The average density of the Dosa batter was found to be 1108.70
kg / m3. The thermal conductivity of the Dosa batter was estimated by
substituting the values of the thermal diffusivity (αd), specific heat (Cpd)
and the density (ρd) of Dosa batter in the equation; αd = kdb / ρd Cpd. The
average value of the thermal conductivity of the Dosa batter is 0.48 W / m
O
C, (Table 3.3). The predictive and the experimental values of the thermal
conductivity are given in Table 3.4.
96
1. Dosa Machine
Fig. 3.3 represents a Dosa machine wherein; the hot plate is driven
by a set of sprockets and chain (or a set of worm and worm wheel) which
are mounted on a shaft housed in anti-friction bearings. The sprocket
assembly is driven by the geared motor through a roller chain. The
dispenser assembly consists of a pump with solenoid valve attached to a
receiver with a bypass line. The device also carries a curry and/or chutney
dispenser for discharging the same on to the cooked Dosa. The oiling
assembly consists of drip nozzle and hopper. Oiling unit is located after
the spreader assembly. Oiling is done in two stages during the process of
Dosa making (i) for initial greasing for uniform heat transfer and (ii) in the
form of a spray for roasting the Dosa. The baked Dosa are scraped, rolled
and discharged by a straight edged curved blade and collected in a tray.
All the above-mentioned assemblies are mounted on a channel frame,
which is insulated around the burner and covered on all the sides. The
whole assembly is mounted on swivel castors for easy movement of the
device to the required place. Materials like Steel / Stainless Steel / Steel
coated with PTFE / Brass are used in the fabrication of the device.
2. Improved Dosa Machine
Fig. 3.4 represents an improved device for spreading, baking and
scraping of Dosa and other similar products (improvements are shown in
different colour). A reduction gearbox drives the vertical shaft, which in
97
turn drives the hot plate. The accessories such as batter cum oil
dispenser, floating spreader assembly curry dispenser and floating
scraper assembly and the scraper are provided above the hot plate. The
device is provided with electronic controls for varying the rotational speed
of the hot plate, the solid-state timer for controlling the quantity of the
batter and a temperature controller for controlling the hot plate
temperature.
3. Auto–Discharge Assembly for Dosa
For automatic discharge of Dosa, a mechanism has been designed
as shown in Fig. 3.5 without manual intervention hygienically. It
comprises of a radial scraper which is rested on the hot plate of the Dosa
making machine for scraping the baked Dosa and the radial scraper is
provided with a radial diverter for folding and guiding the Dosa on to the
chute to be transferred to the collecting tray, and the holding bar holds
down the radial scraper as well as the radial diverter, firmly on to the hot
plate and the holding bar in turn is held in position by a set of fasteners,
all the parts are made of stainless steel.
4. Energy Balance
Theoretical heat absorbed by the baked Dosa involves the sensible
heat of the solids plus the water contained in the batter, the latent heat of
evaporation of water during baking. The sensible heat of solids and water
has been estimated to be 8307.80 kJ and the latent heat of evaporation of
water is around 22,994.93 kJ. The total heat required per Dosa was
estimated to be the sum of sensible heat and the latent heat and found to
98
be 31,302.72 kJ. From the experiments it was noted that the residence
time for baking of Dosa is around 120 s and the capacity of the Dosa
making machine is 360 Nos/h.
The machine has a circular liquid petroleum gas (LPG) burner,
having all the required operational and safety accessories such as mixing
tube, pilot lamp, solenoid etc. From the large-scale trials of the machine,
the actual consumption of the fuel (LPG) was found to be 60,814.90 kJ
(1.25 kg of LPG/h) and the thermal efficiency of was found to be 51.47%
(Table 3.5).
Commercially available LPG a blend of butane and propane in the
ratio of 60:40 is used as heat source. From the theoretical calculation the
requirement of the LPG for supplying the required heat to the hot plate is
estimated to be around 643 g, considering the calorific value of the LPG
as 48,651.92 kJ.
It was reported that 30 kgs of air is required for
complete combustion of the LPG. The loss of heat is to the tune of
29,512.18 kJ and is accounted for the radiation loss in the oven.
99
Dosa Machine
The Dosa machine shown in Fig. 3.3. It represents the device
which comprises of: a geared motor, spreader assembly, revolving hot
plate assembly, circular burner with accessories, scraper, oiler, curry
dispenser, main frame with necessary insulation, batter pump attached to
a vessel, a solenoid valve, sprocket assembly, an electronic timer, an
electrical panel board, a temperature indicator, a hood with sight glass,
antifriction bearings, a base support, a pivot bearing, and a rotatable
vertical shaft.
The hot plate is driven by a set of sprockets and chain (or a set of
worm and worm wheel), which are mounted on a shaft housed in antifriction bearings. The sprocket assembly is driven by the geared motor
through a roller chain. The dispenser assembly consists of a pump with
solenoid valve attached to a receiver with a bypass line. The device also
carries a curry and or chutney dispenser for discharging the same on to
the cooked Dosa. The oiling assembly consists of drip nozzle and hopper.
Oiling unit is located after the spreader assembly. Oiling is done in two
stages during the process of Dosa making (i) for initial greasing / for
uniform heat transfer and (ii) in the form of a spray for roasting the Dosa.
The baked Dosas are scraped, rolled and discharged by a straight edged
curved blade and collected in a tray. All the above-mentioned assemblies
are mounted on a channel frame, which is insulated around the burner
100
and covered on all the sides. The whole assembly is mounted on swivel
castors for easy movement of the device to the required place. Materials
like Steel / Stainless Steel / Steel coated with PTFE / Brass are used in
the fabrication of the device. All the necessary electrical parts of the
device are housed inside the panel board attached to the main frame. The
batter is prepared by grinding “rice and black gram” with sufficient quantity
of water in known proportion to a predetermined time to get the required
fineness. The batter is allowed to ferment for 8-10 hrs in a closed
stainless steel vessel. The prepared batter is charged into a vessel
connected to the feed side of the screw pump. The pump with a solenoid
valve is fitted in the discharge pipeline and the electronic timer, controls
the intermittent batter deposition on the hot plate in predetermined
quantities and appropriate time interval. Batter is spread into an elliptical
disk of uniform thickness by the spreading device as the hot plate rotates.
Automatic oiling device sprays a very thin coat of edible oil on the
spreadsheet of batter. This will not only improves the organoleptic
properties of the Dosa but also helps in rapid, uniform heat transfer and
baking of the Dosa. Depending on the water content of the batter, the
baking time is adjusted either by the sprocket train / worm and worm
wheel or by an electronic inverter. In the event, the Dosas needed to be
filled with curry, the material from the curry dispenser can be filled on the
Dosa before they are rolled and discharged. The baked Dosas are
scraped, rolled and discharged by a scraper and collected in a tray.
During the operation, the device was observed to have the following
drawbacks:
101
1. The hot plate has the tendency to distort during the process of heating
and operation.
2. The distortion of the hot plate produces non-uniform thickness of the
product.
3. Due to distortion of the hot plate the scraper needed flexibility to move
vertically and rotate as well.
4. The screw pump fitted on the battery discharger needs regular
attention and is very costly.
5. There is no water cleaning arrangement during the process of
operation.
2. Improved Dosa Machine
Fig. 3.4 shows an improved device for spreading, cooking / baking
and scraping of Dosa and other similar products. It consists of a geared
motor, a gear box, floating spreader assembly shown in Fig. 3.6 a
revolving hot plate assembly, circular burner with accessories, floating
scraper assembly as shown in Fig. 3.7, batter cum oil cum water
dispenser shown in Fig. 3.8, curry dispenser, main frame with cover and
necessary insulation, LPG solenoid valve, an electronic timer, an
electrical panel board, a temperature controller with sensor, a hood with
sight glass, a set of castors, a set of bearing supports for hot plate, a
mechanical / digital electronic counter, a batter container, an oil container,
water tank, an AC drive, and rotatable vertical shaft.
The improved device comprises, a main frame, having a set of
castors, for easy movement of the improved device. Rotating horizontal
102
hot plate assembly, is driven by a geared motor, and a gear box, and an
AC drive, supported by a set of bearings supports. The hot plate is heated
by a circular LPG burner with its accessories and the temperature of the
hot plate is regulated by a temperature controller with sensor, through a
LPG solenoid valve. The batter cum oil dispenser, is timed by an
electronic timer, and the thickness of the Dosa in controlled by a floating
spreader assembly. The water tank and the batter cum oil dispenser, is
mounted on the floating spreader assembly. The floating spreader
assembly and floating scraper assembly are mounted on the main frame.
A panel board is mounted on the main frame, for easy operation of the
machine and the panel board houses the AC drive for controlling the
speed of the hot plate and a mechanical digital electronic counter and an
electronic timer. The batter and the oil are contained in the batter
container and an oil container, which is mounted on the batter cum oil
dispenser. A curry dispenser is mounted on the hood with sight glass for
dispensing the curry on to the baked Dosas. The scraper assembly is
fastened to the main frame through a round bar, and a compression
spring is assembled on to the round bar and the straight edged scraper,
rests on the hot plate. The floating spreader assembly, comprises of a set
of square bars fastened to the main frame and the thumb wheels
connects the square bars, a set of compression springs, is placed
between the square bars, the pressure is exerted by the thumb wheel, on
to the hot plate. The batter cum oil dispenser is used for the dispensation
of the batter and oil simultaneously. The batter cum oil dispenser consists
of a solenoid, to actuate the valve, for dispensing the batter and oil. A
103
water tank is mounted below the solenoid and the valve and the opening
and closing of the batter cum oil dispenser is by an electronic timer.
3. A Device for Automatic Discharge of Dosa
The device for automatic discharge of Dosa is as shown in Fig.
3.5. The invention provides a device for automatic discharging of Dosa
and other similar Indian traditional foods comprises of, radial scraper,
which is rested on the hot plate of the Dosa making machine for scraping
the prepared Dosa and the radial scraper is provided with a radial
diverter, for folding and guiding the Dosa on to the chute, to be transferred
on to the tray, and the holding bar, holds down the radial scraper and the
radial diverter firmly on the hot plate and the holding bar is held in position
by a set of fasteners, all the parts are made up of stainless steel this
however does not restrict the invention as any other material can be used.
Section 3.3.2: Standardization of Dosa Batter
1. Dosa Preparation Using Conventional Batter
The raw materials, namely, “rice and black gram” were procured
from the local market and the bulk densities were estimated to be around
1.34 l/kg. Different combinations were tried by varying the rice to black
gram ratio for the standardization of Dosa batter. The black gram was
incorporated in the proportion ranging between 15 ~ 35% of rice. The
conventional batter is prepared from “rice and black gram” by soaking in
water, in the ratio of 3 parts of water to 1 of “rice and black gram”. The
104
soaking time was about 4 h and the expansion index of “rice and black
gram” was observed to be in the range of 1.45 to 1.55 and 2.18 to 2.45,
respectively (Table 3.6). The maximum expansion of the grains were
observed in the first hour of soaking with an expansion index of 1.45 for
rice and 2.18 for black gram, only a nominal expansion index of 0.1 and
0.27 for “rice and black gram”, was observed respectively during the rest
of the soaking period of 3 h. The ingredients are ground for 20 min using
a domestic wet grinder and the density of the ground batter was
measured to be 1340 kg/m3. The batter is then allowed to ferment for
about 17 h at a controlled temperature ranging between 25 ~ 40O C in a
drying oven and increase in volume of the batter was observed after
fermentation. The conventional batter fermented at 40°C had all the
characteristic flavour of the Dosa batter and the increase in volume of the
batter after fermentation was more than double.
