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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
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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

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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

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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

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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).

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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

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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

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Chapter 3: Chapter 3: Dosa Machine Dosa Machine 3.1.0 3.1.0 Introduction Introduction 3.2.0 3.2.0 Materials and Methods Materials and Methods 3.2.13.2.1 Materials Materials 3.2.23.2.2 Methods Methods 3.2.33.2.3 Measurement of Thermal Properties Measurement of Thermal Properties 3.2.4 3.2.4 Design of Machine Design of Machine 3.3.0 3.3.0 Results and Discussion Results and Discussion 3.3.13.3.1 Design and Development Design and Development 3.3.2 3.3.2 Standardization of Dosa Batter Standardization of Dosa Batter 3.3.3 3.3.3 Heat Transfer Analysis Heat Transfer Analysis 3.4.0 3.4.0 Conclusions Conclusions

Chapter 4: Boondi Machine

4.1.0 Introduction

4.2.0 Materials and Methods

4.2.1 Materials

4.2.2 Methods

4.2.3 Measurement of Thermal Properties

4.2.4 Design of Machine

4.3.0 Results and Discussion

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

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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

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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

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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

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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

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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

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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)

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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 )

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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

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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

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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

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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

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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

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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

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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

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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 sub-

assembly 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

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viii

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.

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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

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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 waste-

disposal 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.

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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

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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, shallow-

fried 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.

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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

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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

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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

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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.

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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

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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

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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

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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

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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

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14

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.

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Schematic of Machine Development

Thermo physical properties Processing

Thermal properties

Technology of Food

Food processing machinery

Food machinery

Physical properties Conceptual schematic

Standardization of Ingredients Thermal Diffusivity

Thermal conductivity

Specific heat Standardization of preparatory

operations

Energy / Heat requirement

FOOD PROCESSING MACHINE

Fabrication

Engineering Design

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1.1: Versatile Grating Machine

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Fig. 1.2: Hot Air Popping Machine

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Fig. 1.3: Bio – Plate Forming Machine

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Fig. 1.4: Integrated Hot Air Roasting Machine

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Fig. 1.5: Continuous Lemon Cutting Machine

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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

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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

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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

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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.

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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

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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

combination of theory, modern knowledge of materials, awareness of the

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

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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

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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.

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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.

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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

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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).

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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.

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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.

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Improved Pneumatic Extruder

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.

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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 (N-

200) 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,

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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,

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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 sub-

assemblies 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 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

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

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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 cross-

sectional 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 non-

uniform sheet of dough.

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Improved Pneumatic Extruder

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

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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

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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.

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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

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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

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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-

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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 whole-

wheat 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.

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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

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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

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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

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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

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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

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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).

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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

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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

( ) cctcbccCc xTTAkq −= .. (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

( )ctRccFcFc TTAhq −= .. (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.

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Radiation

( )ctHccprcRc TTAFq 44... −= σ (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

( ) ( ) ( ){ }11.1111 −+−+= Hcrccpcprcprc AAfF εε (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

RcFcCcTc qqqQ ++= (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):

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CcTc qQ =

( ) cctcbcc xTTAk −= .. (5)

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

( )[ ] [ ] cvccdctpccAc tLtTTCWQ Δ+Δ−= λ... (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

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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.

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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 Chapathi-

machine. The design of the machine involved iterative process of

incorporation of minor changes in the machine as well as the dough

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58

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.

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Table 2.1: Chemical and Rheological Characteristics of Flour Samples.

Quality characteristics Whole wheat

flour Atta

Chemical

Moisture, % 8.40 11.30

Ash, % 1.24 0.64

Dry gluten, % 10.80 10.40

Damaged starch 15.10 7.32

Farinograph

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

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Table 2.2: Effect of Water and Optional Ingredients* on the Rheological Characteristics of Chapathi Dough.

