Zeki berk food process engineering and technology

F o o d
a n d

P r o c e s s

E n g i n e e r i n g

T e c h n o l o g y


FOOD PROCESS ENGINEERING AND TECHNOLOGY


Food Science and Technology
International Series
Series Editor
Steve L. Taylor
University of Nebraska - Lincoln, USA
Advisory Board
Ken Buckle
The University of New South Wales, Australia
Mary Ellen Camire
University ofMaine, USA
Roger Clemens
University of Southern California, USA
Hildegarde Heymann
University of California — Davis, USA
Robert Hutkins
University of Nebraska Lincoln, USA
Ron S. Jackson
Quebec, Canada

Huub Lelieveld
Bihkoven, The Netherlands
Daryl B. Lund
University of Wisconsin, USA
Connie Weaver
Purdue University, USA
Ron Wrolstad
Oregon State University, USA

A complete list of books in this series appears at the end of this volum


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Zeki Berk
Professor (Emeritus)
Department of Biotechnology and Food Engineering
TECHNION
Israel Institute ofTechnology
Israel
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ELSEVIER
Academci Press is an imprint of Elsevier
PARIS

SAN D I E C 0

SAN


To my students

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C o n t e n t s

Introduction - Food is Life
1
1 Physical properties of food materials 7
1 -1 Introduction
7
1.2 Mechanical properties
8
1.2.1 Definitions
8
1.2.2 Rheological models
9

1.3 Thermal properties
10
1.4 Electrical properties
11
1.5 Structure
11
1.6 Water activity
13
1.6.1 The importance of water in foods
13
1.6.2 Water activity, definition and determination
14
1.6.3 Water activity: prediction
14
1.6.4 Water vapor sorption isotherms
16
1.6.5 Water activity: effect on food quality and stability
19
1.7 Phase transition phenomena in foods
19
1.7.1 The glassy state in foods
19
1.7.2 Glass transition temperature
20
2 Fluid flow 27
2.1 Introduction
27
2.2 Elements of fluid dynamics
27
2.2.1 Viscosity

27
2.2.2 Fluid flow regimes
28
2.2.3 Typical applications of Newtonian laminar flow
30
2.2.3a Laminar flow in a cylindrical channel (pipe or tube) 30
2.2.3b Laminar fluid flow on flat surfaces and channels
33
2.2.3c Laminar fluid flow around immersed particles
34
2.2.3d Fluid flow through porous media
36
2.2.4 Turbulent fluid flow
36
2.3 2.3.2
2.3.1
Flow properties
T
Non-Newtonian
2.2.4a
(tube
2.2.4b
ypes or
ofTurbulent
Turbulent
fluid
pipe)
of fluids
flow
fluid

Newtonian
fluid
behavior
flow
flowin around
fluid
pipesflow
imm
inerasedcylindrical
particleschannel
344
741
0039


vi Contents
2.4 Transportation of fluids
2.4.1 Energy relations, the Bernoulli Equation
2.4.2 Pumps: Types and operation
2.4.3 Pump selection
2.4.4 Ejectors
2.4.5 Piping
2.5 Flow of particulate solids (powder flow)
2.5.1 Introduction
2.5.2 Flow properties of particulate solids
2.5.3 Fluidization
2.5.4 Pneumatic transport
3 Heat and mass transfer, basic principles 69
3.1 Introduction
3.2 Basic relations in transport phenomena

3.2.1 Basic laws of transport
3.2.2 Mechanisms of heat and mass transfer
3.3 Conductive heat and mass transfer
3.3.1 The Fourier and Fick laws
3.3.2 Integration of Fourier's and Fick's laws for
steady-state conductive transport
3.3.3 Thermal conductivity, thermal diffusivity
and molecular diffusivity
3.3.4 Examples of steady-state conductive heat and
mass transfer processes
3.4 Convective heat and mass transfer
3.4.1 Film (or surface) heat and mass transfer coefficients
3.4.2 Empirical correlations for convection heat and mass
transfer
3.4.3 Steady-state interphase mass transfer
3.5 Unsteady state heat and mass transfer
3.5.1 The 2nd Fourier and Fick laws
3.5.2 Solution of Fourier's second law equation for an
infinite slab
3.5.3 Transient conduction transfer in finite solids
3.5.4 Transient convective transfer in a semi-infinite body
3.5.5 Unsteady state convective transfer
3.6 Heat transfer by radiation
3.8
7 3.8.1
3.6.1
3.6.2
3.6.3
3.
M