In order to have the controlled fermentation of the batter, a drying
oven having a temperature controller was used. Increase in the volume of
the batter (Table 3.7) was measured using a measuring jar. Fermented
batter was diluted with water in the ratio of 3:1 (water to “rice + black
gram”) and each kilogram of “rice and black gram” produced 3 kgs of
Dosa batter. It was observed that the viscosity of the rice batter (without
black gram) was measured to be in the range of 172 ~ 209 m.Pa.s. The
viscosity of the fermented batter increased with the increase of black
gram and the viscosity of the Dosa batter (with addition of black gram
ranging between 15 ~ 35%) was in the range of 196 to 2041 m.Pa.s
(Table-3.8).
105
The test Dosas were prepared from the fermented batter using a
conventional hot plate (tava) baking for about 120 s at a temperature
ranging between 180 ~ 190° C. The Dosa was prepared using different
formulations such as the batter with zero black gram and with addition of
black gram ranging from 15 ~ 35% of rice. The baked Dosas were
evaluated for shear strength and colour (of top and bottom sides of the
Dosa). The shear strength of the Dosa was studied both with and without
the application of oil. It was observed that the shear strength of the Dosa
without oil was in the range of 5.77 ~ 8.52 N. It was also noted that the
shear strength of the Dosa baked using oil was slightly less than that
baked without oil indicating less crisp product and was in the range of
5.24 ~ 6.69 N (Table 3.8). It was noted that the shear strength reduced to
2.00 N with the urdh content of 35% indicating soft/less crispier Dosa
(Table 3.8). It was noted that the colour of the bottom side of the Dosa
was of much darker brown as given in (Table 3.8).
2. Dosa Preparation Using Instant Batter
The standardization of the instant batter was made in three
approaches. The conventional batter having ingredients such as “rice and
black gram” in the ration of 4:1 was spread on the trays (after
fermentation for over 16 h) of the tray dryer and dried for over 4 h at a
temperature ranging from 40 ~ 45°C. The dried material is scraped out
from the trays and ground/powdered fine using a table top plate grinder.
In order to evaluate the powder, the batter powder is mixed with water in
106
the ratio of 2:1 (water to solids) and stirred well using a hand held blender
and rested for 15 ~ 20 min.
Dosas were prepared using the above batter on a conventional hot
plate (tava) maintained at 180 ~ 190°C. It was observed that the Dosa
were spongy and
hard. The density of the characteristic holes and
crispiness are comparable to the Dosas made from conventional batter.
The
dried
material
is
scraped
out
from
the
trays
and
ground/powdered fine using a tabletop plate grinder. In order to evaluate
the fresh dried conventional batter powder, the batter powder is mixed
with water in the ratio of 2:1 (water to solids) and stirred well using a hand
held blender and rested for 15 ~ 20 min.
It is believed that the freeze-dried product to be an excellent one
and freeze dried material is normally taken as the reference material. The
Dosa’s were prepared using the above instant batter. It was observed that
the Dosa were spongy and
hard. However, the density of the
characteristic holes and crispness were less comparable to the Dosas
made from the conventional batter.
The formulation described earlier was blended with water in the
ratio of 1.5: 1 (water to solids) and stirred well using a hand held blender
and soaked for 30 min and it was observed that the Dosas were spongy
and hard. The density of the characteristic holes and crispiness were
absent when compared to the Dosas made from conventional batter.
107
3. Effect of Hot Plate Material on Dosa Texture
To study the effect of the hot plate material, Dosa were prepared
using different hot plate materials such as alloy steel, cast iron, stainless
steel and Teflon coated aluminum. The hot plate materials had a thermal
conductivity ranging between 16~51 W/m°C. The Dosa were baked using
the batter prepared conventionally and also with the instant batter mix.
The thickness of the hot plate materials were kept constant at 5 mm and
the temperature of the hot plate was maintained between 180 ~ 190°C
with the baking time of 120s. The Dosas were viewed under the scanning
electron microscope to see the pattern of holes formed in Dosa due to the
evaporation
of
the
moisture
during
the
baking
process.
The
microstructures are shown in Fig. 3.9. It is clearly seen from the figure
that the material such as stainless steel and teflon-coated aluminum had
smaller and uniform structural holes of large numbers as compared to the
cast iron and alloy steel material. This can be attributed to the fact that the
material with higher thermal conductivity has uniform distribution of heat
and also high rate of heat transfer compared to alloy steel and cast iron.
The difference in density of the holes was clearly reflected in better
surface finish of the Dosa prepared using stainless steel and Teflon
coated aluminum hot plate materials.
The sensory analysis was carried out by 10 panelists using
quantitative descriptive analysis. The profilogram as shown in Fig. 3.10
indicates the typical characteristics of Dosa having low value of staleness,
bitterness and sourness, which are the measures of good quality product.
108
The high values of crispness, colour, puffiness, tearing strength are added
attributes to the good quality of the Dosa with an overall score at 11 out of
15 as shown in the profilogram in Fig. 3. 10.
Section 3.3.3: Heat transfer analysis
Theoretical Aspects
The mathematical expression for each individual mode of heat
transfer can be written as
Conduction
qCd = k d . Ad . (Tdb − Tdt )
xd
(5)
where qcd is heat transferred by conduction to the Dosa, kJ; kd the
thermal conductivity of Dosa, W/m •C; Ad the area of the Dosa in contact
with the hot plate bottom, m2; Tdb temperature of the Dosa bottom surface,
which is in equilibrium with the hot plate temperature and is equal to it •C.;
Tdt the temperature of the Dosa top surface, •C and xd the thickness of the
Dosa, m.
Convection
q Fd = hFd . Ad . (TRd − Tdt )
(6)
where qFd is the heat transferred by convection to the Dosa, kJ; hFd
convective heat transfer coefficient of Dosa, W/m2 o K; Ad the area of the
Dosa in contact with the hot plate bottom, m2; TRd the temperature in oC of
the hot air inside the hood: Tdt the temperature of the Dosa top surface,
•
C.
109
Radiation
(
q Rd = Fprd . Ad .σ . T 4 Hd + T 4 dt
)
(7)
Where, qRd is the heat transferred by radiation to the Dosa, kJ; σ the
Stefan-Boltzman constant, W/m2 h k4; THd the hood (refractory surface)
temperature, oC: Tdt the temperature of the Dosa top surface, •C and Fprd
overall coefficient for radiation heat transfer, is given by
Fprd = 1
{1
f prd + (1
ε pd − 1 ) + ( Ad
Ard ) (1
ε Hd − 1)}
(8)
Where, fprd is geometrical factor for Dosa machine; εpd the emissivity of
the Dosa; εHd emissivity of the hood of Dosa machine and Ard area of the
radiating refractory surface, m2.
Derivations and detailed discussions of these expressions are
given elsewhere (McCabe, Smith & Harmot, 1995; Charm, 1971;
Heldman and Singh, 1993; Perry and Green, 1984).
Total heat transferred to Dosa can be written as
QTd = qCd + q Fd + q Rd
(8a)
Considering the baking of Dosa on a rotating hot plate with batter
spread on it, the main mechanisms of heat transfer to the Dosa s are
conduction from the rotating hot plate and radiation from the hood.
Convection heat transfer is not considered, as the air/flue gas flow is too
little. The equation for total heat transferred to Dosa (QTd) can be written
using expressions (5), (7) and (8):
QTd = qCd + q Rd
= kd . Ad . (Tdb − Tdt )
(
xd + Fprd . Ad .σ T 4 Hd − T 4 dt
)
(9)
110
The total heat transferred must be equal to the total heat absorbed
by the product. Considering the gross temperature rise of the product
(sensible heat increase) and the latent heat of vaporization of evaporated
moisture, the total theoretical heat absorbed by Dosa (QAd) can be
expressed as
[
]
QAd = Wd .C pd . (Tdt − Tdd )
Δtd + [L. λv ]
Δtd
(10)
where Wd is average mass of Dosa batter, kg; Cpd heat capacity of Dosa
batter, kJ/kg o K; Tdd Dosa batter temperature, oC; Tdt temperature of the
Dosa top surface, oC: Δtd Dosa baking time, s; L moisture loss during
baking of Dosa, kg; and λv latent heat of water evaporation, kJ/kg.
The other factors such as heat of reaction, solution and heats of
vaporization of volatiles other than water are usually small and can be
ignored.
In order to test the exclusive effect of conductive heat transfer, Dosa were
heated from the bottom only (while preventing radiation by covering the
Dosa with an asbestos disc) on the hot plate of the oven at three different
preset temperatures. Thermal conductivity of Dosa was calculated by
setting the total heat absorbed by the Dosa equal to the expression for
conduction. The results of these experiments are given in Table 3.9 and
the average thermal conductivity was 0.42 W/m °C. The expressions for
radiation from hood surfaces given in equations are simplified by
assuming the value of both hood emissivity (εH) and the geometric factor
(fpr) to be unity, which are valid assumptions under the conditions of the
investigation. When Dosa was baked only through radiation heat, as
described earlier, there was no appreciable change on the product
111
surface (except for the formation of a thin hard layer). The characteristic
holes on the top of the Dosa were also absent. This could be attributed to
the fact of the Dosa not being in contact with the surface of the hot plate,
indicating the importance of conduction heating in baking of Dosa. The
result of test runs is given in Table 3.10. Using equation (10), the total
theoretical heat absorbed by the test Dosa was calculated using
temperature and moisture data given in Table 3.9. The value of specific
heat (Cp) is taken as 1.83 kJ / Kg.
°
K for computing the sensible heat
requirement of the Dosa. The emissivity of the Dosa surface (εp)
calculated by setting the total theoretical heat absorbed by the Dosa equal
to the expression for emissivity in equation (7), was found to be 0.31.
The complete heat transfer model as expressed by equation (9)
and (10) was then applied to the baking in the Dosa oven. The total heat
absorbed [equation (10)] was taken as a sum of latent heat and sensible
heat. On conducting several experiments each term of equation (9) was
calculated for this purpose. It can be noted that approximately 532.29 W
of the heat absorbed by the Dosa was latent heat of evaporation (Q3) of
water while sensible heat (Q2) was about 192.31 W. It is interesting to
note that, of the total heat transferred (QT) to the Dosa, about 98.51% was
transferred by conduction from the rotating hot plate and about 1.49%
was transferred by radiation from the hood (Table 3.11). The heat transfer
distribution clearly indicates the significant contribution from conduction,
which was crucial for the characteristic flavor and crustiness of the Dosa.
Thermal efficiency of the Dosa machine was found to be about 51.47%
(Table 3.5).
112
It would be of interest to obtain the temperature profiles across the
thickness of the Dosa. The time-temperature-distance relationship for the
body of uniform temperature subject to sudden source of heat can be
represented by the most general equation of this type (Kern, 1950).
