food concentration methods

1. LIQUID CONCENTRATION
 EVAPORATION
 MEMBRANE SEPRATIONS
 FREEZE CONCENTRATION

2. Vocabulary
 Concentration, dehydration, vital,
evaporation , membrane concentration.
freeze concentration, reverse osmosis,
ultrafiltration, fruit juices or purees,
semiporous membrane, permeability,
ice crystal slurry, coffee and tea extracts,
volatile flavors and aromas, centrifugal
force, droplets, entrained, agitation,
buoyancy, gravity,

3. Vocabulary
 flexibility viscosity sanitation bulk
transport semipermeable equilibrate
equilibrium migrate osmotic pressure
feed permeate retentate solution solute
solvent flux solubility polarization

4. Concentration of liquid foods
 Concentration of liquid foods is a vital
operation in many food processes.
Concentration is deferent from
dehydration,. Generally, foods that are
concentrated remain in the liquid state,
whereas drying produces solid or
semisolid foods with significantly lower
water content.

6. Liquid Concentration
Technologies
 Several technologies are available for
liquid concentration in the food industry,
with the most common being
evaporation and membrane
concentration. Freeze concentration is
another technology that has been
developed over the past few decades,
although significant applications of
freeze concentration of foods are limited.

8. Evaporation Concentration
 Evaporation concentration means removal of
water by boiling. Evaporation finds application
in a variety of food processing operations. A
primary application is concentration of fruit
juices (orange juice concentrate), vegetable
juices (tomato pastes and purees), and dairy
products (condensed milk). Evaporation is
also used to concentrate salt and sugars prior
to refining.

9. Membrane Separation
Concentration
 The basis for membrane separations is the
difference in permeability of a semiporous
membrane to different molecular sizes.
Smaller molecules pass through these
membranes more easily than larger ones.
Since water is one of the smallest molecules,
concentration is easily accomplished using
membranes with appropriate molecular-
weight cutoffs.

10. Freeze Concentration
 Water is partially frozen to produce an
ice crystal slurry in concentrated
product. Separation of ice crystals is
then accomplished using some washing
technique. Current applications of
freeze concentration are limited to fruit
juices, coffee, and tea extracts, and
beer and wine. Freeze concentration
produces a superior product

11. Requirements for optimal
evaporation
 (l) rapid rate of heat transfer.
 (2) low-temperature operation through
application of a vacuum.
 (3) efficient vapor-liquid separation.
 (4) efficient energy use and recovery.

12. Types of Evaporators
 Short tube or Calandria Evaporator.
 Long Tube Vertical Rising Film Evaporator
 Long Tube Vertical Falling Film
Evaporator
 Forced Circulation Evaporator.
 Wipe Film or Agitated Thin Film
Evaporator.
 Plate Evaporator.
 Centrifugal/Conical Evaporator.

13. Short tube Evaporator
 A short but wide steam chest in the form
of a shell and tube heat exchanger
characterize this type of evaporator.
Steam is fed to the inside of the internal
tubes. Circulation is generated naturally.
Density differences due to heating
around the steam pipes cause the
warmer fluid to rise and the colder fluid
to sink. A vacuum source maintains to
reduce boiling temperature.

16. Long Tube Vertical Rising Film
Evaporator
 A thin film of liquid food is formed on the
inside of the long tubes, with steam
providing heat transfer from the outside.
The vaporizing bubbles of steam cause
film of concentrate to rise upwards
inside the tubes. Vapor and concentrate
are separated, as they exit the top, in a
separate chamber.

18. Long Tube Vertical Falling
Film Evaporator
 Using gravity to make liquid flow
downwards. Steam condensing on the
outside of the tubes causes evaporation
of a thin film of product flowing down the
inside of the tubes. Product and steam
exit the bottom of the tubes together,
then are separated.

21. Forced Circulation Evaporator
 Fluid is pumped from the main evaporator
chamber through an external steam chest.
Vapor-liquid separation occurs in the main
chamber, Dilute feed is added to the
recirculation loop, and sent through the steam
chest
 Since external pumping is used to maintain
fluid flow, excellent heat transfer can be
obtained, But, recirculation of the fluid
through the steam chest causes long
residence times

23. Wipe Film or Agitated Thin
Film Evaporator
 Very viscous foods are difficult to
evaporate efficiently using any of the
previously discussed evaporators.
Products such as thick fruit or vegetable
purees, or even highly concentrated
sugar syrups, can be efficiently
evaporated when a thin film at the heat
transfer surface is continuously agitated
or wiped to prevent buildup.

25. Plate Evaporator
 A series of metal plates and frames forms the
heat exchange surface both product and
steam are directed in alternate gaps.
Evaporation can take place within the plate
and frame system, or evaporation can be
suppressed by maintaining sufficient pressure
and allowing evaporation to occur as the
heated product flashes into a lower pressure
chamber.

26. Evaporator Configurations
 Single Effect Evaporation
 Multiple Effect Evaporation.
 Thermal Vapor Recompression.
 Mechanical Vapor Recompression.