H7eic.a1
2
4
3rtow
ex
Overall
Fouling
Radiation
H
B
Interaction
av
cah
esaictnheating
geprinciples
exrcoefficient
cshachno
begm
eaetw
tb
rseib
nof
x
eein
n
ctd
w
hof
m
aethe

matter
n
with
eich
g
nre
oaw
food
flowing
tbconvection
aetransfer
vatw
endep
heating
erno
thermal
fluids
ce
surfaces
ss industry
radiation

43
43
46
52
55
56
56
56

57
62
65
69
69
69
70
70
70
71
73
76
81
81
84
87
89
89
90
92
94
95
96
1100
1410
7
1090
9872
1
60005

Contents vii
3.9 Ohmic heating
3.9.1 Introduction
3.9.2 Basic principles
3.9.3 Applications and equipment
4 Reaction kinetics 115
4.1 Introduction
4.2 Basic concepts
4.2.1 Elementary and non-elementary reactions
4.2.2 Reaction order
4.2.3 Effect of temperature on reaction kinetics
4.3 Kinetics of biological processes
4.3.1 Enzyme-catalyzed reactions
4.3.2 Growth of microorganisms
4.4 Residence time and residence time distribution
4.4.1 Reactors in food processing
4.4.2 Residence time distribution
5 Elements of process control 1 29
5.1 Introduction
5.2 Basic concepts
5.3 Basic control structures
5.3.1 Feedback control
5.3.2 Feed-forward control
5.3.3 Comparative merits of control strategies
5.4 The blockdiagram
5.5 Input, output and process dynamics
5.5.1 First order response
5.5.2 Second order systems

5.6 Control modes (control algorithms)
5.6.1 On-off (binary) control
5.6.2 Proportional (P) control
5.6.3 Integral (I) control
5.6.4 Proportional-integral (PI) control
5.6.5 Proportional-integral-differential (PID) control
5.6.6 Optimization of control
5.7 The physical elements of the control system
5.7.1 The sensors (measuring elements)
5.7.2 The controllers
5.7.3
T
6 Size
6..1
6
2 6.2.4
6.2.3
6.2.1
6.2.2
Particle
Introduction
reduction
A
Mathematical
defining
Particle
Defining
shizenote
eactuators
and

son
ai153
the
zeparticle
m
'particle
distribution
sem
iazn
eodof
particle
esliszah
eofPSD
asingle
pdistribution
einsize'
a particle
population of particles;

109
109
110
112
115
116
116
116
119
121
121

1 22
123
123
1 24
1 29
1 29
131
131
131
1 32
132
133
133
1 35
1 36
1 36
138
139
140
140
141
142
142
149
115143591
81554
5
6
45
0

viii Contents
6.3 Size reduction of solids, basic principles
6.3.1 Mechanism of size reduction in solids
6.3.2 Particle size distribution after size reduction
6.3.3 Energy consumption
6.4 Size reduction of solids, equipment and methods
6.4.1 Impact mills
6.4.2 Pressure mills
6.4.3 Attrition mills
6.4.4 Cutters and choppers
7 Mixing 175
7.1 Introduction
7.2 Mixing of fluids (blending)
7.2.1 Types of blenders
7.2.2 Flow patterns in fluid mixing
7.2.3 Energy input in fluid mixing
7.3 Kneading
7.4 In-flow mixing
7.5 Mixing of particulate solids
7.5.1 Mixing and segregation
7.5.2 Quality of mixing, the concept of'mixed ness'
7.5.3 Equipment for mixing particulate solids
7.6 Homogenization
7.6.1 Basic principles
7.6.2 Homogenizers
8 Filtration 195
8.1 Introduction
8.2 Depth filtration

8.3 Surface (barrier) filtration
8.3.1 Mechanisms
8.3.2 Rate offiltration
8.3.3 Optimization of the filtration cycle
8.3.4 Characteristics offiltration cakes
8.3.5 The role of cakes in filtration
8.4 Filtration equipment
8.4.1 Depth filters
8.4.2 Barrier (surface) filters
8.5 Expression
9 Centrifugation
9..1
9
2 9.2.4
9.2.1
9.2.2
9.2.3
B
8.5.1
8.5.2
8.5.3
Introduction
asic principles
T
Applications
F
Liquid-liquid
M
Introduction
rhoem

chcontinuous
baffled
athe
nis21
msettling
s asettling
7
separation
ndsettling
etank
qutank
ipm
totank
en
athe
n
td the
tubular
disc-bowl
centrifuge
centrifuge

163
163
163
163
165
1 66
167
168

170
1 75
175
175
177
1 78
181
1 84
1 84
1 84
184
187
189
189
191
195
196
198
198
199
204
205
206
207
207
207
211
222
121
7