Tp1 = C1 + C2 x + C3 e − pt e qx
(11)
Where, Tp1 is the temperature of the Dosa oC; C1, C2, C3, p and q are
constants. The initial and boundary conditions for the present case are,
x = x, t = 0, T0 = Tdd
x = 0, t = 0, T0 = C1 = Tp = Tdb
where, Tdd is temperature of Dosa batter at ambient conditions, o C; Tdb is
the Dosa bottom temperature, which is in equilibrium with the hot plate
temperature Tp, o C: t is the time, s: x thickness of Dosa, m.
Hence,
Tt = 0 = T0 = C1 + C2 x + C3 = Tdd
The above equation is valid only when C2 = 0, otherwise T0 would have to
vary with x, where as it is assumed to be uniform.
Hence
Tdd = C1 + C3 or C3 = Tdd − Tp
Substituting in equation (7) results in
(
Tp1 = Tdb + (Tdd − Tdb ) f1 x
(
Where, f1 x
2 αd t
)
2 αd t
)
(12)
denotes the error integral and α d the thermal
diffusivity, m2/s. The values of the integral are obtained from literature
(Kern, 1950.)
113
The study evolved standardized conditions for Dosa batter as well
as the optimum conditions for the large-scale preparations using the Dosa
making machine.
The formulation of the conventional batter having “rice and black
gram” in the ratio of 4: 1, fermented for 17 h at a temperature of 35~40°C
was found to be the ideal. Since the viscosity of the fermented batter was
high, it was essential to dilute the batter with water to make it to flow freely
and a ratio of 3: 1 of solid (“rice and black gram”) to liquid (water) was
found to be optimum for the machine. The study of microstructure of Dosa
using different hot plate materials indicated, the hot plate material having
high thermal conductivity namely the stainless steel or Teflon coated
aluminum would give product having good crispness and texture with
better Dosa flavour.
Instant batter powder prepared by drying the conventional batter
using tray drier had all the required attributes of the Dosa in terms of
colour, texture and crispness. The batter powder prepared by blending
different ingredients was also comparable to the conventional Dosa.
In baking of Dosas on the machine, conduction heat transfer was
found to play the most prominent role.
Hence, the amount of heat
supplied by individual modes of heat transfer may be controlled rather
than the total heat supplied to the product in order to obtain the desired
the Dosa quality. The mathematical expression could be of significant use
in estimating the magnitude of the heat transfer and contribution from
114
each individual heat transfer modes, which in turn is useful for design
modifications of the Dosa machine (burner and rotating hot plate). As a
result Dosas prepared by using stainless steel and Teflon coated
aluminum had better surface finish. The sensory analysis indicated a
good overall quality and acceptability of the Dosa baked on the machine.
The experimental temperature profiles across the thickness of the Dosa
indicates similar trend of the theoretical ones, however, the values of
temperature are lower than the theoretical ones which could be attributed
to the evaporative cooling that takes place during the baking of Dosa.
The sensory analysis indicates a reasonably good over all quality of the
Dosa baked on the Dosa machine.
The photograph of the improved Dosa machine is presented as
photograph-2. The automatic discharge mechanism of Dosa is discussed
in detail at Annexure 1.
115
Table 3.1: Wall and center temperature of the copper tube for Dosa
Batter
Time
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
52
54
56
58
60
Wall
Temperature
22
56
57
58
58
58
58
59
59
59
59
59
59
59
59
59
59
59
59
59
59
59
59
59
59
59
59
59
60
60
60
Center
Temperature
22
24
24
31
36
41
45
48
50
52
54
55
56
56
57
57
57
57
57
58
58
58
58
58
58
58
58
58
58
58
58
Table 3.2: Composition of Rice and Black gram
Sl
No.
Composition
Rice
%
Black gram
%
1
Carbohydrate
78.20
59.60
2
Protein N * 6.25
6.80
24.00
3
Fat
0.50
1.40
4
Ash
0.40
0.50
5
Moisture
13.70
10.90
Ref: Nutritive values of Indian Foods by C.Gopalan et.al, (Table – 1)
Table 3.3: Estimation of Thermal Properties of Instant Dosa Batter
Calorimeter
Batter
Mass
Mass
Drop in
Duration
Rise in
Trial
Wall Temp.
Temp.
of
of
bath
of
Temp. of
No
°C
°C
batter
water
temp.
heating
batter
* 10-3
in bath
°C
Min
°C
Thermal
Specific
Thermal
Diffusivity
Heat of
conductivity
* 10 –7
batter
of batter
m2 / s
kJ / kg ° C
W/ m °C
(Cpd)
(kdb)
(T1)
(T2)
kg
kg
(Δtd)
h
(T1-T2)
1
60
58
165
32.160
0.15
56
38
1.1674
3.2129
0.4159
2
60
58
160
31.420
0.15
56
38
1.1670
3.2370
0.4188
3
80
79
160
31.420
0.20
60
53
1.5197
3.0945
0.5214
4
80
79
160
31.060
0.20
60
55
1.6912
2.9479
0.5527
The Density of the instant Dosa batter (ρd) 1108.70 kg / m3
(αd)
Table 3.4: Comparison of Thermal Properties of Dosa Batter by Composition and Experimentation
Sl
Thermal property
No
Prediction by
By experimentation
composition
(Average)
1
Thermal Diffusivity * 10 –7 , m2 / s,
(αd)
1.2797
1.3863
2
Specific Heat of Batter, kJ / kg ° C,
(Cpd)
3.2316
3.1231
3
Thermal Conductivity of Batter, W/ m °C, (kdb)
0.4585
0.4772
4
Density of Batter, kg/m3,
-
1108.70
(ρd)
Table 3.5: Estimation of Thermal Efficiency of the Dosa Machine
Sensible Heat Q2d, kJ:
= 8,307.80
Latent Heat Q3d, kJ:
= 22,994.93
Total Heat QTd, kJ:
= 31,302.72
Calorific value of LPG Q1, kJ/Kg
= 60,814.90
Thermal efficiency of the Dosa machine (QTd/Q1)*100
= 51.47 %
Basis: 360 Nos. of Dosa produced by the machine per hour.
Table 3.6: Expansion Characteristic of Rice and Black gram during Soaking
Soaking time
h
Initial volume
Expanded volume
ml
ml
Rice
Black
gram
Expansion Index
Rice
Black
gram
Rice
Black
gram
110
110
-
-
-
-
1
-
-
165
240
1.45
2.18
2
-
-
170
260
1.55
2.36
3
-
-
170
270
1.55
2.45
4
-
-
170
270
1.55
2.45
5
-
-
170
270
1.55
2.45
Volume per 100 g of Raw Rice and Urdh dhal = 110 ml respectively.
Grinding time = 90 s
Table 3.7: Effect of Temperature on Quality of Fermented Dosa Batter
Sl
Fermentation
Fermentation
Initial volume of
Final volume of
No
Temperature
time
Batter
Batter
h
ml
ml
±5
o
C
1
25
17.00
100
100
2
30
17.00
100
110
3
35
17.00
100
130
4
40
17.00
100
220
5
40
17.00
100
230
Batter density = 1108.70 kg/m3
The ratio of Rice to Urdh dhal is 1: 0.25
Table 3.8: Effect of Ingredients* on Quality of Dosa using Conventional Batter
Sl
Quantity
Shear strength of Dosa
No
g
N
Rice
Black
Colour of Dosa
Batter Viscosity
m.Pa.s
With out oil
With oil
Top
Bottom
gram
1
500
0
5.77
5.24
20.92
25.35
195.85
2
500
75
6.90
6.69
29.27
30.08
625.60
3
500
125
8.52
6.33
21.60
26.44
1833.40
4
500
175
2.09
2.00
21.68
26.71
2041.40
* Rice, Black gram and salt (to taste)
Table 3.9: Average Thermal Conductivity (kd) as a Function of Hot Plate Temperature
Mass of
Hot
Dosa
Dosa
Mass
Total Heat
Heat
Temp.
Thermal
Trial
Batter
Plate
Dia.
Thick.
of Dosa
W
Capacity
of Dosa
Conductivity
No.
Kg
Temp.
* 10-3
* 10-3
Kg
(Flour)
C
m
m
(Final)
KJ/Kg oK
(Tp)
(Dd)
(xd)
(W1d)
(Initial)
(Wd)
o
(QTd)
Sensible
Latent
Heat
heat
(Q2d)
(Q3d)
o
C
Of Dosa
W/m. oC
(Cpdf)
(Td)
(kd)
1
0.100
185.00
207
2.10
0.07169
192.31
532.29
1.83
80.50
0.44
2
0.100
170.50
207
2.20
0.07600
188.84
451.33
1.83
74.60
0.43
3
0.100
172.00
208
2.00
0.07574
191.58
459.79
1.83
75.50
0.40
Table 3.10: Average Radiative Heat Transfer Coefficient (εpd) as a Function of Refractory Surface Temperature.
Mass of
Dosa
Dosa
Mass
Trial
Hood
Batter
Dia.
Thick.
Temp. of
of Dosa
Radiative
No.
Temp.
Kg
* 10-3
* 10-3
Dosa
Kg
Heat transfer
C
(Initial)
m
m
C
(Final)
Coefficient
(THd)
(Wd)
(Dd)
(xd)
(Td)
(W1d)
(εpd)
o
o
1
141.00
0.110
207.0
2.50
40.50
0.1030
0.29
2
160.30
0.100
205.0
1.90
50.20
0.0930
0.31
3
167.00
0.100
212.5
1.93
57.60
0.0920
0.33
Table 3.11: Complete Heat Balance of the Dosa Machine
S.No.