Rheological Characteristics

Whole Wheat Flour Atta

Water, % Salt Fat Salt + Fat

Water, % Salt Fat Salt + Fat

63 65 67 56 58 60 Research Water Absorption meter (RAWM)

Extrusion time, sec 200 120 75 105 65 72 150 110 70 90 45 45 Farinograph Peak consistency, BU 850 730 710 675 700 640 760 700 650 640 665 610 Dough development time, min

1.0 0.5 0.5 1.5 0.5 1.5 1.0 1.0 1.0 1.5 1.0 1.5

Stability, min 1.0 0.5 1.0 2.5 1.0 2.0 2.0 1.5 1.5 5.0 1.0 3.5 Mixing tolerance index, BU

240 170 200 135 160 110 210 190 200 70 180 110

Extensograph Resistance to extension, BU

480 400 360 520 360 440 510 470 400 580 360 370

Extensibility, * 10-3 m 60 60 62 72 76 84 82 87 88 95 100 106 Area, cm2 36 29 28 52 33 45 53 53 45 76 45 57 Penetrometer Compliance, % 37.5 41.1 46.9 40.0 46.5 47.1 35.6 40.1 44.0 37.7 49.4 50.6 Elastic recovery X 10,mm 6.95 7.05 7.10 8.70 6.90 8.51 9.45 9.48 9.72 11.83 8.27 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

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Table 2.3: Effect of Slit Width on the Thickness of Chapathi Sheet.

Slit width, * 10-3 m

Chapathi sheet thickness * 10-3

Whole wheat flour

m Atta 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

df 76 SEM ± 0.0134 0.0149

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

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Table 2.4: Effect of Water and Optional Ingredients* on the Sheeting Characteristics of Chapathi Dough.

Characteristics Whole Wheat Flour (WWF) Atta (A)

Water, % Salt Fat Salt

+ Fat

Water, % Salt Fat Salt +

Fat

63 65 67 56 58 60

Extrusion pressure,

kg/cm2

3.5 3.0 2.5 5.0 2.5 4.0 4.5 4.0 3.5 4.5 3.0 3.5

Chapathi sheet

thickness, * 10-3 m

1.34 a

1.4

7 b

1.5

8c

1.55c 1.3

0 a

1.40 d

1.6

6A

1.59 B

1.50 C

1.66 A

1.43 D

1.53 C

df 114 SEM ±0.01438 df 114 SEM ±0.01438

Chapathi sheet

weight, g

25.8 a

27.

7b

29.

2c

29.9c 27.

0 b

27.8 b

34.

8A

33.6 B

32.0 C

36.9 D

28.3 E

33.0 B

df 114 SEM ±0.21 df 114 SEM ±0.26

Un-used dough, % 40 38 40 41 38 42 38 41 42 40 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.

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Table 2.5: Effect of Water and Optional Ingredients* on the Quality of Chapathi.

Rheological characteristics

Whole Wheat Flour Atta

Water, % Salt Fat Salt + Fat Water, % Salt Fat Salt

+ Fat

63 65 67 56 58 60

Puffed height, mm 60 65 70 61 52 49 70 80 86 75 57 52

df

30

SEM ±0.06 df

30

SEM ±0.05

Pliability, mm 21 24 26 20 29 23 24 25 27 22 31 28

df

30

SEM ±0.03 df

30

SEM ±0.04

Baking loss, % 26.8 28.9 32.3 19.0 25.9 23.7 20.9 19.3 20.2 20.9 23.3 23.6

Appearance DBN

U

LBU DGNU LBU DBNU LBU LBU DONU LBU DBNU LBU

* 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;

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Table 2.6: Comparative Quality Characteristics of Chapathi made by Manual and Mechanical Sheeting.

Quality characteristics Whole wheat

flour Atta

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

Texture S S S S

* NS: Not significant at 5 % level (P<0.05)

LBU – Light brown uniform; S – Soft; SH – Slightly hard

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Table 2.7: Average Thermal Conductivity (kc) as a Function of Hot Plate Temperature of Whole Wheat Flour.

Trial No.

Hot

plate Temp.

oC (Tp)

Chapathi

Dia. m

* 10-3 (Dc)

Chapathi

Thick. m

* 10-3 (xc)

Total Heat

W

(QTc)

Thermal Conductivity

of Chapathi

W/m. oC (kc)

Dough Mass

kg (Initial)

(W1)

Mass of Chapathi

kg (Final)

(Wc)

Temp. of Chapathi

oC

(Tc)

Heat Capacity

(Wheat Flour) kJ/kg oK

(Cpc)

Sensible Heat (Q2c)

Latent heat (Q3c)

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

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Table 2.8: Average Thermal Conductivity (kc) as a Function of Hot Plate Temperature of Atta.