21
48138
222203


Contents i>
9.3 Centrifuges
9.3.1 Tubular centrifuges
9.3.2 Disc-bowl centrifuges
9.3.3 Decanter centrifuges
9.3.4 Basket centrifuges
9.4 Cyclones
10 Membrane processes 233
10.1 Introduction
10.2 Tangential filtration
10.3 Mass transfer through MF and UF membranes
1 0.3.1 Solvent transport
1 0.3.2 Solute transport; sieving coefficient and rejection
1 0.3.3 Concentration polarization and gel polarization
1 0.4 Mass transfer in reverse osmosis
10.4.1 Basic concepts
1 0.4.2 Solvent transport in reverse osmosis
1 0.5 Membrane systems
10.5.1 Membrane materials
10.5.2 Membrane configurations
10.6 Membrane processes in the food industry
10.6.1 Microfiltration
10.6.2 Ultrafiltration
10.6.3 Nanofikration and reverse osmosis
10.7 Electrodialysis

11 Extraction 259
11.1 Introduction
11.2 Solid -liquid extraction (leaching)
11.2.1 Definitions
11.2.2 Material balance
11.2.3 Equilibrium
1 1.2.4 Multistage extraction
11.2.5 Stage efficiency
11.2.6 Solid-liquid extraction systems
11.3 Supercritical fluid extraction
11.3.1 Basic principles
11.3.2 Supercritical fluids as solvents
11.3.3 Supercritical extraction systems
11.
3h.1
4adsorption
Applications
12 Adsorption
12.
111.2.
2
4
31 Adsorption
B
Equilibrium
Liquid-liquid
Introduction
atc4
2
Principles

and
inconditions
extraction
colu
ion
mnsexchange 279

226
227
228
230
230
231
233
234

235
235
237
238
241
241
242
245
245
247
249
249
249
251

253
259
261
261
262
262
262
266
268
271
271
272
273
227
27
85
6
8
76
0
27
9


x Contents
12.5 Ion exchange
1 2.5.1 Basic principles
1 2.5.2 Properties of ion exchangers
1 2.5.3 Application: Water softening using ion exchange
12.5.4 Application: Reduction of acidity in fruit juices

13 Distillation 295
13.1 Introduction
13.2 Vapor-liquid equilibrium (VLE)
13.3 Continuous flash distillation
13.4 Batch (differential) distillation
1 3.5 Fractional distillation
13.5.1 Basic concepts
13.5.2 Analysis and design of the column
13.5.3 Effect of the reflux ratio
13.5.4 Tray configuration
13.5.5 Column configuration
13.5.6 Heating with live steam
13.5.7 Energy considerations
13.6 Steam distillation
13.7 Distillation of wines and spirits
14 Crystallization and dissolution 317
14.1 Introduction
14.2 Crystallization kinetics
14.2.1 Nucleation
14.2.2 Crystal growth
14.3 Crystallization in the food industry
14.3.1 Equipment
14.3.2 Processes
14.4 Dissolution
14.4.1 Introduction
1 4.4.2 Mechanism and kinetics
1 5 Extrusion 333
15.1 Introduction
15.2 The single-screw extruder
15.2.1 Structure

15.2.2 Operation
1 5.2.3 Flow models, extruder throughput
15.
15
4.3Effect
F
15.
1
T
oo5.2.4
5.5.1
5.3.3
w
4
3d.i1
2n-applications
socStructure
C
Operation
P
nreA
R
Formi
hw
yfoods
ee
dsm
sv
icextruders
daie

cnlantgalceffects
geeffect
eextrusion
of
stime
aextrusion
nddistribution
shortcomings
of pasta

288
288
289
292
293
295
295
298
301
304
304
305
310
310
311
311
312
313
314
317

318
318
320
323
323
325
328
328
328
333
334
334
335
337
334340
23
44
5
3
00
3
5


Contents xi
1 5.5.2 Expanded snacks
345
1 5.5.3 Ready-to-eat cereals
346
15.5.4 Pellets

347
1 5.5.5 Other extruded starchy and cereal products
347
15.5.6 Texturized protein products
348
1 5.5.7 Confectionery and chocolate
348
15.5.8 Petfoods
349
16 Spoilage and preservation of foods 351
16.1 Mechanisms of food spoilage
351
1 6.2 Food preservation processes
351
1 6.3 Combined processes (the 'hurdle effect')
353
16.4 Packaging
353
1 7 Thermal processing 355
17.1 Introduction
355
17.2 The kinetics of thermal inactivation of microorganisms and
enzymes
356
1 7.2.1 The concept of decimal reduction time
356
17.2.2 Effect of the temperature on the rate of thermal
destruction/inactivation
358
17.3 Lethality of thermal processes