Description
Contribution
(W)
Percentage
%
1
Total heat absorbed by Dosa, QTd
724.60
100.00
2
Sensible heat absorbed by Dosa, Q2d
192.31
26.54
3
Latent heat absorbed by Dosa, Q3d
532.29
73.46
4
Heat absorbed by conduction, qcd
713.85
98.51
5
Heat absorbed by radiation, qRd
10.75
01.49
Basis: Heat transferred to a single Dosa
Water bath temperature
Stirrer
Product temperature (Tc)
Water Bath
Surface temperature of copper tube ( Ts)
Temperature controller
060.12
Water bath door
Heating Element
Thermocouple for product
Thermocouple for copper tube surface
Insulation of water bath
Batter
Stirrer blade
Teflon cap
Support plate
Water
Thermocouple for water bath
Fig. 3.1: Experimental Set-up for Measuring Thermal Diffusivity
70
60
50
40
Series1
Series2
30
20
10
0
1
3
5
7
9 11 13 15 17 19 21 23 25 27 29 31
Series 1: Wall temperature of the copper cylinder
Series2: Center temperature of the copper cylinder (Dosa Batter
temperature)
Fig. 3.2: Graph indicating the increase in Wall Temperature and
Center Temperature of the Copper Cylinder (Dosa batter)
128
Hood
Batter assembly
Oiling / Curry Dispenser
Circular Hot Plate
Spreader assembly
Scraper assembly
LPG Control valve
Circular burner
Vertical shaft
Panel board
Sproket
Main frame
Electric Geared Motor
Pump with solenoid valve
Ground
Cover
Pivot bearing
Fig. 3.3: Dosa Machine
Floating scraper assembly
Improved Batter dispenser
Improved Oil dispenser
Floating spreader assembly
Hood
Hot plate
Circular burner
LPG Control valve
Vertical shaft
Gear box
Panel board
Electric geared motor
Main frame
LPG cylinder
Castor wheel
Ground level
Fig. 3.4: Improved Dosa Machine
Hot Plate
Bush with Spring
Holding Bar
Chute
Radial Diverter
Radial Scraper
Fig. 3.5: Auto Discharge Assembly
Thumb wheel
Spreader bar -1
Compression spring
Spreader bar -2
Hot palte
Fig. 3.6: Floating Spreader Assembly
Holding bar
Compression spring
Vertical support
Main frame
Hot plate
Fig. 3.7: Floating Scraper Assembly
Batter container
Oil container
Batter valve
Solenoid
Teflon spreader
Hot plate
Fig. 3.8: Improved Batter/Oil Dispenser
Stainless Steel
Alloy Steel
Teflon Coated Aluminum
Cast Iron
Fig. 3.9: Microstructure of Dosa prepared on different hot plate materials
135
Profilogram of D osa made using D osa making machine
12
8
6
4
2
Attribute s
C
el
lu
la
r
Pu
ffi
ne
G
ss
ol
de
n
br
ow
n
Pa
st
y
C
ris
Te
pn
ar
es
in
s
g
St
re
ng
th
So
ur
Bi
tte
r
Sa
lti
ne
ss
St
al
e
0
O
Q
Mean scores
10
Fig. 3.10: Profilogram of Dosa made using Dosa machine
136
Dosa Machine
India has a large number of traditional foods which are relished by
people in different geographical locations in the country. Indian sweets
and snack food industry are on the threshold of revolution and identified to
have good export potential. Increased domestic demand is due to the
migration of people from villages to the urban centers. Further the
increased consumer demand for high quality and safe product at
affordable price has resulted in a need for mechanization as they are to
be produced in largescale. The mechanization of traditional foods is
gaining momentum in India, in which the food engineers and technologists
have a major role.
Indian traditional foods have a long history and the knowledge of
preparation of traditional foods has been passed on from generation to
generation. Efforts have been made to document this vast knowledge,
which is in the domain of a few families/individuals.
A large number of traditional convenience and confectionery food
products, both on household as well as commercial scale are prepared
from dehulled chickpea flour batter. Well-known food products prepared
from chickpea flour include sev (prepared by extrusion of dough followed
by deep fat frying) and (spherical shaped deep fat fried product made
from batter). Boondi is a popular product, consumed either as a fried
snack or as sweet boondi or bound together in the form of balls, called
boondi laddu (Bhat et al., 2001).
138
Many food operations are empirical, involving subjective judgment,
which cannot cope with unfamiliar eventualities and it has not yet become
possible to relate changes in such food processes or products to physical
conditions and properties which can be measured instrumentally. There is
a great need for understanding the physical properties of food products in
order that products and process can be amenable to the rapidly
increasing range of new technologies serving the food process industries
in general. It might be that a complete description of food products and
process conditions in purely physical terms will never be achieved, but
equally it is certain that better engineering property data will permit better
control of both process and product for the benefit of the producer,
processor and consumer.
Literature survey
traditional foods. With regard to the standardization of batters for different
Indian traditional foods, the work has been carried out by several people.
In order to form boondi globules, the batter is made to flow through
perforations in a tray of the boondi forming unit under mechanical
vibration. As the batter passes through the perforations, forming small
globules, fall directly into heating medium of the fryer (Ramesh et.al.,
2004). Preparation of boondi having a perfect spherical shape depends
on the water content of the batter, as the batter consistency (which
strongly depends on moisture content) plays a very critical role (Priya et
al., 1996). At low levels of water, boondi are oblong in shape. At higher
139
water levels also, the batter tends to spread in the frying medium again
leading to oblong shaped boondi with a tail like shape (Semwal et al.,
2005).
Many studies have been reported on the physico-chemical
characteristics of boondi. The deep fat frying characteristics of
bengalgram flour suspensions reported that boondi of a large size
absorbs less oil than smaller one (Bhat et al., 2001). Since the emphasis
in the preparation of legume based snack foods is on deep fat frying of
the batter, efforts have been made to reduce the oil content by
incorporating various additives. Priya and co-workers (1996) reported
studies on addition of carboxyl methyl cellulose (CMC) and hydroxymethyl
cellulose (HMC) as additives in reducing the oil content of fried boondi.
Storage studies of fried sweet boondi have been studied by Semwal et al
(2005). Especially the addition of sorbic acid and using different types of
packaging for increasing the shelf life of boondi. Storage studies of Khara
boondi in flexible films were also reported (Mahadeviah et al., 1979)
The mechanization and automation of boondi preparation offers a
challenge since many parameters affect the product quality. It is
necessary to understand the complex process that occurs during frying so
that improvements can be made by optimizing the process, leading to
better automation and optimization of the formulation (Singh et al., 1995
and Blumenthal et al., 1991). Amongst all, the moisture content of the
batter plays most important role. The oil content in the product, frying
time, shape of the globule are parameters dependent on the moisture
content of batter. From the consumer’s point of view, deep fat fried boondi
140
needs to be crisp, yellowish brown in colour and spherical in shape.
Although, the height of fall of Chickpea batter had some effect on the
shape, it is found insignificant in the operated range (Venkateshmurthy et
al., 2005).
the need for mechanization has been discussed by Ramesh (2004).
Understanding of the thermal properties of batter is another
important aspect in design of machinery for Indian traditional foods.
Design of the burner, estimation of heat load and evaluation of thermal
efficiency depend on the basic thermal properties of food materials.
Knowledge of thermal properties is essential for mathematical modeling
and computer simulation of heat and moisture transport (Rask, 1989;
Sablani et al., 1998). Since most foods are hygroscopic in nature, one
should consider how strongly they bind water, namely, moisture-solid
interaction during drying (Wang and Bernnam, 1992).
The main
parameter that significantly influences the thermal properties of the bulk of
food is the moisture content. This is because the thermal properties of
water were markedly different from those of other components (proteins,
fats, carbohydrates and air).
In situations where heat transfer occurs
under unsteady state condition, thermal diffusivity (α) is more relevant.
The value of ‘α’ determines how fast heat propagates through a material
and higher values indicate rapid heat diffusion. The ‘α’ of a material is
defined as the ratio of the heat capacity of the material to conduct heat
divided by its heat capacity to store it (McCabe; Smith & Harmot, 1995;
Charm, 1971; Heldman and Singh, 1993; Perry and Green, 1984). The
141
objection to steady state analysis is long time required to attain the steady
state conditions which in turn leading to changes in compositions during
measurement. There is also a possibility of moisture migration due to
maintaining the temperature difference across the material for a long
period of time (Urbicain and Lozano, 1997). Polley et al. (1980) have
compiled data on Cp of vegetables and fruits. Lamberg and Hallstrom,
(1986) have reported Cp over the temperature range of 20 to 90° C and a
moisture range of 8 to 85% (wet bulb) of freeze-dried Brintje potato. The
specific heat is often measured using method of mixing, adiabatic
calorimeter, differential scanning calorimeter (DSC) and differential
thermal analysis (DTA). DSC techniques have been vividly discussed by
Callanan and Sullivan (1986). The guarded hot plated method can also
be used for measurement of Cp.
Engineers have the great responsibility to connect science and
society, between pure knowledge and how it is used. There is a
responsibility that goes with that and need to think about implications, real
and imagined. We have to practice engineering to make things simple,
usable, secure and safe.
two principal areas of technical creative activity are closely interrelated.
The designer has to keep in mind the product designed by him/her to be
manufactured in the most economical way. Apart from the knowledge of
142
manufacturing aspects, he/she must be in touch with the consumer needs
to understand their requirement. The official regulations, national codes,
safety norms are to be given due consideration and these often play a
decisive part in determining the design.
Machine design can be broadly classified into three categories as
adaptive design, developmental design and new design. In adaptive
manufacture, or to use a new material.
In developmental design, a designer starts from an existing design
but the final result may differ quite markedly from the initial product. This
design calls for considerable scientific training and design ability.
New design, the one which never existed before, is done by only a
few dedicated designers who have personal qualities of high order. Lot of
research, experimental activity and creative ability is required for this.
Various steps involved in the design process could be summarized
as a) the aim of the design, b) preparation of the simple schematic
diagram, c) conceiving the shape of the unit/ machine to be designed, d)
preliminary strength calculation, e) consideration of factors like selection
of material and manufacturing method to produce most economical
143
design, f) mechanical design and preparation of detailed manufacturing
drawing of individual components and assembly drawing.
The selection of the most suitable materials for a particular part
becomes a tedious job for the designer partly because of the large
number of factors to be considered which have bearing on the problem
and partly because of the availability of very large number of materials
and alloys possessing most diverse properties from which the materials
has to be chosen. With the development of new material, a good
knowledge of heat treatment of materials which modifies the properties of
the material to make them most suitable for a particular application is also
very important. The material selected must possess the necessary
properties for the proposed application. The various requirements to be
satisfied can be weight, surface finish, rigidity, ability to withstand
environmental stress corrosion from chemicals, service life, reliability etc.
The four types of principal properties of material decisively affect their
selection, namely, physical, mechanical, chemical and ease of machining.
The thermal and physical properties concerned are co-efficient of
thermal expansion, thermal conductivity, specific heat, specific gravity and
electrical conductivity. The various mechanical properties are strength in
tensile, compressive, shear, bending, torsion and fatigue as well as
impact resistances. The properties concerned with the manufacture are
the weldability, castability, forgeability, deep drawing etc. The various
chemical properties concerned are resistance to acids, oxidation, water,
oils etc.
144
For longer service life, the parts are to be dimensioned liberally to
give reduced loading and due consideration given to its resistance to
thermal, environmental and chemical effects and to wear. Stainless steel
iron base alloy has a great resistance to corrosion. The property of
corrosion resistance is obtained by adding chromium or by adding
chromium and nickel together and stainless steel is manufactured in
electric furnaces. Selection of material for food processing machinery is
an added task for the designer. For most of the food application stainless
steel is the preferred material as the food material contains large amount
of moisture and product is for human consumption, hence needing
hygiene. In certain cases, where acid foods are handled, a special variety
of stainless steel having very low carbon content which has oxidationresistant property is recommended.
Justification
The main objective of the present study is to optimize the process
of mechanization of forming and frying of boondi. The mechanization and
automation of boondi preparation offers a challenge as many parameters
affect the product quality. It is necessary to understand the complex
process that occur during frying and improvements can be done by
optimizing the process leading to better automation and optimizing the
formulation.
The design of machinery for Indian traditional foods is new and a
specialized area. Very few organizations are involved in design and
development of such food processing machinery, which fall into the
145
category
of
new
design
and
involves
extensive
research
and
experimentation. Most of the foods processing machinery available in the
country are imported from other countries and most of them are for
processing of fruits, vegetables, bakery products, confectionery and oils.