Trial No.

Hot

plate Temp.

oC (Tp)

Chapathi

Dia. m

* 10-3 (Dc)

Chapathi

Thick. m

* 10-3 (xc)

Total Heat

W

(QTc)

Thermal

Conductivity W/m. oC

(kc)

Dough Mass

kg (Initial)

(W1)

Mass of Chapathi

kg (Final)

(Wc)

Temp. of Chapathi

oC

(Tc)

Heat

Capacity (Wheat Flour)

kJ/kg oK (Cpc)

Sensible Heat (Q2c)

Latent heat (Q3c)

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

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Table 2.9: Complete Heat Balance on the Chapathi Baking Oven.

S.No. Description Contribution Percentage (W) %

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

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68

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

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Photograph 1A

Chapathi sheeting unit

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Photograph 1B

Chapathi machine

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Fig. 2.1: Chapathi Machine

Elevation

Motor

Gear Box

Hot Plate - 2

Diverter - 2

Diverter - 1

Gas Burner

Sheeting Unit

LPG Cylinder

Hot Plate - 1

Drawing Not to ScaleDrawing Not to Scale

Hot Plate - 1

LPG Cylinder

Sheeting Unit

Gas Burner

Diverter - 1

Diverter - 2

Hot Plate - 2

Gear Box

Motor

Elevation

Figure - 1: Chapathi Making Machine

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Return Conveyor Dusting Sub-Assemly

Improved Pneumatic extruder

Diverter / ChutesCircular Moving cutter

Main Drive

Fig. 2.2: Chapathi Sheeting Unit

Cutter Roller

Drawing Not to ScaleDrawing Not to Scale

Cutter Roller

Figure - 2: Chapathi Sheeting Device

Main Drive

Circular Moving cutterDiverter / Chutes

Improved Pneumatic extruder

Dusting Sub-AssemlyReturn Conveyor

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Quick Fix Coupling

Bolt / Nut

Gas Deflector

Gasket

Gasket

Bottom Cover PlateBottom Flange

Plates (For varying the thickness of sheet)

Top Flange

Top Cover Plate

WHEAT DOUGH

Conical Vessel

Note: Working Pressure of the cylinder 6 ksc

Fig. 2.3: Pneumatic Extruder

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Cylindrical Vessel

AIR INLET

Note: Working Pressure of the cylinder 6 ksc

Extruded sheet, 1.5 mm thick

ELEVATIONStrips / Bottom slit plate

Fig. 2.4: Improved Pneumatic Extruder

END VIEW

Slit 1.5 * 180 mm

Top Flanges/ Cover Plate

Sliding Piston

Dough

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Dusting Sub-Assembly - 2

Roller Chain

Sprockets / Antifriction Bearings

Chain Conveyor

Frame

Dusting Sub-Assemly - 1

Geared Motor

Slat Cutter Assembly

Return Conveyor

Cutting Roller

Drawing Not to Scale

Fig. 2.5: Dusting and Cutting Device

Tube / Rotary Brush / Sieve

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Sheeting Unit

Hot Plate - 1

Gas Burner

Diverter - 1

Diverter - 2

Hot Plate - 2

Gear Box

Motor

Elevation

End View

Plan

Outlet chute

Transfer chute

Chapathies

Inlet chute of sheeting unitOutlet chute

Drawing Not to Scale

Fig. 2.6: Chapthi Baking Unit

Oiling device

Oiling device

Figure - 3: Chapthi Baking Unit

Drawing Not to Scale

Outlet chuteInlet chute of sheeting unit

Chapathies

Transfer chute

Outlet chute

Plan

End View

Elevation

Motor

Gear Box

Hot Plate - 2

Diverter - 2

Diverter - 1

Gas Burner

Hot Plate - 1

Sheeting Unit

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Section 3.1.0: Introduction

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

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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

A review of the status of machinery for Indian traditional foods and

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

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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 soy-

Dosai 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

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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

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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 cereal-

based 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 cereal-

based 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

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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).

