Postharvest Technology and Food Process Engineering

567 Pages·2014·23.34 MB·English

by  Amalendu Chakraverty, R. Paul Singh

Postharvest
Technology
and Food Process
Engineering

Amalendu Chakraverty
R. Paul Singh

Postharvest
Technology
andFood Process
Engineering

CRC Press is an imprint of the
Taylor & Francis Group, an informa business

Boca Raton London New York

Postharvest
Technology
andFood Process
Engineering

Amalendu Chakraverty
R. Paul Singh

CRC Press
Taylor & Francis Group
6000 Broken Sound Parkway NW, Suite 300
Boca Raton, FL 33487-2742

© 2014 by Taylor & Francis Group, LLC
CRC Press is an imprint of Taylor & Francis Group, an Informa business

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Version Date: 20130111

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Dedicated to

our parents

vii

Contents

Preface.......................................................................................................... xxv
Introduction............................................................................................... xxvii

Part I
GraIn ProPertIes, DryInG, anD Dryers

1
Properties of Grains................................................................................3
Structure ......................................................................................................3
Chemical Composition................................................................................5
Effects of Temperature on the Quality of Grain............................................6

Proteins .............................................................................................6
Starch ................................................................................................6
Fats ....................................................................................................6
Vitamins............................................................................................6

Physical Properties .......................................................................................7

Sphericity...........................................................................................7
Bulk Density......................................................................................7
True Density......................................................................................7
Porosity .............................................................................................8

Coefficient of Friction and Angle of Repose .................................................9

Coefficient of Friction........................................................................9
Angle of Repose.................................................................................9

Thermal Properties.......................................................................................9

Specific Heat....................................................................................10
Specific Heat Measurement..............................................................10
Thermal Conductivity......................................................................11
Thermal Conductivity Measurement................................................12

Aerodynamic Properties .............................................................................13
Resistance of Grain Bed to Airflow.............................................................14
Symbols .....................................................................................................15

viii ◾ Contents

2
Psychrometry........................................................................................17
Humidity...................................................................................................17
Percentage Humidity..................................................................................18
Relative Humidity......................................................................................18
Humid Heat ..............................................................................................19
Enthalpy ....................................................................................................19
Humid Volume..........................................................................................19
Saturated Volume.......................................................................................19
Dew Point..................................................................................................20
Wet Bulb Temperature ...............................................................................20
Wet Bulb Theory........................................................................................20
Introduction of Psychrometric Chart..........................................................21

Use of Psychrometric Chart .............................................................22

Problems on Psychrometry.........................................................................24

Solved Problems...............................................................................24

Exercises.....................................................................................................29
Symbols .....................................................................................................29

3
Theory of Grain Drying........................................................................31
Thin Layer Drying .....................................................................................31
Moisture Content ......................................................................................32
Moisture Measurement ..............................................................................33

Direct Methods................................................................................33

Single Stage Method...........................................................33
Double Stage Method.........................................................33
Other Methods...................................................................33
Brown–Duvel Distillation Method.....................................33

Indirect Methods ............................................................................ 34

Electrical Resistance Method ............................................. 34
Dielectric Method ............................................................. 34

Equilibrium Moisture Content.................................................................. 34

Determination of EMC ...................................................................35
EMC Models...................................................................................35
Hysteresis.........................................................................................38
Bound Moisture...............................................................................38
Unbound Moisture..........................................................................38
Free Moisture...................................................................................39

Constant Rate Period..........................................................39
Falling Rate Period .............................................................43

Drying Equations ........................................................................... 44

Determination of Drying Constant............................................................48

Contents ◾ ix

Remarks on Thin-Layer Drying Equations.................................................49
Drying Models...........................................................................................50
Effects of Different Factors on the Drying Process......................................50

Effects of Air Temperature ...............................................................52
Effects of Air Velocity.......................................................................52
Effects of Air Humidity....................................................................53
Effects of Air Exposure Time............................................................53

Deep Bed Drying.......................................................................................53

Time of Advance of Drying Front....................................................54
Decreasing Rate Period ....................................................................54

Remarks on Deep Bed Drying....................................................................57

Mass and Heat Balance in Grain Drying..........................................57

Mass Balance......................................................................57
Heat Balance ......................................................................59

Dryer Performance...........................................................................59

Thermal Efficiency..............................................................59
Heat Utilization Factor.......................................................60
Coefficient of Performance .................................................60
Relationship between HUE and COP ................................60
Effective Heat Efficiency.....................................................60

Problems on Moisture Content and Drying ...............................................61

Solved Problems on Moisture Content.............................................61
Exercises ..........................................................................................63
Solved Problems on Drying ............................................................ 64
Exercises ..........................................................................................71