A few industries have adapted these imported foods processing
machinery for Indian foods and potato chips is one among them.
For the large-scale production of fried boondi, as required by large
number of consumers, continuous boondi forming and frying machine has
been considered for design. As the value of time is increasing day by
day, the demand for the ready-to- eat traditional foods is also increasing.
Some traditional Indian foods such as sev boondi are more popular.
Though the basic kitchen technology for the production of these traditional
foods is known, considerable research and development efforts are
required to translate such technology to the large-scale production level.
This requires major inputs from food engineers and technologists. The
present study involves the standardization of forming of boondi,
standardization of Chickpea batter and heat transfer studies in frying of
boondi globules.
The machine design for Indian traditional foods is an exclusive
area for food/mechanical engineers and there are ample opportunities for
mechanization of these foods. The objective of the present work is to
design and develop machineries for Indian traditional foods incorporating
the different branches of engineering such as thermal, mechanical,
chemical,
electrical
and
electronic
and
food
engineering.
The
understanding of the physical, thermal and engineering properties of
146
foods is very important for the design of any food-processing machine.
Integration of the equipment developed with the technology of food
processing is also considered. In the present work the design and
development of traditional food machine such as Boondi making machine
with the standardization of respective food ingredients for Chickpea batter
is taken up.
Section 4.2.0: Materials and Methods
Oil
Commercially available vegetable oil (groundnut oil/sunflower oil) is
used for the frying of boondi and the quantity of oil used per batch is
around 30 liters.
Chickpea Flour
Chickpea flour was purchased from the market. Initial moisture
content of the flour was around 10%. The quantity of the chickpea flour
used is around 100 g /batch.
Preparation of Boondi
1000 g of chickpea flour having initial moisture of 10% was put into
a container and known quantity of water was added (in small quantities at
a time) and the mixture was stirred continuously to break the lumps and
form a homogenous batter. A domestic blender (250 W) was used for
147
uniform mixing of the batter. The
globules were made by a -forming
machine, as shown in Fig. 4.1. The product diameter was measured by a
digital vernier caliper (Mitutoyo, Japan) having a least count of 0.02 mm.
A hand held contactless infrared temperature (model- Center 350
series) indicator having range of 0 - 4000 C with a least count of 0.10o C
was used for recording the temperature of the frying oil and also the fried .
A stopwatch having a least count of 1 s was used to measure the time of
frying of the . By regulating the fryer rotational speed, the frying time was
maintained constant at 90 s which is essential for preparation at batch
scale level.
Determination of Compressive Strength
A universal texture-measuring instrument, (model no: LR5K, Lloyds
instruments, Fareham, UK) was used for the measurement of
compressive strength (an indicator of crispness) of the fried spheres of . A
crosshead speed of 50 mm/min was used to compress 50% of the
assigned height for obtaining the compressive strength (N) or crispness of
.
Estimation of Moisture Content of Batter
The moisture content of batter was estimated based on the amount
of water added during the preparation of Chickpea batter.
148
Determination of Colour
The colour of the was measured using a Labscan XE (C iIIuminant.
2° View angle). The L, a, b and the total colour difference (ΔE), which
represents the total colour of the sample were directly obtained from the
system.
Experimental Design
A central composite rotatable design (CCRD) with two variables
was used to study the response pattern and to determine the optimum
combination of the variables. To find a functional relationship of the total
colour difference and compressive strength, as a function of batter
moisture and hole diameter, a mathematical function Y = f (batter
moisture, hole diameter), was assumed. To approximate the function f, a
second-degree polynomial equation was used:
Y = bo + b1 x1 + b2 x 2 + b3 x 21 + b4 x1 x 2 + b5 x 21 + e
where bo is the intercept, b1, b2 to b5 are constants, co-efficient 'e' is the
response error and X's are coded independent variables. The actual value
and the corresponding coded value of independent variables used in
developing the experimental design are given in Table 4.1. The total
colour difference and the compressive strength were the two responses
measured. Optimization was carried out individually for the responses.
Analysis of variance, (ANOVA), a partial F test for the individual
parameters and analysis of residuals for total colour difference and
compressive strength were carried out.
149
Boondi was fried in the trough containing hot oil by discharging a
known amount of batter globules of
predetermined consistency
(Bhattacharya and Bhat, 1997). The probe of the temperature controller
was positioned through a hole at the center of bush to measure the
temperature of the hot oil (Venkateshmurthy et al., 2005).
Sensory Analysis
Sensory characteristics of the fried prepared on the forming/frying
machine were tested by 10 trained panelists from department of Sensory
Science using quantitative descriptive analysis.
Section 4.2.3 Measurement of Thermal properties,
Thermal diffusivity
Experimental Set-up
The experimental set-up is illustrated in Fig. 4.2. The set-up
consists of a copper tube of 2.25-inch diameter and a length of 9 inch.
Copper, being rigid and having high thermal conductivity value facilitates
high heat transfer coefficient, thus reducing the time taken to reach steady
state. The apparatus based on the transient heat transfer conditions
require only time- temperature data. The apparatus consists of an
agitated water bath in which the copper tube-containing Chickpea batter
was immersed. Thermocouples were soldered to the out side surface of
the cylinder monitoring the temperature of the sample at radius R. A thin
150
thermocouple probe indicated the temperature at the center of the
sample. The bottom end of the copper cylinder is fixed with a cap made of
Teflon (alpha=4.17*10-3 ft2/h) and filled with the Chickpea batter of known
weight. The cap made of Teflon material is used to close the top end of
the copper tube and the thermocouple is inserted to full immersion to
insure proper radial positioning. The cylinder is placed in the agitated
water bath and temperature of the wall and center temperature of the
copper cylinder (Chickpea batter temperature) are recorded until a
constant rate of temperature rise is obtained for both inner and outer
thermocouples (Table 4.2). A plot of wall temperature of copper cylinder
and the center temperature of Dosa batter temperature is as shown in the
graph at Fig. 4.3.
Under the condition of constant temperature rise, the Fourier’s
equation for the case when only radial temperature gradient exists.
Appropriate dimensions for the cylinder, Dickerson (1965) showed that
the maximum temperature difference (T1 – T2), or the establishment of
steady state takes place when,
αb θ
R 2 〉 0.55
(1)
Knowing the approximate range of ‘αb’ of the Chickpea batter and
considering a reasonable time ‘θ’ for collecting the time-temperature data,
appropriate radius of the cylinder ‘R’ was determined to be an inch. With
Teflon ends, as a good heat insulator, a length of 9 inches suitable for
water bath was considered (Dickerson, 1965).
151
The thermal diffusivity of the Chickpea batter can be evaluated by
using the equation
αb = A R2
4 (T1 − T2 )
(2)
where, where, αb, Thermal diffusivity of Chickpea batter, m2 / s; A,
The constant rate of temperature rise,
O
C/ min; R, Radius of the copper
cylinder, m; T1, The out side surface temperature of the copper cylinder,
O
C;
T2, Temperature of the batter inside the copper tube,
O
C; Θ,
Experimentation time, min.
Experimental Procedure
To evaluate the approximate vales of the thermal diffusivity and the
specific heat of the Chickpea batter, the mass fractions of the composition
of the Chickpea batter such as, carbohydrate, protein, fat, ash and the
moisture of the ingredients were noted from the literature. The main
ingredients of the Chickpea batter is Bengalgram or Chickpea. The
following are the composition of the Chickpea is given in Table 4.3.
The empirical predictive equations developed by Dickerson
(1969) and Sweat (1986) for the evaluation of the specific heat and
thermal conductivity respectively were used for the estimation. The
following are the predictive equations:
Specific Heat (Cpb)
C pb =1.42 mc + 1.549 m p + 1.675 m f + 0.837 ma + 4.187 mm
(3)
where, m is the mass fraction: while the subscripts are c,
carbohydrate; p, protein; f, fat; a, ash; and m, moisture.
152
Thermal Conductivity (kb)
kb = 0.25 mc + 0.155 m p + 0.16 m f + 0.135 ma + 0.58 mm
(4)
where, m is the mass fraction: while the subscripts are c,
carbohydrate; p, protein; f, fat; a, ash; and m, moisture.
Based on the above predictive values, the experimental duration is
fixed to be around 60 min. The known weight Chickpea batter was
transferred into the copper tube whose bottom end is closed by a Teflon
cap. The copper tube was closed on top by another Teflon cap and a
thermocouple was inserted to the full depth of the product (Chickpea
batter). An insulated water bath was used for the experimentation. The
water bath having a known quantity of water was maintained at a
predetermined temperature of 60°C and the temperature of the water was
controlled by a temperature controller having a least count of 0.01°C. The
time-temperature data of the surface of the copper cylinder and the core
temperature of the Chickpea batter were recorder at a time interval of 2
min.
Thermal diffusivity of Chickpea batter was estimated by substituting
appropriate values obtained during the experimentation in the equation
(2), considering R=1.125 inch. The average value of the thermal diffusivity
(Table 4.4) was found to be 1.37 m2/s. and Table 4.5 shows the predictive
and the experimental values of the thermal diffusivity.
Specific heat of Chickpea batter was evaluated by equating the
heat lost by the water bath (q1d) to that of the heat gained by the copper
tube (q2d). The drop in temperature of water in the bath was in the range
153
of 0.15 ~ 0.20 °C. The specific heat of the Chickpea batter was found to
be 2.87 kJ / kg OC, (Table 4.4) and the predictive and the experimental
values are shown in Table 4.5.
The average density of the Chickpea batter was found to be
1156.25 kg / m3. The thermal conductivity of the Chickpea batter was
estimated by substituting the values of the thermal diffusivity (αb), specific
heat (Cpb) and the density (ρb) of Chickpea batter in the equation; αb =
kb/ρb Cpb. The average value of the thermal conductivity of the Chickpea
batter is 0.45 W/m OC, (Table 4.4) and Table 4.5 shows the predictive and
the experimental values of the thermal conductivity.
1. Forming Machine
A continuous forming machine as shown as Fig. 4.1 is based on
the continuous forming of globules for traditional deep fat fried
products/sweet to different sizes and geometry hygienically by uniform
application of impact force. The device based on a vibrating perforated
forming sieve is used for the production of different regio-specific
traditional deep fat fried products/sweet. The device consists of a solenoid
which is coupled to the one end of the vertical rod through a pin and the
other end of the vertical rod is connected to the hinged forming sieve
through a split pin. One end of the forming sieve is hinged on to the main
frame through another hinge and the main frame slides inside a bush for
varying the height of fall of the formed batter. A timer is used for varying
154
the ON/OFF time of magnetization of the solenoid which gives impact to
the forming sieve.
2. Circular Deep Fat Fryer
Production of snack foods using a continuous circular deep fat fryer
is as shown in Fig. 4.4. Based on the concept of revolving trough and a
conveyorised discharge mechanism, the device to produce snack foods
has been designed. The device can be used for the purpose of frying of
different types of deep fat fried foods. The circular trough driven by a set
of sprocket and chain, which drives a gearbox and is mounted on the
main frame. The circular deep fat frying machine can be moved from
place to place by a set of rigid and swivel castors and the trough is
covered on top by a cover. A discharge mechanism as shown in Fig. 4.5
is provided for discharging of the deep fat fried product from the trough
assembly.