360
1 7.4 Optimization of thermal processes with respect to quality
363
1 7.5 Heat transfer considerations in thermal processing
364
1 7.5.1 In-package thermal processing
364
17.5.2 fn-flow thermal processing
369
18 Thermal processes, methods and equipment 375
1 8.1 Introduction
375
18.2 Thermal processing in hermetically closed containers
375
18.2.1 Filling into the cans
376
1 8.2.2 Expelling air from the head-space
378
18.2.3 Sealing
379
18.2.4 Heat processing
380
1 8.3 Thermal processing in bulk, before packaging
386
18.3.1 Bulk heating - hot filling - sealing - cooling in container 386
18.3.2 Bulk heating holding - bulk cooling - coldfilling- sealing 386
18.3.3 Aseptic processing
388
19 Refrigeration, chilling and freezing 391
19.1 Introduction

391
1
9
.
2
Effect
of
temperature
o
n
food
spoilage
3336
9
19.3 F
19.3.1
19.2.4
19.2.5
1re9.2.2
19.2.3
9.2.1
ezingT
(respiring)
P
Effect
T
h
Effect
eaesm
eeffect

ptransition,
ofeof
ralotutissue
lw
oof
rewtemperature
loatemperature
w
ndfreezing
temperature
chemicalpoint
o
on
noactivity
nmicroorganisms
biologically
oennzyphysical
matic active
spoilage
properties 43090401
8
39
299295


xii Contents
19.3.2 Freezing kinetics, freezing time
19.3.3 Effect of freezing and frozen storage on product
quality
20 Refrigeration, equipment and methods 413

20.1 Sources of refrigeration
20.1.1 Mechanical refrigeration
20.1.2 Refrigerants
20.1.3 Distribution and delivery of refrigeration
20.2 Cold storage and refrigerated transport
20.3 Chillers and freezers
20.3.1 Blast cooling
20.3.2 Contact freezers
20.3.3 Immersion cooling
20.3.4 Evaporative cooling
21 Evaporation
21.1 Introduction
21.2 Material and energy balance
21.3 Heattransfer
21.3.1 The overall coefficient of heat transfer U
21.3.2 The temperature difference T -T (AT)
21.4 Energy management
21.4.1 Multiple-effect evaporation
21.4.2 Vapor recompression
21.5 Condensers
21.6 Evaporators in the food industry
21.6.1 Open pan batch evaporator
21.6.2 Vacuum pan evaporator
21.6.3 Evaporators with tubular heat exchangers
21.6.4 Evaporators with external tubular heat exchangers
21.6.5 Boiling film evaporators
21.7 Effect of evaporation on food quality
21.7.1 Thermal effects
21.7.2 Loss of volatile flavor components
22 Dehydration 459

22.1 Introduction
22.2 Thermodynamics of moist air (psychrometry)
22.2.1 Basic principles
22.3 22.3.5
C
22.3.2
22.3.3
22.3.4
22.2.2
22.2.3
22.2.4
22.2.5
22.3.1
onvectiT
v
Adiabatic
Calculation
Effect
Saturation,
Humidity
Deheewdrying
falling
constant
drying
point
of external
saturation,
(air
relative
of

crate
urrate
drying
vdrying)
epconditions
hp
ahumidity
shetime
wet-bulb
ase (RH)
ontemperature
the drying rate

402
408
413
413
418
419
420
423
423
425
426
426

429

s

c

429
430
432
433
436
440
441
446
447
448
448
449
449
451
451
454
454
457
459
461
461
461
4446
47663
7244
2
7
4

075


Contents xiii
223.6 Relationship between film coefficients in convective drying... 476
22.3.7 Effect of radiation heating
477
22.3.8 Characteristic drying curves
477
478
22.4 Drying under varying external conditions
22.4.1 Batch drying on trays
478
22.4.2 Through-flow batch drying in a fixed bed
480
22.4.3 Continuous air drying on a belt or in a tunnel
481
22.5 Conductive (boiling) drying
481
22.5.1 Basic principles
481
22.5.2 Kinetics
482
22.5.3 Systems and applications
483
22.6 Dryers in the food processing industry
485
22.6.1 Cabinet dryers
486
22.6.2 Tunnel dryers

487
22.6.3 Belt dryers
489
22.6.4 Belt-trough dryers
489
22.6.5 Rotary dryers
490
22.6.6 Bin dryers
490
22.6.7 Grain dryers
492
22.6.8 Spray dryers
492
22.6.9 Fluidized bed dryer
497
22.6.10 Pneumatic dryer
498
22.6.11 Drum dryers
499
22.6.12 Screw conveyor and mixer dryers
500
22.6.13 Sun drying, solar drying
501
22.7 Issues in food drying technology
501
22.7.1 Pre-drymg treatments
501
22.7.2 Effect of drying conditions on quality
502
22.7.3 Post-drying treatments