Symbols .....................................................................................................72

4
Methods of Grain Drying.....................................................................75
Conduction Drying ...................................................................................75
Convection Drying ....................................................................................76

Natural Air Drying ......................................................................... 77
Supplemental Heat Drying ............................................................. 77
Heated Air Drying...........................................................................78

Radiation Drying.......................................................................................78

Sun Drying......................................................................................78
Infrared Drying................................................................................79

Solar Drying ..............................................................................................79

Integrated Hybrid-Type Solar Grain Dryer ......................................80

Dielectric and Microwave Drying ..............................................................80
Chemical Drying .......................................................................................81
Sack Prying ................................................................................................81

x ◾ Contents

5
Grain Dryers.........................................................................................83
Unheated Air Dryers..................................................................................83
Storage Unit.............................................................................................. 84

Round Metal Bin............................................................................ 84
Screen Tunnel Quonset-Type Storage Unit...................................... 84

Aeration System .........................................................................................87
Air Distribution System .............................................................................88
Heated Air Dryers......................................................................................89

Flat Bed–Type Batch Dryer..............................................................89

Construction......................................................................89
Operation...........................................................................91

Recirculatory Batch Dryer (PHTC Type).........................................92

Construction......................................................................92
Operation...........................................................................92

Louisiana State University Dryer................................................................93

Construction ...................................................................................93

Rectangular Bin..................................................................96
Air Distribution System......................................................96
Grain Discharging Mechanism ...........................................96
Air Heating System.............................................................96

Baffle Dryer................................................................................................97

Construction ...................................................................................97
Operation........................................................................................98

Rotary Dryer..............................................................................................99

Construction .................................................................................100
Operation......................................................................................100

6
Selection, Design, Specifications, and Testing of Grain Dryers..........103
Selection of Dryers...................................................................................103

Preliminary Dryer Selection...........................................................103

Comparison of Dryers..............................................................................104

Drying Test....................................................................................104

Final Selection of Dryer ...........................................................................105
Design of Grain Dryers............................................................................105

Size, Shape, and Type of Dryer.......................................................106
Calculation of Air, Heat, and Fuel Requirements for Heated Air

Dryers...............................................................................107

Drying Air Temperature.................................................................109
Grain Parameters ...........................................................................109

Airflow Pattern and Air Distribution........................................................109
Conveying and Handling System.............................................................109
Air Heating System ..................................................................................110
Testing of Grain Dryers............................................................................110

Contents ◾ xi

Simple Method..............................................................................110

Simple Test Procedure for Continuous Flow Dryer...........110

Rigorous Method...........................................................................111

Checking of Construction ................................................111
Drying Performance Test ..................................................111
Blower Performance Test...................................................111
Performance of the Control System ..................................112
Performance of the Handling Equipment.........................112
Investigation after Disassembling......................................112

Specifications ...........................................................................................112
Problems on Dryer Design.......................................................................117

Solved Problems.............................................................................117

Exercises...................................................................................................126
Symbols ...................................................................................................127

Part II
GraIn storaGe

7
Food Grain Storage.............................................................................131
Grain Storage Principles...........................................................................132

General .........................................................................................132

Moisture .........................................................................132
Temperature .....................................................................134

Changes in Food Grains during Storage ...................................................134

Chemical Changes.........................................................................134
Physiological Changes....................................................................136

Respiration.......................................................................136
Longevity .........................................................................137
Sprouting .........................................................................137
Heating
.........................................................................138

Biological Changes.........................................................................138

Moisture Migration ..........................................................138
Grain Storage Pests and Their Control..............................139

Types of Grain Spoilage............................................................................139

Reduction in Mass.........................................................................139
Spoilage of Grains by Heating........................................................140
Reduction in Seed Germination.....................................................140
Contamination of Grains by Insects...............................................140

Detection of Insect Infestation .................................................................140
Grain Storage Pests...................................................................................140
Important Insect Species ..........................................................................141
Control of Stored Food Grain Pests..........................................................141
Preventive Measures .................................................................................142

xii ◾ Contents

Curative Measures....................................................................................142

Physical Methods...........................................................................142

Heating
.........................................................................142

Radiation .........................................................................142

Mechanical Methods......................................................................143
Chemical Methods.........................................................................143
Biological Methods........................................................................143

Fumigation ..............................................................................................143

Insecticides ....................................................................................143
Principles of Fumigation................................................................144

Diffusion .........................................................................144
Sorption .........................................................................144
Penetration.......................................................................144
Lethal Effect.....................................................................145

Applications of Fumigants........................................................................145
Rodent Control........................................................................................145