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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).

There are very few reports of development of machinery for Indian

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,)

Design of Traditional Food 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 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

design the designer is concerned with the adaptation of the existing

design. Such design does not demand special knowledge or skill and the

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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

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

combination of theory, modern knowledge of materials, awareness of the

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

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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

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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.

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Section 3.2.0: Materials and methods

Section 3.2.1: Materials

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.

Section 3.2.2: Methods

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

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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.

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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

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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.

Measurement of Temperature

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.

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Determination of Thermal Conductivity

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

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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.

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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

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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,

55.02 ⟩Rd θα (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

( )212 4 TTRAd −=α (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

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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)

mafpcpd mmmmmC 187.4837.0675.1549.142.1 ++++= (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)

mafpcdb mmmmmk 58.0135.016.0155.025.0 ++++= (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

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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

OC, (Table 3.3). The predictive and the experimental values of the thermal

conductivity are given in Table 3.4.

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Section 3.2.4: Design of Machine

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

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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

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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.

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Section 3.3.0: Results and Discussion

Section 3.3.1: Design and Development

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 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 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

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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:

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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

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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

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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

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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).

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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

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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

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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

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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

( ) ddtdbddCd xTTAkq −= .. (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

( )dtRddFdFd TTAhq −= .. (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.

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Radiation

( )dtHddprdRd TTAFq 44... += σ (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

( ) ( ) ( ){ }111111 −+−+= Hdrddpdprdprd AAfF εε (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

RdFdCdTd qqqQ ++= (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):

RdCdTd qqQ +=

( ) ( )dtHddprdddtdbdd TTAFxTTAk 44.... −+−= σ (9)

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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

( )[ ] [ ] dvddddtpddAd tLtTTCWQ Δ+Δ−= λ... (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

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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

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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).

qxptp eeCxCCT −++= 3211 (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,

ddTTtxx === 0,0,

dbp TTCTtx ===== 10,0,0

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,

ddt TCxCCTT =++=== 32100

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

pdddd TTCorCCT −=+= 331

Substituting in equation (7) results in

( ) ( )txfTTTT ddbdddbp α211 −+= (12)

Where, ( )txf dα21 denotes the error integral and dα the thermal

diffusivity, m2/s. The values of the integral are obtained from literature

(Kern, 1950.)

113

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Section 3.4.0: Conclusions

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

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115

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.

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Table 3.1: Wall and center temperature of the copper tube for Dosa

Batter Time Wall

TemperatureCenter

Temperature 0 22 22 2 56 24 4 57 24 6 58 31 8 58 36 10 58 41 12 58 45 14 59 48 16 59 50 18 59 52 20 59 54 22 59 55 24 59 56 26 59 56 28 59 57 30 59 57 32 59 57 34 59 57 36 59 57 38 59 58 40 59 58 42 59 58 44 59 58 46 59 58 48 59 58 50 59 58 52 59 58 54 59 58 56 60 58 58 60 58 60 60 58

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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)

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Table 3.3: Estimation of Thermal Properties of Instant Dosa Batter

The Density of the instant Dosa batter (ρd) 1108.70 kg / m3

Trial No

CalorimeterWall Temp.

° C

(T1)

Batter Temp.

° C

(T2)

Mass of

batter * 10-3

kg

Mass of

water in bath

kg

Drop in bath

temp. ° C

(Δtd)

Duration of

heating Min h

Rise in Temp. of

batter ° C

(T1-T2)

Thermal

Diffusivity * 10 –7

m2 / s (αd)

Specific Heat of batter

kJ / kg ° C (Cpd)

Thermal conductivity

of batter W/ m °C

(kdb)

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

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Table 3.4: Comparison of Thermal Properties of Dosa Batter by Composition and Experimentation

Sl No

Thermal property Prediction by composition

By experimentation (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, (ρd) - 1108.70

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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.