503
22.7.4 Rehydration characteristics
503
22.7.5 Agglomeration
504
22.8 Energy consumption in drying
504
22.9 Osmotic dehydration
507
23 Freeze drying (lyophilization) and freeze concentration 511
23.1 Introduction
511
23.2 Sublimation ofwater
511
23.3 Heat and mass transfer in freeze drying
51 2
23.
4
F
r
e
e
z
e
drying,
in
practice
5
1
24 Frying,

24.
23.15 Introduction
23.5.1
23.5.2
F
23.4.1
23.4.2
23.4.3
23.4.4
reezbaking,
e concentration
T
F
B
Drying
h
raeeseiz
ceipnrprinciples
godryers
drying,
conditions
roasting
cess ofcommercial
freeze
525
concentration
facilities
551
21
28

55
8
0
912818


xiv Contents
24.2 Frying
24.2.1 Types of frying
24.2.2 Heat and mass transfer in frying
24.2.3 Systems and operation
24.2.4 Health aspects of fried foods
24.3 Baking and roasting
25 Ionizing irradiation and other non-thermal preservation processes
25.1 Preservation by ionizing radiations
25.1.1 Introduction
25.1.2 Ionizing radiations
25.1.3 Radiation sources
25.1.4 Interaction with matter
25.1.5 Radiation dose
25.1.6 Chemical and biological effects of ionizing irradiation
25.1.7 Industrial applications
25.2 High hydrostatic pressure preservation
25.3 Pulsed electric fields (PEF)
25.4 Pulsed intense light
26 Food packaging
26.1 Introduction
26.2 Packaging materials
26.2.1 Introduction
26.2.2 Materials for packaging foods

26.2.3 Transport properties of packaging materials
26.2.4 Optical properties
26.2.5 Mechanical properties
26.2.6 Chemical reactivity
26.3 The atmosphere in the package
26.3.1 Vacuum packaging
26.3.2 Controlled atmosphere packaging (CAP)
26.3.3 Modified atmosphere packaging (MAP)
26.3.4 Active packaging
26.4 Environmental issues
27 Cleaning, disinfection, sanitation
27.1 Introduction
27.2 Cleaning kinetics and mechanisms
27.2.1 Effect of the contaminant
27.
2
2
Effect
the
support
27.6
27.
7
4
5
3 O
Cleaning
27.2.4
Kinetics
d5

o.r1
5
3abCleaning
aofof
tem
disinfection
plants
rpaa
ew
c
nofktamaterials
in
out
m
geaesnpcdltemperature
cleaning
of
h
aacn
epq
iclaua(CIP)
clipem
action
(aC
egnO
etnPt)(shear)

525
525
526

527
528
528
533
533
533
533
534
535
537
538
540
541
542
542
545
545
546
546
548
551
553
554
555
556
556
557
557
557
558

561
561
562
562
4
55
7
656
1
768
606
4


Contents xv
Appendix
Table A.1 Common conversion factors
Table A.2 Typical composition of selected foods
Table A.3 Viscosity and density of gases and liquids
Table A.4 Thermal properties of materials
Table A.5 Emissivity of surfaces
Table A.6 US standard sieves
Table A.7 Properties of saturated steam - temperature table
Table A.8 Properties of saturated steam - pressure table
Table A. 9 Properties of superheated steam
Table A.10 Vapor pressure of liquid water and ice below 0°C
Table A.11 Freezing point of ideal aqueous solutions
Table A.1 2 Vapor-liquid equilibrium data for ethanol-water
mixtures at 1 atm
Table A.13 Boiling point of sucrose solutions at 1 atm

Table A.14 Electrical conductivity of some materials
Table A.1 5 Thermodynamic properties of saturated R-134a
Table A.1 6 Thermodynamic properties of superheated R-134a
Table A.1 7 Properties of air at atmospheric pressure
Figure A.1 Friction factors for flow in pipes 587
Figure A.2 Psychrometric chart
Figure A.3 Mixing power function, turbine impellers
Figure A.4 Mixing power function, propeller impellers
Figure A.5 Unsteady state heat transfer in a slab
Figure A.6 Unsteady state heat transfer in an infinite cylinder
Figure A.7 Unsteady state heat transfer in a sphere
Figure A.8 Unsteady state mass transfer, average concentration
Figure A.9 Error function
Index 593
Series List

575
576
577
578
578
579
579
580
581
581
582
583
583
584

584
584
585
586
587
588
588
589
589
590
590
591
603



I n t r o d u c t i o n

'Food is Life'