3. Improved Circular Deep Fat Fryer
An improved continuous circular deep fat fryer is as shown in Fig.
4.6. The device is based on the similar concept of the circular deep fat
fryer, but certain improvements have been incorporated based on the
initial experimentation of deep fat frying. It was observed that during frying
the food material lacked positive forward motion due to the relative motion
of oil and the trough. The circular trough having a set of spring loaded
flaps is driven by a set of sprocket and chain which drives a gear box and
is mounted on the main frame. The circular deep fat frying machine can
155
be moved from place to place by a set of rigid and swivel castors and the
trough is covered on top by a cover. The cover for the trough is perforated
to allow vapor to escape during the process of continuous deep fat frying
and the sides of the circular LPG burner is covered on all the sides by a
set of covers to avoid radiation of heat energy. A circular burner heats the
edible oil kept in the trough assembly and the temperature of the oil is
controlled by a digital temperature controller through a sensing probe
immersed in the oil bath inside the rotating trough. An improved discharge
mechanism as shown in Fig. 4.7 is provided for discharging of the deep
fat fried product from the trough assembly.
4. Energy Balance
The Chickpea batter has moisture content of 57% and the final
moisture in the fried product is around 3%. The heat source/burner for the
boondi frying machine is designed to supply heat during frying. The total
heat load on the frying machine involves the initial heat required to bring
the temperature of the oil to around 190 °C, the heat absorbed by the
metal trough and the total heat requirement for frying of the product. The
heat absorbed by the globules has two components, namely, the sensible
heat of water, the latent heat of evaporation of water. It was estimated
that the sensible heat of water is around 5423 kJ, the latent heat of water
to be 41,867 kJ. The total heat requirement of the frying machine is
around 55,750 kJ for frying of 34 kgs of Chickpea batter. The frying time
of the boondi is moisture dependent and the batter having moisture
content of 57% will take around 90 s for frying. From the large-scale trials
156
of the machine, the actual consumption of the fuel (LPG) was found to be
2.20 kg of LPG/h (1, 06,957 kJ) and the thermal efficiency of was found to
be about 49.93% (Table 4.6).
Commercially available LPG blend of butane and propane in the
ratio of 60:40. From the theoretical calculation the requirement of the
liquid petroleum gas for supplying the required heat to the hot trough is
estimated to be around 560 g, considering the calorific value of the LPG
as 48,651.92 kJ.
It was reported that 30 kgs of air is required for
complete combustion of the liquid petroleum gas. The loss of heat is to
the tune of 51,207.34 kJ and is accounted for the radiation loss in the
oven.
1. Boondi Forming Machine
Fig. 4.1 represents continuous forming machine for traditional
deep fat fried products into different sizes and geometry. The device is
useful for large-scale preparation/forming of globules of different batters.
The formed batter is allowed to drop in to the hot oil of the deep fat frying
machine. The consistency (water to flour ratio) of the batter is
standardized for the chickpea batter at 57% and the residence time for
frying of boondi to be about 90 s.
It consists of a solenoid, which is coupled to the one end of the
vertical rod through a pin and the other end of the vertical rod is
connected to the hinged forming sieve through a split pin. One end of the
157
forming sieve is hinged on to the main frame. The main frame slides
inside a bush for varying the height of fall of the formed batter and a timer
is used for varying the ON/OFF time of magnetization of the solenoid
which gives impact to the forming sieve against a stationer rod which is
welded to the main frame. The frequency of impact can be controlled by
varying the time period of the timer, a batter container with a control valve
is placed above the forming sieve. The batter container is mounted on the
main frame through a hole in the main frame, a toggle switch and the
timer are housed inside a panel board. The panel board is fastened to the
main frame. All the parts of the device are made of stainless steel.
2. Circular Deep Fat Fryer
The circular deep fat fryer is suitable for large-scale frying of
traditional foods.
Based on the concept of revolving trough and a
conveyorised discharge mechanism, a device to produce snack foods is
designed and developed for large-scale applications. The product
obtained is of uniform dimension, texture and frying is done continuously.
The device using this principle can be used for the preparation of different
types of deep fat fried foods.
The drawing as shown in Fig. 4.4 represents a circular deep fat
fryer. The device comprises of a geared motor and the speed of the
geared motor can be varied by using an AC drive mounted inside the
control panel to impart required circular motion to the trough assembly.
The circular trough is driven by a set of sprocket and chain, which drives a
gearbox mounted on the main frame. The device has the provision to be
158
moved from place to place by a set of rigid and swivel castors. The trough
is covered on top and the cover is perforated to allow vapor to escape
during the process of continuous deep fat frying. The sides of the circular
LPG burner is covered on all the sides by a set of covers to avoid
radiation of heat energy. A burner heats the edible oil kept in the trough
assembly and the temperature of the oil is controlled by a thermostat
through a sensing probe immersed in the oil bath inside the rotating
trough. The solenoid valve controls the supply of the LPG to the circular
burner to regulate the oil temperature and the ignition of the circular
burner is done by a pilot lamp mounted on the circular burner and is lit at
the time of starting of the circular deep fat fryer. A discharge mechanism
as shown in Fig. 4.5 is provided for discharging of the deep fat fried
product from the trough which comprises of a conveyor chain driven by a
set of rollers driven by a servo motor mounted on a set of side supports
and the deep fat fried products are guided on to the conveyor chain by a
diverter attached to the discharge mechanism. The movement of the oil
backwards is arrested by a dam placed inside the trough assembly and
discharge mechanism is mounted on the main frame using suitable
fasteners and all the electrical parts of the continuous deep fat fryer is
housed inside the control panel and is mounted on the main frame.
3. Improved Circular Deep Fat Frying Machine
During large-scale experimentation certain drawbacks of the device
were observed. During the circular motion of the trough it was observed
that the hot oil inside the trough moves in the opposite direction to that of
159
the trough. This reverse movement of the oil resulted in accumulation of
the formed globules and larger residence time for the fried product.
Hence, the product produced is of non-uniform in texture and colour
resulting in unsatisfactory end product. The discharge mechanism has a
conveyor, which is partly submerged inside the hot oil for picking of the
fried product. The rotation of the oil trough (oil) and the discharge
conveyor (for conveying the product) are in the same direction. As the
bottom of the conveyor approaches the fried product, oil is continuously
pushed backwards and the conveyor failed to pick the fried product from
the rotating trough. This was one of the serious draw back of the above
circular deep fat fryer.
In order to overcome the above drawbacks, an improved circular
deep fat fryer as shown in Fig. 4.6, was designed and developed. The
improved device is based on the concept of revolving trough having eight
sets of spring-loaded flaps and a reverse conveyorised discharge
mechanism.
The device consists of the following additional parts/components.
The circular trough has eight sets of spring loaded flaps to impart positive
motion to the product (Fig. 4.6). These flaps help in conveying the hot oil
and the food material imparting a set residence time. The flaps are spring
loaded and fold backwards when it comes in contact with the bottom plate
of the improved discharge mechanism as shown in Fig. 4.7. A reverse
discharge mechanism is provided for discharging of the deep fat fried
product from the trough assembly and the discharge mechanism
comprises of a conveyor chain driven by a set of rollers driven by a servo
160
motor mounted on a set of side supports and the deep fat fried products
are guided on to the conveyor chain by a diverter attached to the
discharge mechanism. The movement of the oil backwards is arrested by
a dam placed inside the trough assembly and discharge mechanism is
mounted on the main frame using suitable fasteners and all the electrical
parts of the continuous deep fat fryer is housed inside the control panel
and is mounted on the main frame.
Section 4.3.2: Standardization of Chickpea batter
1. Chickpea batter
Variables involved in the process of forming and frying are batter
moisture, die hole diameter, height of fall, frying time, frying temperature
and product diameter. It was observed that two variable, namely, the
moisture content of the batter and die hole diameter significantly
influenced the colour and texture (compressive strength) of the fried
product. The two responses, that is, the total colour difference and the
compressive strength were measured for under different combinations of
batter moisture content and hole diameter of the forming unit. The
diameter of the globules was measured at different locations on the
surface and the range of ten readings (randomly picked globules) is
provided in Table 4.7. During the experimental runs, oil temperature was
maintained at 185±3 °C and the height of fall of the batter was fixed at 80
mm above the oil surface. Table 4.1 and 4.8 provides the details of coded
and uncoded variables and corresponding responses. The two responses
were analyzed using ANOVA and the data are presented in Table 4.9 and
161
4.10. The lack of fit, which measures the failure of the model to represent
the data in the experimental domain at points that are not included in the
regression, was insignificant at p < 0.01.
2. Total Colour Change
The response surface for the total colour change was generated
using a second order polynomial as shown in Fig. 4.8 Higher value (0.90)
of coefficient of determination indicated the goodness of fit. The colour
development was minimum for with higher diameter (above 4 mm) and at
low moisture levels (0.524 -0.545 g/g of batter). The presence of higher
amount of moisture at increased diameter made the soggy and uncooked
at the end of 90 s, which resulted in lower colour development. The
globules with smaller diameter have relatively lower moisture and fried
quickly to develop colour. However, at higher moisture levels, the colour
values did not vary significantly with diameter, although values were lower
with smaller diameter .
Increase in moisture did not change the colour values at lower
diameter (< 3.5 mm), It was observed that at this diameter the formed
had good sphericity (Table 4.10) and spherical shaped globules rotated
on their axis during frying resulting in rapid frying, which is reflected by the
quicker colour development.
3. Compressive Strength
The force required to compress 50% of the globule was taken as
the compressive strength. The compressive strength is an indicator of the
162
crispness of the product or degree of frying with lower values indicating
the highly crispy nature of the product. Fig. 4.9 shows the response
surface for compressive strength at different combinations of moisture
content and diameter of . Lower values of compression (< 7 N) obtained
at lower diameters (< 3.5mm) and moisture levels (0.524-0.535 g/g of
batter) indicating that the crispy nature of . With increase in diameter the
values increased at lower moisture (< 0.545 g/g of batter), which may be
attributed to the moisture content and effect of shape of . The maximum
values for globules (sphericity) were seen with lower die diameter and
high moisture content. The tendency of the globule to elongate at higher
moisture at these diameters observed during experimentation may be
responsible for the above. However when diameter was increased the
values dropped at higher moistures indicating better frying. No significant
change was observed when the moisture content was increased above
4.5 mm. It could be seen that the moisture content in the globule plays a
major role in deciding the degree of frying. In combination with the
diameter of the forming unit, moisture content also determines the shape
of the product for the given height of fall of globule.
4. Optimization and Frying Conditions
The 3D graphs (Fig. 4.8 and Fig. 4.9) were converted into contour
plots and were superimposed (Fig. 4.10) to obtain optimum conditions. It
can be seen from the figure that diameter of 3 - 3.25 mm at 0.524 -0.535
g/g gave desired results. Fairly good results were obtained at 3.25 – 3.50
diameter of 4.75 – 5.00 mm and 0.556 to 0.565-g/g moisture. Another
163
parameter, which is the shape of globules, was taken into consideration.