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Table 3.6: Expansion Characteristic of Rice and Black gram during Soaking

Initial volume ml

Expanded volume ml

Expansion Index

Soaking time h

Rice Black gram

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

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Table 3.7: Effect of Temperature on Quality of Fermented Dosa Batter

Sl No

Fermentation Temperature

± 5 oC

Fermentation time

h

Initial volume of Batter

ml

Final volume of Batter

ml

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

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Table 3.8: Effect of Ingredients* on Quality of Dosa using Conventional Batter

Sl No

Quantity g

Shear strength of Dosa N

Colour of Dosa Batter Viscosity m.Pa.s

Rice Black gram

With out oil With oil Top Bottom

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)

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Table 3.9: Average Thermal Conductivity (kd) as a Function of Hot Plate Temperature

Trial No.

Mass of Batter

Kg (Initial)

(Wd)

Hot Plate Temp.

oC (Tp)

Dosa Dia. * 10-3

m (Dd)

Dosa

Thick. * 10-3

m (xd)

Mass of Dosa

Kg (Final) (W1d)

Total Heat W

(QTd)

Heat Capacity(Flour)

KJ/Kg oK (Cpdf)

Temp. of Dosa

oC

(Td)

Thermal Conductivity

Of Dosa W/m. oC

(kd)

SensibleHeat (Q2d)

Latent heat (Q3d)

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

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Table 3.10: Average Radiative Heat Transfer Coefficient (εpd) as a Function of Refractory Surface Temperature.

Trial No.

Hood Temp.

oC (THd)

Mass of Batter

Kg (Initial)

(Wd)

Dosa Dia. * 10-3

m (Dd)

Dosa

Thick. * 10-3

m (xd)

Temp. of

Dosa oC

(Td)

Mass of Dosa

Kg (Final) (W1d)

Radiative

Heat transfer Coefficient

(εpd)

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

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(W) %

Table 3.11: Complete Heat Balance of the Dosa Machine

S.No. Description Contribution 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

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Stirrer

Water Bath

Heating Element

Insulation of water bath

Water

Water bath temperature

Product temperature (Tc)

Surface temperature of copper tube ( Ts)

Water bath door

Thermocouple for water bath

Thermocouple for product

Thermocouple for copper tube surface

Stirrer blade

Support plateTeflon cap

Temperature controller

060.12

Fig. 3.1: Experimental Set-up for Measuring Thermal Diffusivity

Batter

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0

10

20

30

40

50

60

70

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

Series1Series2

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

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Pivot bearingCover

Fig. 3.3: Dosa Machine

Drawing Not to Scale

Ground

Pump with solenoid valve

Oiling / Curry Dispenser

Vertical shaft

Scraper assembly

Panel board

Main frame

Electric Geared Motor

Sproket

LPG Control valveCircular burner

Spreader assembly

Hood Batter assembly

Circular Hot Plate

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Fig. 3.4: Improved Dosa Machine

Ground level

Castor wheel

Drawing Not to Scale

LPG cylinder Main frame

Panel boardElectric geared motor

Gear box

Circular burner

LPG Control valve Vertical shaft

Hood

Hot plate

Improved Oil dispenser Floating spreader assembly

Improved Batter dispenser

Floating scraper assembly

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Chute

Radial Diverter

Radial Scraper

Holding Bar

Bush with Spring

Hot Plate

Fig. 3.5: Auto Discharge Assembly

Drawing Not to Scale

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Fig. 3.6: Floating Spreader Assembly

Drawing Not to Scale

Hot palte

Compression spring

Spreader bar -2

Drawing Not to Scale

Spreader bar -1

Thumb wheel

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Compression spring

Fig. 3.7: Floating Scraper Assembly

Hot plate

Drawing Not to Scale

Main frame

Vertical support

Holding bar

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Fig. 3.8: Improved Batter/Oil Dispenser

Hot plate

Batter container

Solenoid

Oil container

Batter valve

Teflon spreader

Drawing Not to Scale

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Stainless Steel Teflon Coated Aluminum

Alloy Steel Cast Iron

Fig. 3.9: Microstructure of Dosa prepared on different hot plate materials

135

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136

Profilogram of Dosa made using Dosa making machine

0

2

4

6

8

10

12

OQStal

e

Saltine

ssBitte

rSou

rPas

ty

Crispn

ess

Tearin

g Stre

ngth

Cellula

r

Puffine

ss

Golden

brow

n

Attribute s

Mea

n sc

ores

Fig. 3.10: Profilogram of Dosa made using Dosa machine

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Dosa Machine

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Section 4.1.0: Introduction

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

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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

There are very few reports of development of machinery for Indian

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

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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

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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).