Wc begin this book with the theme of the 13th World Congress of the Intern
Union of Food Science and Technology (ILJFoST), held in Nantes, France, in
September 2006. in recognition of the vital role of food and food processing in our
life. The necessity to subject the natural food materials to some kind of treatment
before consumption was apparently realized very early in prehistory. Some of these
operations, such as the removal of inedible parts, cutting, grinding and cooking, aimed
at rendering the food more palatable, easier to consume and to digest. Others had as
their objective the prolongation of the useful life of food, by retarding or preventing
spoilage. Drying was probably one of the first operations of this kind to be practiced.
To this day, transformation and preservation are still the two basic objectives of food

processing. While transformation is the purpose of the manufacturing industry in general, the objective of preservation is specific to the processing of foods.
The Food Process
Literally, a 'process' is defined as a set of actions in a specific sequence, t
cific end. A manufacturing process starts with raw materials and ends with products
and by-products. The number of actually existing and theoretically possible processes
in any manufacturing industry is enormous. Their study and description individually
would be nearly impossible. Fortunately, the 'actions' that constitute a process may
be grouped in a relatively small number of operations governed by the same basic
principles and serving essentially similar purposes. Early in the 20th century, these
operations, called unit operations, became the backbone of chemical engineering
studies and research (Loncin and Merson, 1979). Since the 1950s, the unit operation approach has also been extensively applied by teachers and researchers in food
CopyrighBruin
t V 20a0
lsevier Inc.2003).
FopordocP
s Engineering a(Fellows,
nd Technolo1
gy988; Bimbenet et al., 2002:
ersoscesengineering
n9d. E
Jongen,
Al
l
r
i
g
h
t
s
r

e
searvbeld
ISS
Bo
Nm
: e97S
0
1
2
3
7
3
6
6
0
4
of the unit operations of the food processing industry are listed in T
e 1.1.


2 Introduction
Table 11
. Unit operations of the foodsinpgreindustry by principal groups
Examples of application
Group
Unit operation
Fruits, vegetables
Cleaning
Washing
Fruits, vegetables

Peeling
Removal of foreign bodie Grains
Cleaning in place (CIP) All food plants
Sugar refining
Filtration
Centrifugatic
Grains
P
r
e
s
s
i
n
g
,
e
x
p
Coffee beans
Molecular (diffusion based)
Adsorption
Ultrafiltration of whey
separation
Di
s
t
i
l
a

t
i
o
n
Separation of milk
Mechanical transformatio
Extraction
Oilseeds, fruits
Bleaching of edible oils
Agglomeration
Alcohol production
Coating, encapsulat
Vegetal oils
Cooking
Chocolate refining
Baking
Beverages, dough
Frying
Mayonnaise
Fermentation
Mi
Preservation (Note: Many of the unit
Paslkte,ucrrieamnlk
Aging, curing
C
ookies, pasta
operations listed underP
' reservation'
Extrusion cooking
M

wedaetr, fish
F
r
eilkshpom
also serve additional purposes such a
Thermal processing
C
Froznefnectiodninenryers
cooking, volume and mass reduction
(blanching, pasteuri
M
Iceeactream
improving the flavor etc.)
sterilization)
Concentration
B
bg
reeatadbles
Froiszceunits,ve
Chiling
P
t
a
t
o
fries
T
o
m
a

t
o
p
Addition
of solutes aste
Freezing
W
Citrinues, jb
ueiceer, cyoongcuertntrate
Chemical preservation
C
Suhgeaerse, wine
B
t cereals
Sareltiankgfasoffish
Dehydration
Jams, preserves
Pickles
Salted fish
Smoked fish
Freeze dryin
Dried fruit
Packaging
Filing
Dehydrated vegetables
Sealing
Milk powder
Wrapping
Instant coffee
M

stn
po
oo
areatso
C
Inraeo
B
F
sn
satah
lh
eneedd
tdsacblfa
o
ed
fv
fsetd
gesflakes


Batch and Continuous Processes 3

While the type of unit operations and their sequence vary from one process to
another, certain features are common to all food processes:
• Material balances and energy balances are based on the universal principle o
the conservation of matter and energy
• Practically every operation involves exchange of material, momentum and/or
heat between the different parts of the system. These exchanges are governed
by rules and mechanisms, collectively known as transport phenomena
• In any manufacturing process, adequate knowledge of the properties of the