This indicated that lower diameter globules are more spherical in shape;
compared to higher diameter (Table 4.10). Keeping this in view the
optimum range selected is 3.0 - 3.5 mm of die hole diameter and moisture
content of batter in the range 0.525 - 0.540 g/g. The fried under these
conditions had values of total colour change and compression in the
range of 49-50 and 3-7 N respectively. The fried in the above conditions
had good appearance (visual observation) and crispy mouth feel.
To check the validity of the model, the experiments were carried
out at optimum values of moisture 52 and 54 % and die hole diameter 3.0
& 3.5 mm respectively as given in Table 4.10. The predicted values of
compression and total colour change were estimated using the equation
developed for the two responses. The higher R2 values (0.88 and 0.91)
for compression and total colour showed the goodness of the fit of the
model.
Section 4.3.3: Heat transfer analysis
Theoretical Aspects
Submerged/or deep fat frying is an important unit operation in food
industry. Submerged frying is a simultaneous heat and mass transfer
process. When the heat is transferred to the food material from the oil
bath, water evaporates from food material and oil is absorbed by it. It is
essential
to
understand
heat
transfer
that
takes
place
during
Submerged/deep fat frying of Indian traditional foods such as . The
164
variations of the physical properties of the food materials add to the
complexity of the understanding of the frying process (Hallstrom, 1988).
The heat transfer takes place in boondi in two phases, 1)
Conductive heat transfer under unsteady state conditions with in the
Boondi globule, 2) Convective heat transfer between the Boondi globule
and the surrounding groundnut oil. The study of heat and mass transfer is
complicated owing to the vigorous movement of the Boondi globules
inside the oil creating turbulence during moisture escape. The water
vapour moving from the lower half of the prevent efficient heat transfer.
The moisture evaporation decreases with time due to reduced moisture in
the globule.
It is reported that the deep fat frying operation (Farakas, 1994) is
composed of four distinct stages, 1) Initial heating, 2) Surface boiling, 3)
Falling rate and 4) Bubbling end point.
Initial heating: In this stage of heating the food material (the moisture
and food) attains the boiling temperature of water through natural
convection and this last for few seconds.
Surface boiling: Once the food attains the boiling temperature of water
the evaporation of the surface moisture begins at this stage. The mode of
heat transfer changes from natural convection to forced convection
because of the turbulence and a crust (dry region) will be formed on the
surface of the food.
Falling rate: This stage of frying process evaporation of more moisture
from the food material and the core temperature of the product rises to the
boiling point of water. This stage is similar to the falling rate period
165
observed in food dehydration. The crust layer increases in thickness and
evaporation of moisture reduces.
Bubble end point: When the food material is fried for longer period of
time the moisture removal reduces and no more bubbles seen escaping
from the surface of the food material and this stage is referred as the
bubble end point. During this stage of the frying process, the crust
thickness increases. During the study of the thermal properties of the
Chickpea batter, thermal conductivity of the Chickpea batter was
measured experimentally and found to be 0.44 W/m OC.
During the heat transfer analysis, the following are the assumptions
made,
It is assumed that the heat transfer is one-dimensional. Phase
change in the core is due to conduction. Food is homogeneous and
isothermal. Heat required for the chemical changes is negligible. Heating
medium is under constant temperature.
The crust surface temperature of the globule is given by
K b (T3 − T4 )
r = ho (T5 − T3 )
(5)
where, Kb thermal conductivity of the Chickpea batter, W/m OC: T3
surface temperature of the
globule,
O
C: r radius of the
globule,
O
C: T4 core temperature of the
globule, m: ho surface heat transfer co-
efficient of groundnut oil, W/m2 OC: T5 temperature of groundnut oil, OC
and
h0 = K b (T3 − T4 )
r (T5 − T3 )
(6)
The details of the formulae are discussed by Vijayan and Singh
(1997). By substituting the relevant terms in the equation (6), the average
166
convective heat transfer co-efficient of the groundnut oil was estimated to
be 236.58 W/m2 OC (Table 4.12).
A continuous circular deep fat fryer was developed and machine
design was optimized based on the understanding of the engineering and
thermal properties of the chickpea flour batter and results of forming as
well as frying studies. The product quality parameters such as colour
(total colour change), crispness (compressive strength) and product
shape (sphericity) were considered for the optimization. The formed with
frying time of 90 s, temperature 185± 3 °C, height of fall of batter 80 mm,
batter having 0.524-0.545 g/g of moisture and diameter 3.0 – 3.5 mm
were crispy with acceptable colour and overall quality.
In submerged frying of , the mode of heat transfer is convective
heat transfer from the hot oil to the globule and conduction from the
surface to the core of the globule. The average surface heat transfer coefficient of the groundnut oil to be 236.58 W/m2 OC. The results of the
thermal properties, such as thermal diffusivity, specific heat, thermal
conductivity and heat transfer studies of Chickpea batter were useful for
design modifications of the burner and the rotating circular trough of the
deep fat fryer. The circular trough material having high thermal
conductivity will lead to uniform distribution of heat to groundnut oil (frying
medium). Based on frying time-temperature of , a speed variator and a
temperature controller is incorporated to vary the frying time (rotational
167
speed) and to control the temperature of the hot groundnut oil for different
diameters of the globule respectively.
Thermal efficiency of the submerged frying machine is found to be
about 49.93%.
The complete design of the forming and frying machine and the
standardization of the Chickpea batter involved iterative development of
the machine and the Chickpea batter. Many times the machine was
modified to suit the machine and on few occations the batter was modified
to suit the deep fat frying machine. This iterative process continued till the
repetitive results for largescale preparation of fried was obtained.
The photograph of the improved machine is presented as
photograph-3. A simple heat balance for estimation of fryer capacity is
given in Annexure 2.
168
Table 4.1: Coded and Uncoded Process Variables and their Levels
Studied for
Variables
Moisture in
batter,
g/g
Die Diameter,
mm
+2
+1
0
-1
-2
0.524
0.535
0.545
0.556
0.565
5.0
4.5
4.0
3.5
3.0
Table 4.2: Wall and Center Temperature of the Copper Tube
For Chickpea batter
Time
Wall
Temperature
Center
Temperature
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
22
56
58
58
59
59
59
59
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
20
21
24
30
36
41
45
48
50
52
54
55
55
56
57
57
57
58
58
58
58
58
58
58
58
58
Table 4.3: Composition of Chickpea
Sl
Composition
No.
Chickpea
%
1
Carbohydrate
59.80
2
Protein N * 6.25
20.80
3
Fat
5.60
4
Ash
0.40
5
Moisture
9.90
Ref: Nutritive values of Indian Foods by C.Gopalan et.al, (Table - 1)
Table 4.4: Estimation of Thermal Properties of Chickpea Batter
Trial Calorimeter
No
wall temp.
°C
Batter
temp.
°C
Mass
of
batter
* 10-3
kg
Mass
of
water
in bath
kg
Drop
in bath
temp.
°C
Duration
of
heating
Min
Rise in Thermal
temp. diffusivity
of
* 10 –7
m2 / s
batter
°C
(αb)
(T1-T2)
38
1.3075
Specific
heat of
batter
kJ / kg
°C
(Cpb)
2.8781
Thermal
conductivity
of batter
W/ m °C
1
(T1)
60
(T2)
58
185
31.850
0.15
50
2
60
58
180
31.650
0.15
50
38
1.3075
2.9168
0.4410
3
65
63
180
32.160
0.20
50
42
1.4452
2.7591
0.4610
4
65
63
185
32.250
0.20
50
41
1.4140
2.9430
0.4812
The Density of Chickpea batter (ρb) 1156.25 kg/m3
(kb)
0.4351
Table 4.5: Comparison of Thermal Properties of Chickpea Batter by Experimentation and
Composition
Sl
No
1
Thermal property
Thermal Diffusivity of batter * 10 –7, m2 / s, (αb)
By experimentation
(Average)
1.3075
Prediction by
composition
1.3235
2
Specific Heat of batter, kJ / kg °C,
(Cpb)
2.8975
2.7942
3
Thermal conductivity of batter, W/ m °C,
(kb)
0.4381
0.4276
(ρb),
1156.25
-
4
Density of Batter, kg/m
3
Table 4.6: Complete Heat Balance on the Deep Fat Frying of
S.No.
Description
Contribution
Percentage
W
%
1
Total heat absorbed by , QTb
658133.73
100.00
2
Sensible heat absorbed by , Q2b
122420.77
18.60
3
Latent heat absorbed by , Q3b
535712.96
81.40
4
Calorific value of LPG Q1, kJ/Kg
5
Thermal efficiency of the machine
106957.40
(QTb/Q1)*100
49.93 %
Basis: Heat transferred to 34 Kgs of Chickpea batter per hour, having 57% of added water
Table 4.7: Sphericity of Boondi Globules
Sl No
Moisture in batter
Forming unit die
diameter,
1
g/g
0.534
mm
3
5/5
5/6
4/5
2
0.545
3
5/5
5/4
5/6
3
0.534
4
6/6
6/5
7/6
4
0.545
4
7/8
7/7
8/6
5
6
0.534
5
6/6
6/8
7/8
0.545
5
7/6
7/8
8/8
Sphericity of ,
mm*
* Diameter measured at different places on the surface of the boondi globule.
Table 4.8: Central Composite Rotatable Design and Response Functions
Variables
Design
points
1
2
3
4
5
6
7
8
9
10
11
12
13
Response variables
Coded
Coded
Uncoded
Uncoded
X2
Moisture in
batter
g/g
Diameter
X1
-1
-1
1
1
0
0
-2
2
0
0
0
0
0
-1
1
-1
1
-2
2
0
0
0
0
0
0
0
0.534
0.534
0.555
0.56
0.545
0.545
0.523
0.565
0.545
0.545
0.545
0.545
0.545
3.5
4.5
3.5
4.5
3.0
5.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
Colour
Compression, N
Experimental
Predicted
Experimental
Predicted
48.96
46.85
50.26
49.18
49.70
47.78
49.25
51.07
49.45
49.88
50.14
50.25
49.67
49.79
47.84
50.39
49.87
49.57
47.10
40.44
51.07
49.90
49.90
49.90
49.90
49.90
8.13
10.98
11.76
9.15
8.05
7.84
9.74
11.56
9.20
8.58
7.80
9.20
8.65
7.50
10.20
11.14
8.38
8.32
8.26
10.09
11.91
8.97
8.97
8.97
8.97
8.97
mm
Table 4.9: Analysis of Variance (ANOVA) for Fitted Second Order Polynomial Model and Lack of
fit for Total Colour Difference and Compressive Strength as per CCRD
DOF
SS
MS
Total colour difference
Regression
5
11.33
2.26
Residual
7
3.24
0.46
Pure error
4
0.67
0.16
Lack of fit
3
2.57
0.85
Total
12
14.58
Compressive Strength, N
Regression
5
18.27
3.65
Residual
7
4.19
0.59
Pure error
4
1.66
0.41
Lack of fit
3
2.53
0.84
Total
12
22.46
DOF: Degree of Freedom
F
Significance
of
F
4.88
0.03
2.11
6.10
0.01
2.03
Table 4.10: Experimental and Predicted Values of Compression at Optimized Frying Conditions.