A review of the status of machinery for Indian traditional foods and

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

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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.

Design of Traditional Food Machinery

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.

Designing process requires an organized synthesis of known

factors and the application of creative thinking. Design and production, the

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

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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

design the designer is concerned with the adaptation of the existing

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 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

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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.

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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 oxidation-

resistant 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

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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

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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

Section 4.2.1: Materials

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.

Section 4.2.2: Methods

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

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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.

Measurement of Temperature

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.

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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:

exbxxbxbxbxbbY o ++++++= 12

521412

32211

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.

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Determination of Thermal Conductivity

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

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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,

55.02 ⟩Rb θα (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).

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The thermal diffusivity of the Chickpea batter can be evaluated by

using the equation

( )212 4 TTRAb −=α (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,

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 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)

mafpcpb mmmmmC 187.4837.0675.1549.142.1 ++++= (3)

where, m is the mass fraction: while the subscripts are c,

carbohydrate; p, protein; f, fat; a, ash; and m, moisture.

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Thermal Conductivity (kb)

mafpcb mmmmmk 58.0135.016.0155.025.0 ++++= (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

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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.

Section 4.2.4: Design of Machine

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

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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

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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

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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.

Section 4.3.0: Results and Discussion

Section 4.3.1: Design and Development

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

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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

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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

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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

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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

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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

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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

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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

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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

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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

( ) ( )3543 TThrTTK ob −=− (5)

where, Kb thermal conductivity of the Chickpea batter, W/m OC: T3

surface temperature of the globule, OC: T4 core temperature of the

globule, OC: r radius of the globule, m: ho surface heat transfer co-

efficient of groundnut oil, W/m2 OC: T5 temperature of groundnut oil, OC

and

( ) ( )35430 TTrTTKh b −−= (6)

The details of the formulae are discussed by Vijayan and Singh

(1997). By substituting the relevant terms in the equation (6), the average

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convective heat transfer co-efficient of the groundnut oil was estimated to

be 236.58 W/m2 OC (Table 4.12).

Section 4.4.0: Conclusions

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 co-

efficient 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

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168

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.

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Table 4.1: Coded and Uncoded Process Variables and their Levels

Studied for

Variables +2 +1 0 -1 -2

Moisture in batter,

g/g

0.524 0.535 0.545 0.556

0.565

Die Diameter,

mm 5.0 4.5 4.0 3.5

3.0

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Table 4.2: Wall and Center Temperature of the Copper Tube For Chickpea batter

Time Wall

Temperature Center

Temperature 0 22 20 2 56 21 4 58 24 6 58 30 8 59 36 10 59 41 12 59 45 14 59 48 16 60 50 18 60 52 20 60 54 22 60 55 24 60 55 26 60 56 28 60 57 30 60 57 32 60 57 34 60 58 36 60 58 38 60 58 40 60 58 42 60 58 44 60 58 46 60 58 48 60 58 50 60 58

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Table 4.3: Composition of Chickpea

Sl No.

Composition 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)

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Table 4.4: Estimation of Thermal Properties of Chickpea Batter

Trial No

Calorimeter wall temp.

° C

(T1)

Batter temp.

° C

(T2)

Mass of

batter * 10-3

kg

Mass of

water in bath

kg

Drop in bath temp.