Rat and Mice in Stored Grains.......................................................145
Rodenticides (for Rats and Mice)...................................................146

Food Grain Storage Structures..................................................................146

Rural Storage Structures.................................................................146

Steel Bin .........................................................................147
Aluminum Bin .................................................................147
RCC Bin .........................................................................147
Bag and Bulk Storage........................................................148
Stack Plan.........................................................................148
Dunnage .........................................................................149
Silos ..................................................................................149

Expert System .......................................................................................... 151

Optimal Configurations of Silos ....................................................153
Grain Pressure Theories..................................................................154

Economics of Storage...............................................................................157

Storage in Godowns.......................................................................157
Storage in Silos ..............................................................................157
Cost of Storage in Traditional Godowns and Modern Silos............157

Part III
ParboIlInG anD MIllInG

8
Parboiling of Grain.............................................................................161
Principles .................................................................................................162

Soaking/Hydration ........................................................................163
Soaking Temperature, Duration, and pH.......................................163
Pneumatic Pressure and Reduced Pressure......................................165

Contents ◾ xiii

Hydration Equations................................................................................166
Steaming..................................................................................................169
Drying .....................................................................................................169
Milling.....................................................................................................170
Product Qualities .....................................................................................171
Methods of Parboiling..............................................................................171

Traditional Methods ......................................................................171

Single Boiling/Steaming Process .......................................172
Double Boiling/Steaming Process.....................................172

Improved Methods ........................................................................172

Rice Conversion Process (United Kingdom).....................173
Schule Process (Germany) ................................................173
Crystallo Process (Italy) ....................................................173
Malek Process (United States)...........................................173
Jadavpur University Method (India) .................................174
CFTRI Method (India) ....................................................174
Pressure Parboiling Method (India) ..................................175

9
Parboiling of Wheat............................................................................179
Principles of Parboiling of Wheat.............................................................179

Soaking ..........................................................................................179
Steaming (Cooking).......................................................................181
Drying ...........................................................................................181

Methods of Parboiling and Production of Bulgur.....................................182

Method I: Batch Method...............................................................182
Method II: Preheat Treatment Process............................................183
Method III: Continuous Process....................................................183
Method IV: Chemical Lye Peeling Process .....................................185

Soaking ............................................................................185
Tempering........................................................................186
Cooking ...........................................................................186
Lye Treatment...................................................................186
Peeling ..............................................................................186
Acid Treatment.................................................................187
Drying ..............................................................................187

10
General Grain Milling Operations......................................................189
Cleaning/Separation.................................................................................189

Classification of Separation Methods .............................................189

Separation according to Aerodynamic Properties ..............190
Separation according to Specific Gravity...........................190

xiv ◾ Contents

Separation according to Magnetic Properties ....................190
Separation according to Electrostatic Properties................191
Separation according to Colors (Electronic Separators).....191
Separation according to Surface Properties

(Frictional Separators).......................................192

Effectiveness of the Separation .......................................................194

Husking/Scouring/Hulling of Grain.........................................................194

Methods of Husking......................................................................194

Concave-Type Husker ......................................................194
Husking by the Action of Rubber Rolls ............................196
Husking by Under Runner Disk Husker (Disk Sheller) ....198
Husking by Scourers and Blade-Type Huskers..................199
Hulling by an Abrasive Drum in a Cylindrical Steel Shell .....200

Factors Affecting the Effectiveness of Hulling/Husking/Scouring.......201
Effectiveness of Hulling/Husking/Scouring....................................202

Grinding..................................................................................................202

Effectiveness of Grinding ...............................................................203
Machinery Used in Cereal Grinding ............................................. 204

Grinding of Grain in Roller Mills.................................... 204
Grinding Grain in Hammer Mills ................................... 206

Symbols .................................................................................................. 206

11
Hydrothermal Treatment/Conditioning of Cereal Grains..................207
Physicothermal Properties ....................................................................... 208

Strength/Hardness ........................................................................ 208
Density and Hardness................................................................... 208
Hysteresis...................................................................................... 208
Thermal Properties........................................................................ 208

Biochemical Properties............................................................................ 208
Physicochemical Properties ..................................................................... 208
Effects of Various Factors on the Changes of Different Properties.............209

Effects of Moisture Content...........................................................209
Effects of Temperature ...................................................................209
Thermal Properties.........................................................................209
Chemical Kinetics..........................................................................210
Coefficient of Expansion................................................................210
Biochemical Properties...................................................................210
Optimum Conditions....................................................................210

12
Rice Milling........................................................................................211
Traditional Rice Milling Machinery .........................................................211

Single Huller..................................................................................211