materials involved is essential. The principal distinguishing peculiarity of food
processing is the outstanding complexity of the materials treated and of the
chemical and biological reactions induced. This characteristic reflects strongly
on issues related to process design and product quality and it calls for the extensive use of approximate models. Mathematical - physical modeling is indeed
particularly useful in food engineering. Of particular interest are the physical
properties of food materials and the kinetics of chemical reactions
• One of the distinguishing features of food processing is the concern for food
safety and hygiene. This aspect constitutes a fundamental issue in all the phases
of food engineering, from product development to plant design, from production to distribution
• The importance of packaging in food process engineering and technology cannot be overemphasized. Research and development in packaging is also one of
the most innovative areas in food technology today
• Finally, common to all industrial processes, regardless of the materials treated
and the products made, is the need to control. The introduction of modern measurement methods and control strategies is, undoubtedly, one of the most significant advances in food process engineering of the last years.
Accordingly, the first part of this book is devoted to basic principles, comm
Batch and Continuous Processes
food processes and includes chapters on the physical properties of foods, momentum
transfer (flow),may
heat an
dm
ass transfer, reaction
kineticscontinuous
and elements ofor
procmixed
ess con- fashion.
Processes
be
carried-out
in batch,
trol.
he restprocessing,

of the book deals
with theofprincipal
unit operations
In T
batch
a portion
the materials
to be proof
cesfood
sed processing.
is separated from
the bulk and treated separately. The conditions such as temperature, pressure, composition etc. usually vary during the process. The batch process has a definite duration
and, after its completion, a new cycle begins, with a new portion of material. The
batch process is usually less capital intensive but may be more costly to operate and
involves costly equipment dead-time for loading and unloading between batches. It is
easier to control and lends itself to intervention during the process. It is particularly


4 Introduction

suitable for small-scale production and to frequent changes in product composition
and process conditions. A typical example of a batch process would be the mixing of
flour, water, yeast and other ingredients in a bowl mixer to make a bread dough. After
having produced one batch of dough for white bread, the same mixer can be cleaned
and used to make a batch of dark dough.
In continuous processing, the materials pass through the system continuously
without separation of a part of the material from the bulk. The conditions at a given
point of the system may vary for a while at the beginning of the process, but
ally they remain constant during the best part of the process. In engineering terms, a
continuous process is ideally run at steady state for most of its duration. Continuous

processes are more difficult to control, require higher capital investment, but provide better utilization of production capacity, at lower operational cost. They are
particularly suitable for lines producing large quantities of one type of product for a
relatively long duration. A typical example of a continuous process would be the continuous pasteurization of milk.
Mixed processes are composed of a sequence of continuous and batch processe
An example of a mixed process would be the production of strained infant food. In
this example, the raw materials are first subjected to a continuous stage consisting of
washing, sorting, continuous blanching or cooking, mashing andfinishing(screening). Batches of the mashed ingredients are then collected in formulation tanks wh
they are mixed according to formulation. Usually, at this stage, a sample is sent to the
quality assurance laboratory for evaluation. After approval, the batches are pumped,
one after the other, to the continuous homogenization, heat treatment and packaging
line. Thus, this mixed process is composed of one batch phase between two continuous phases. To run smoothly, mixed processes require that buffer storage capacity
provided between the batch and continuous phases.
Process Flow Diagrams
Flow diagrams, also called flow charts or flow sheets, serve as t
cal representation of processes. In its simplest form, a flow diagram shows the major
operations of a process in their sequence, the raw materials, the products and the byproducts. Additional information, such asflowrates and process conditions such as
temperatures and pressures may be added. Because the operations are conventionally
shown as rectangles or 'blocks',flowcharts of this kind are also called block diagrams. Figure 1.1 shows a block diagram for the manufacture of chocolate.
A more detailed description of the process provides information on the main pieces
of equipment selected to perform the operations. Standard symbols are used for frequently utilized equipment items such as pumps, vessels, conveyors, centrifuges, filthe
tersOther
included.
is
not
actual
etc.drap(Figure
w
T
iehnc
qeeusito

presulting
m
ofscale
1.
en
2
etq).uoripam
drawing
nidentified
denh
t aasren
isobrepresented
called
ymaeanlegend.
in
ang equipment
w
byhP
atrcsou
ocsee
to
vsm
esr concerning
piping
symbols,
flowisdiagram.
schematically
resembling
the location
A

fairly
offlow
thedi


Process Flow Diagrams 5

Figure 12
. Some symbols used in process flow diagrams: 1: Reactor; 2: Distilation column; 3: Heat
exchanger; 4: Plate heat exchanger; 5: Filter or membrane, 6: Centrifugal pump; 7: Rotary positive
displacement pump; 8: Centrifuge


Fig" ; 13
. Pictorial Flo

of chocolate manufacturing process (Courtesy of Buhler AC)

equipment in space. A simplified pictorial equipment flow diagram for the chocolate
production process is shown in Figure 1.3.
The next step of process development is the creation of an engineering flow d
gram. In addition to the items shown in the equipment flow diagram, auxiliary or secondary equipment items, measurement and control systems, utility lines and piping
details such as traps, valves etc. are included. The engineering flow diagram serves as
a starting point for the listing, calculation and selection of all the physical elements of
aReferences
food plant or production line and for the development of a plant layout.