Sl
Moisture
Forming
Sphericity
No
in batter
unit die
of
Colour
Compression
diameter
g/g
mm
mm*
N
Experimental
Predicted
Experimental
Predicted
1
0.524
3.0
5/5
6/5
6/5
5.2
3.8
49.95
49.76
2
0.524
3.5
7/6
7/5
8/6
9.3
7.1
49.90
49.52
3
0.545
3.0
5/4
5/4
5/5
8.7
8.3
49.91
49.61
4
0.545
3.5
8/7
8/7
7/6
9.6
8.8
50.06
49.92
R square = 0.88
R square = 0.91
Table 4.11: Estimated Co-efficient for Fitted Polynomial Representing Relationship Between
Response and Process Variables
Co-efficient
Compressive
strength
Total colour
difference
b0
N
102.23
18.26
b1
-0.82
-2.60
b2
-3.95
70.85
b3
0.00
0.02
b4
0.10
-0.54
b5
-1.19
-0.67
Table 4.12: Average Convective Heat Transfer Co-efficient (ho) as a Function of Hot Oil
Temperature of Globules
Boondi
Globule
radius
* 10-3 m
Surface
temperature
of
Boondi
o
C
Core temperature
of Boondi
C
W/m2. oC
(T5)
(r)
(T3)
(T4)
(ho)
1
180
3.00
130
87
251.18
2
180
3.00
130
92
221.97
3
180
3.00
132
90
245.34
Average
Trial
Oil
No. temperatur
e
o
C
o
Convective Heat
transfer co-efficient
Solenoid valve
Batter container
Timer
Batter control valve
Hinge
Rotating Trough
Forming sieve
Switch
Vertical connecting rod
Deep Fat Frying Machine
Stationery rod
Hot Oil Bath
Main frame
Main frame hinge
Fig. 4.1: Boondi Forming Machine
Water bath temperature
Stirrer
Product temperature (Tc)
Water Bath
Surface temperature of copper tube ( Ts)
Temperature controller
060.12
Water bath door
Thermocouple for product
Heating Element
Thermocouple for copper tube surface
Batter
Teflon cap
Insulation of water bath
Stirrer blade
Support plate
Water
Thermocouple for water bath
Fig. 4.2: Experimental Set-up for Measuring Thermal Diffusivity
70
60
50
40
Series1
Series2
30
20
10
25
23
21
19
17
15
13
11
9
7
5
3
1
0
Series 1: Wall temperature of the copper cylinder
Series2: Center temperature of the copper cylinder (Chickpea Batter
temperature)
Fig. 4.3: Graph indicating the increase in Wall Temperature and
Center Temperature of the Copper Cylinder Chickpea batter
183
Perforated Hood/cover
Discgarge Mechanism
Circular Oil Trough
LPG BUrner
Heat Shield
Reduction Gear Box
Panel Board
Main Frame
Ground Level
Castor Wheel
Fig. 4.4: Circular Deep Fat Frier
Rollers
Side supports
Hot Oil Trough
Fried Boondi Gloubles
Geared Motor
Conveyor Chain
Direction of Conveyor
Fig. 4.5: Discharge Mechanism
Circular Oil Trough ( 8 segments)
Spring Loaded Flap
Reverse Discharge Mechanism
Spring Loaded Flap
Perforated Hood/cover
Product
Reverse Discgarge Mechanism
Circular Oil Trough
LPG BUrner
Heat Shield
Trough View
Electric Motor
Reduction Gear Box
Panel Board
Main Frame
Ground Level
Castor Wheel
Fig. 4.6: Improved Circular Deep Fat Frier
Geared Motor
Conveyor Flaps
Hot Oil Trough
Direction of Oil Motion
Conveyor Base Plate
Boondi Gloubles
Rollers
Fig. 4.7: Improved Discharge Mechanism
Chute
54
53
Total color change
52
51
0.57
0.56
0.56
0.55 Moisture
0.55 content (g/g)
0.54
0.53
0.53
0.52
50
49
48
47
46
45
3
3.5
4
4.5
Diameter, mm
5
Fig. 4.8: 3D graph showing the influence of die plate diameter on
moisture content in batter and colour change in Boondi
188
Compression, N
17
15
13
0.57
11
0.56
9
0.55
7
0.53
5
3
0.52
3.00 3.50 4.00 4.50
Moisture
content (g/g)
5.00
Diameter, mm
Fig. 4.9: 3D graph showing the influence of die plate diameter on moisture
content in batter and Texture (crispness) of
189
Fig. 4.10 Contour plots showing the influence of die hole diameter and total
colour change on processing parameters of (------ Die
diameter,
Moisture in batter)
190
Photograph 3
Boondi machine
5.1.0 Conclusion and suggestion for future work
Traditional foods are gaining importance due to their nutritive
values in addition to the taste. To meet the increased demand it is
required to produce them hygienically at large scale, which in turn require
machinery or equipments. In the present thesis a few equipment for the
production of traditional foods are discussed in detail in terms of their
design and development vis-à-vis standardization of the batter/dough to
suit the machine and vice versa. The importance of heat transfer analysis
in identifying the desired mode of heat transfer, rather than total amount
of heat transfer, in order to optimize a given design of equipment is
highlighted. The thermal and physical properties of batter/dough which
are required to do the thermal analysis but not easily available in the
literature have been measured/estimated.
This exercise of design and development of equipment for the
large scale hygienic production of traditional foods received considerable
encouragement for environmental reasons as well. This is because the
present thesis demonstrates the possibility of replacing the conventional
heat sources such as diesel, electricity with Liquefied Petroleum Gas
(LPG). This results in two-fold benefit: One in terms of savings in energy
(at least by 20%) and the other in terms of eco friendliness of the fuel (the
combustion products of LPG are CO2 & water and non toxic).
As a category, Indian traditional food industry is the largest, both in
terms of tonnage and value. However, the production is done at different
levels, mostly in unrecognized sector, barring a few large industries. In
order to improve the quality and shelf life of these products, the important
192
need of the hour is automation of this traditional food industry irrespective
of the scale. In addition to quality, for the conservation of material and
energy, timely knowledge at physical, chemical, microbial and sensory
attributes through offline, online, and in the monitoring are essential. The
measurement of many of these attributes, which are not possible till
recent past, is now possible due to rapid advancements in instrumentation
and process control.
Application sophisticated technologies such as
neural networks, fuzzy logic etc in process control is to be enhanced.
Computer based control and monitoring of the process with the help of
online sensors and analyzers is to be taken up as a challenge in the
present food processing industry.
With this is in view, design and development of some of the
equipment is suggested below
1. Continuous sterilization equipment with PLC controls in
view of the current batch type steam retorts.
2. Simple equipment for the sterilization of spices without the
use of steam.
3. High pressure puffing equipment/Gun puffing device.
193
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Annexure 1
Discharging Mechanism of Dosa:
There are three operations involved in the discharging of the Dosa,
namely, the scraping, rolling and discharging (radial motion) into the
collection chute.
Baked Dosa is scraped, rolled and discharged automatically by a
stationery scraper (either straight edge or curvilinear) fixed on to the rotating
hot plate. Continuous scraping (rolling) and discharging (radial movement
away from hot plate) are to be synchronized such that the product doesn’t
role one inside the other.
The resultant force of centrifugal force and gravitational force on the baked
Dosa plays an important role in
the radial movement (radial movement
away from hot plate). Hot plate is rotates at a speed of 0.5 RPM and the
corresponding centrifugal force C f on Dosa during scraping and rolling is
given by
C f = (W
g) ω2 R
(1)
Where, W , is the weight of Dosa; ω , angular velocity of hot plate; and R ,
the mean radius of the hot plate.
It may be noted that, since the centrifugal force C f is much smaller than
weight of the Dosa W , it couldn’t be discharged away from the hot plate.
203
The scraper is inclined to the radius of the hot plate at certain angle θ (to the
axis of the plate)
Considering the motion of the hot plate, radial force generated by the circular
motion of the hot plate is given by
{ (
F = W V2
2 −
V1
2
)
(r2 − r1 ) }Cos θ
(2)
where F , is the force; W , weight of Dosa, V1 and V2 , are the linier velocities
of the hot plate at radius r1 and r2 respectively; and Cos θ component of the
force acting away from the hot plate due to the inclination of the scraper.
The following condition is essential for the radial discharge of the
Dosa, namely,
F + Cf 〉 W
(3)
From the calculations, for the values of θ , V1 , V2 , W , r1 , r2 the above
condition is found to hold the circular motion of the hot plate and successful
scraping and rolling was observed during the large scale trails of the Dosa
machine.
204
Example
Considering typical values of considering typical values of W = 75 g; V1 , V2 =
1.05 and 1.02 m/min respectively; r1 , r2 = 0.333 and 0.325m respectively, θ
= 15°, N = 0.5 RPM , R = 0.6 m and substituting in equations (1) and (2)
We get
F = 562 g and C f = 0.32 g (force)
Total force = 562.32 g
From equation (3), we have,
F + Cf 〉 W
562.32 g 〉 75 g
From the above it can be seen that the radial force is much higher than the
weight of the Dosa. It can be concluded that the circular motion of the hot
plate generate a radial force of 562 g to move the food material away from
the hot plate center.
205
Annexure 2
Heat balance for estimation of capacity of fryer
Fryer manufacturers determine the capacity of the fryer by the
experience of the equipment user. In deep fat frying, oil to product ratio is
very important and would differ from product to product based on the initial
moisture content.
The predictive model is based on the heat load on the fryer with out
considering the heat loss in the fryer.
We have total heat contained in the fryer by the frying medium is given by
Q = mo . C p . Δ T
(1)
where, Q is the total heat contained in the frying medium; mo . , mass of the
frying oil; C p specific heat of oil; Δ T , temperature gradient of the oil.
Taking the typical values of specific heat of groundnut oil and temperature
raise from room temperature to the frying temperature,
We have
Q = 368.28 mo
(2)
The heat is transferred from the heat source such as LPG burner to the wall
of the fryer and in turn the heat transferred to the oil. During deep frying, the
heat contained in the oil is transferred to the product by convection. The heat
transferred to the product has three components, namely, the sensible heat
206
of water, sensible heat of solid and latent heat of evaporation of water and
can be written as
Q = m. C p . Δt (water ) + m. C p . Δ t ( solids ) + m. λ ( Latent heat )
(3)
Considering values of specific heat C p of water, food material and
temperature rise of water and solids from room temperature to boiling point,
and the latent heat of evaporation of water, we get
Q = m f (1332.3 + 37.63 C p ).
(4)
where, m f is the mass of solid (flour) and C p specific heat of solid.
It is known that the heat dissipated by the frying medium is the heat
absorbed by the product and equating (2) and (4), we get
m0 = m p (3.62 + 0.075 C p )
where, m0 is the mass of the frying oil and m p the mass of the product.
Example
Considering typical values of a fryer,
We have m0 = 60 kg, C p = 3.275 (Chickpea flour),
m p = {(60.00
(2.652 + 0.075 * 3.275 ))}
= 20.71 kg.
It can be noted that the 60 kg of oil is essential for frying of 20.71 kg of
Chickpea globules.
207

- Central Food Technological Research Institute

Transcription

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