° C

Duration of

heating

Min

Rise in temp.

of batter

° C (T1-T2)

Thermal diffusivity

* 10 –7

m2 / s

(αb)

Specific heat of batter kJ / kg

°C (Cpb)

Thermal conductivity

of batter W/ m °C

(kb)

1 60 58 185 31.850 0.15 50 38 1.3075 2.8781 0.4351

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

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Table 4.5: Comparison of Thermal Properties of Chickpea Batter by Experimentation and Composition

Sl No

Thermal property By experimentation (Average)

Prediction by composition

1 Thermal Diffusivity of batter * 10 –7, m2 / s, (αb) 1.3075 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

4 Density of Batter, kg/m3 (ρb), 1156.25 -

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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 106957.40

5 Thermal efficiency of the machine (QTb/Q1)*100 49.93 %

Basis: Heat transferred to 34 Kgs of Chickpea batter per hour, having 57% of added water

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Table 4.7: Sphericity of Boondi Globules

Sl No Moisture in batter

g/g

Forming unit die diameter,

mm

Sphericity of ,

mm*

1 0.534 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 0.534 5 6/6 6/8 7/8

6 0.545 5 7/6 7/8 8/8

* Diameter measured at different places on the surface of the boondi globule.

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Table 4.8: Central Composite Rotatable Design and Response Functions

Variables Response variables

Coded Coded Uncoded Uncoded Colour Compression, N

Design points

X1

X2

Moisture in batter

g/g

Diameter

mm

Experimental Predicted Experimental Predicted

1 -1 -1 0.534 3.5 48.96 49.79 8.13 7.50 2 -1 1 0.534 4.5 46.85 47.84 10.98 10.20 3 1 -1 0.555 3.5 50.26 50.39 11.76 11.14 4 1 1 0.56 4.5 49.18 49.87 9.15 8.38 5 0 -2 0.545 3.0 49.70 49.57 8.05 8.32 6 0 2 0.545 5.0 47.78 47.10 7.84 8.26 7 -2 0 0.523 4.0 49.25 40.44 9.74 10.09 8 2 0 0.565 4.0 51.07 51.07 11.56 11.91 9 0 0 0.545 4.0 49.45 49.90 9.20 8.97 10 0 0 0.545 4.0 49.88 49.90 8.58 8.97 11 0 0 0.545 4.0 50.14 49.90 7.80 8.97 12 0 0 0.545 4.0 50.25 49.90 9.20 8.97 13 0 0 0.545 4.0 49.67 49.90 8.65 8.97

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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 F Significance of F

Total colour difference Regression 5 11.33 2.26 4.88

Residual 7 3.24 0.46 0.03

Pure error 4 0.67 0.16 2.11

Lack of fit 3 2.57 0.85

Total 12 14.58

Compressive Strength, N Regression 5 18.27 3.65 6.10

Residual 7 4.19 0.59 0.01

Pure error 4 1.66 0.41 2.03

Lack of fit 3 2.53 0.84

Total 12 22.46

DOF: Degree of Freedom

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Table 4.10: Experimental and Predicted Values of Compression at Optimized Frying Conditions.

Sl No

Moisture in batter

g/g

Forming unit die

diameter mm

Sphericity of

mm*

Colour Compression

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

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Table 4.11: Estimated Co-efficient for Fitted Polynomial Representing Relationship Between Response and Process Variables

Co-efficient

Compressive

strength

N

Total colour difference

b0 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

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Trial No.

Average Oil

temperature

oC

(T5)

Boondi Globule radius * 10-3 m

(r)

Surface temperature

of Boondi

oC

(T3)

Core temperature of Boondi

oC

(T4)

Convective Heat transfer co-efficient

W/m2. oC

(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

Table 4.12: Average Convective Heat Transfer Co-efficient (ho) as a Function of Hot Oil Temperature of Globules

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Main frame hinge

Main frame

Hinge

Batter control valve

Batter container

Timer

Switch

Fig. 4.1: Boondi Forming Machine

Drawing Not to Scale

Deep Fat Frying Machine

Hot Oil Bath

Rotating Trough

Solenoid valve

Vertical connecting rod

Stationery rod

Forming sieve

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Stirrer

Water Bath

Heating Element

Insulation of water bath

Water

Thermocouple for water bath

Stirrer bladeSupport plate

Temperature controller060.12

Fig. 4.2: Experimental Set-up for Measuring Thermal Diffusivity

Batter

Teflon cap

Thermocouple for copper tube surface

Thermocouple for productWater bath door

Surface temperature of copper tube ( Ts)

Product temperature (Tc)