Bimbenct. J.J., Duquenoy, A. and Trystram, G. (2002). Geni
Dunod, Paris.
Bruin, S. and Jongen, Th.R.tJ. (2003). Food process engineering; the last 25 years and

challenges ahead. Comprehens Rev Food Sci Food Safety 2, 42-54.
Fellows, P.J. (1988). Food Processing Technology. F.llis Horwood Ltd New York.
Loncin. M. and Mcrson, R.L. (1979). Food Engineering, Principles and Selected
Applications. Academic Press. New York.


P h y s i c a l
F o o d

P r o p e r t i e s

o f

M a t e r i a l s

1.1 Introduction

Dr Alina Szczesniak defined the physical properties of foods as 'those prop
that lend themselves to description and quantification by physical rather than chemical means' (Szczesniak, 1983). This seemingly obvious distinction between physical
and chemical properties reveals an interesting historical fact. Indeed until the 1960s.
the chemistry and biochemistry of foods were by far the most active areas of food
research. The systematic study of the physical properties of foods (often considered
a distinct scientific discipline called 'food physics' or 'physical chemistry of foods")
is of relatively recent origin.
The physical properties of foods are of utmost interest to the food engineer, mainly
for two reasons:
• Many of the characteristics that define the quality (e.g. texture, structure,
appearance) and stability (e.g. water activity) of a food product are linked to its
physical properties
• Quantitative knowledge of many of the physical properties, such as thermal

conductivity, density, viscosity, specific heat, enthalpy and many others, is
essential for the rational design and operation of food processes and for the
prediction of the response of foods to processing, distribution and storage conditions. These are sometimes referred to as 'engineering properties', although
most physical properties are significant both from the quality and engineering
points of view.
In recent years, the growing interest in the physical properties of foods is c
spicuously manifested. A number of books and reviews dealing specifically with the
subject
an
Jowitt,
htd<'Bagley,
2009. Els1983;
evier Inc.
Food Proch
esasveEnb
ge
ineen
eringpublished
and Techno(e.g.
logy Mohsenin. 1980; PeCleogpyrig
1983;
Lewis,
1990;
R
a
h
m
a
n
,

1
9
9
5
;
Balint,
2001:
Scanlon,
2001;
S
a
h
i
n
a
n
d
S
All rights reserved umnu,
ISBN: 978-0-12-373660-4
2006; Figura and Teixeira, 2007). The number of scientific meetings on related


8 Physical Properties of Food Materials
subjects held every year is considerable. Specific courses on the subject are being
included in most food science, engineering and technology curricula.
Some of the 'engineering' properties will be treated in connection with the unit
operations where such properties are particularly relevant (e.g. viscosity influidflow,
particle size in size reduction, thermal properties in heat transfer, diffusivity in mass
transfer etc.). Properties of more general significance and wider application are discussed in this chapter.

1.2 Mechanical Properties

1.2.1 Definitions
By mechanical properties, we mean those properties that determine the behavior of
food materials when subjected to external forces. As such, mechanical properties are
relevant both to processing {e.g. conveying, size reduction) and to consumption (texture, mouth feel).
The forces acting on the material are usually expressed as stress, i.e. intensity o
the force per unit area (N.m or Pa.). The dimensions and units of stress are like
those of pressure. Very often, but not always, the response of materials to stress is
deformation, expressed as strain. Strain is usually expressed as a dimensionless
ratio, such as the elongation as a percentage of the original length. The relationship between stress and strain is the subject matter of the science known as rheolog
(Steffe,
19%). deformation: deformation appears instantly with the application of str
• Elastic
Weandefine
three
typeswith
of deformation
d disap
pearsideal
instantly
the removal(Szczesniak,
of stress. F1983):
or many materials, the
strain is proportional to the stress, at least for moderate values of the deformation. The condition of linearity, called Hookes' law (Robert Hooke. 1635-1703,
English scientist) is formulated in Eq. (1.1):
_ stress _ \
strain
where
E = Youngs' modulus (after Thomas Young, 1773-1829, English scientist). Pa

F = force applied N
A = original cross-sectional area
AL = elongation, in
) = original
length.
• L,
Plastic
deformation:
deformation does not occur as long as the stress is
a limit value known as yield stress. Deformation is permanent, i.e. the body
does not return to its original size and shape when the stress is removed.
2

E

0