Water bath temperature

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0

10

20

30

40

50

60

701 3 5 7 9 11 13 15 17 19 21 23 25

Series1Series2

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

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Fig. 4.4: Circular Deep Fat FrierDrawing Not to Scale

Perforated Hood/cover

Discgarge Mechanism

Circular Oil Trough

LPG BUrner

Heat Shield

Reduction Gear Box

Panel Board

Main Frame

Castor Wheel

Ground Level

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Fig. 4.5: Discharge Mechanism

Direction of Conveyor

Hot Oil Trough

Conveyor Chain

Geared Motor

Side supports

Rollers

Drawing Not to Scale

Fried Boondi Gloubles

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Fig. 4.6: Improved Circular Deep Fat Frier

Ground Level

Drawing Not to Scale

Reduction Gear Box

Castor Wheel

Main Frame

Panel Board

Perforated Hood/cover

Circular Oil Trough

Reverse Discgarge Mechanism

Heat Shield

LPG BUrner

Spring Loaded Flap

Spring Loaded Flap

Circular Oil Trough ( 8 segments)

Reverse Discharge Mechanism

Product

Trough ViewElectric Motor

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Drawing Not to Scale

Hot Oil Trough

Fig. 4.7: Improved Discharge Mechanism

Direction of Conveyor Chute

Direction of ConveyorDirection of Conveyor

Direction of Oil Motion

Boondi Gloubles

Rollers

Conveyor Base Plate

Conveyor Flaps

Geared Motor

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45

46

47

48

49

50

51

52

53

54

Tota

l col

or c

hang

e

3 3.5 4 4.5 50.52

0.530.53

0.540.55

0.550.56

0.560.57

Diameter, mm

Moisture content (g/g)

Fig. 4.8: 3D graph showing the influence of die plate diameter on

moisture content in batter and colour change in Boondi

188

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3579

11131517

Com

pres

sion

, N

3.00 3.50 4.00 4.50 5.000.52

0.53

0.55

0.56

0.57

Diameter, mm

Moisture content (g/g)

Fig. 4.9: 3D graph showing the influence of die plate diameter on moisture

content in batter and Texture (crispness) of

189

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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

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Photograph 3

Boondi machine

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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

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193

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.

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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 on Dosa during scraping and rolling is

given by

fC

( ) RgWC f2ω= (1)

Where, , is the weight of Dosa; W ω , angular velocity of hot plate; and R ,

the mean radius of the hot plate.

It may be noted that, since the centrifugal force is much smaller than

weight of the Dosa W , it couldn’t be discharged away from the hot plate.

fC

203

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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

( ) ( ){ } θCosrrVVWF 122

12

2 −= − (2)

where , is the force; W , weight of Dosa, , are the linier velocities

of the hot plate at radius respectively; and

F 21 VandV

2rand1r θCos 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,

(3) WCF f ⟩+

From the calculations, for the values of 2121 ,,,,, rrWVVθ 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

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Example

Considering typical values of considering typical values of W = 75 g; =

1.05 and 1.02 m/min respectively; = 0.333 and 0.325m respectively,

21,VV

21, rr θ

= 15°, , and substituting in equations (1) and (2) RPMN 5.0= mR 6.0=

We get

F = 562 g and = 0.32 g (force) fC

Total force = 562.32 g

From equation (3), we have,

WCF f ⟩+

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

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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

Tpo CmQ Δ= .. (1)

where, is the total heat contained in the frying medium; , mass of the

frying oil; specific heat of oil;

Q

C

.om

p TΔ , 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

omQ 28.368= (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

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of water, sensible heat of solid and latent heat of evaporation of water and

can be written as

( ) )(.)(.... heatLatentmsolidsCmwatertCmQ tpp λ+Δ+Δ= (3)

Considering values of specific heat 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

pC

( ).63.373.1332 pf CmQ += (4)

where, is the mass of solid (flour) and specific heat of solid. fm pC

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

( )pp Cmm 075.062.30 +=

where, is the mass of the frying oil and the mass of the product. 0m pm

Example

Considering typical values of a fryer,

We have = 60 kg, = 3.275 (Chickpea flour), 0m pC

pm = ( )( ){ }275.3*075.0652.200.60 +

= 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


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