28. Single Effect Evaporation
 The simplest mode of evaporation is to use a
single stage, where steam is fed into the
steam chest, concentrate and vapor are
removed, and the vapor is condensed into hot
water.
 However, the vapors produced are still steam,
and thus can be used to provide the heat for
evaporation in a subsequent stage. Therefore,
steam can be used many times to provide
evaporation in a series of operations.

30. multiple-effect evaporation
 In a two-stage evaporator, the vapors
produced by evaporation of water in the
first stage are fed into the steam chest
of the second stage to provide further
evaporation. Since there is no driving
force. Thus, operating pressure in the
second stage must be reduced to lower
the boiling temperature

32. Thermal Vapor Recompression
 The quality of the vapors produced during
evaporation can be recompressed. One
alternative is to use fresh steam to enhance
the value of a portion of the vapors. This
combined steam is then fed into the steam
chest. High pressure steam is passed
through a nozzle (or ejector) before entering
the evaporator chamber. As the fresh steam
passes through the nozzle.

34. Mechanical Vapor
Recompression
 Mechanical compression can be used to
improve the quality of vapors. The vapors
from a single stage are compressed to higher
pressure in a mechanical compressor and
then reused as steam in the steam chest .
Reuse of compressed vapors makes up most
of the steam addition. Only a small portion of
fresh steam is needed to account for
inevitable energy losses. Steam economies
can be obtained.

35. MEMBRANE SEPRATIONS
 Operation Principles
 Reverse Osmosis.
 Concentration polarization.
 Ultrafitration.

36. MEMBRANE SEPRATIONS
 Membranes allow only certain molecules to
pass through, effectively separating water
molecules from other food constituents,
 Classification of membrane separations is
based primarily on molecular size. reverse
osmosis/ ultra/micro filtration.
 No vapor-liquid interface to cause the loss of
volatile flavors and aromas
 Membranes tend to foul

37. Operation Principles
 Separations in semipermeable
membrane systems is based on forcing
some of the molecules in the system
through the membrane while retaining
others on the feed side while larger
molecules remain on the feed side
(retentate).

38. difference between reverse osmosis and
ultrafiltration
 The difference between reverse osmosis and
ultrafiltration or microfiltration is the size of
molecules that can pass through the
membrane. Reverse--osmosis membranes
allow only the smallest molecules (Water,
some salts, and volatile compounds) to pass
through, whereas ultrafiltration and
microfiltration limit only the largest molecules
(i.e., proteins, starches, gums, etc.) and allow
all smaller molecules to pass through.

39. MEMBRANE SYSTEMS
 Membrane Materials
 Cellulose Acetate.
 Polymer membranes.
 Composite or Ceramic Membranes.
 Membrane Module Design
 Plate and frame.
 Spiral Wound.
 Tubular.
 Hollow Fiber.

42. Osmotic Pressure
 A salt solution and pure water are
separated with a semipermeable
membrane. Water migrates from the
pure water into the saltwater. As this
equilibrium is attained, the pressures on
the two sides of the membrane are
unequal, The difference in pressure
between the two sides is the osmotic
pressure.

43. Factors Influencing Osmotic
Pressure
 Type of solutes (smaller molecules or
larger molecules)
 Concentration.
 Salts and sugars influenced osmotic
pressure mainly.

44. Osmotic Pressure of Dilute
Solution
 C=solute concentration
 Mw=molecular weight of solute
 R=gas constant
w
M
cRT



46. Reverse Osmosis
 To cause an increase in concentration
of the salt solution , the pressure of the
salt must be raised above the osmotic
pressure. When the applied pressure on
the salt side exceeds the osmotic
pressure, water molecules begin to flow
from the saltwater into the pure water.
This is called reverse osmosis.

48. reverse osmosis process
 Feed under high pressure, exceeding the
osmotic pressure of the feed, contacts the
membrane. Material that passes through it is
the permeate, while material that does not
pass through the membrane, is retentate.
Since membranes are not perfectly selective,
they allow some smaller solute molecules to
pass through; the permeate is not pure water

49. Solvent Flux in Reverse Osmotic
Processing
 Kw=membrane permeability factor
 ΔP=pressure differential across the
membrane
 Δπ= difference in osmotic pressure
between feed and permeate
)
( 


 P
K
J w

50. Mass Flux of Solute
 Ns=mass flux of solute through membrane
 Ks= membrane permeability coefficient
 Cf &Cp=solute concentration in feed and
permeate respectively
)
( p
f
s
s C
C
K
N 


51. Definition of solute rejection
parameter
 A solute rejection parameter, R, is
defined as the ratio of the amount of
solute that passes through the
membrane divided by the initial feed
concentration.
f
p
f
C
C
C
R



53. Concentration Polarization
 Molecules that do not get through the
membrane accumulate on the feed side.
A boundary layer is built up at the
membrane surface due to this solute
rejection. Concentrations of factors 1.2
to 2 higher than the initial feed
concentration can be developed in this
polarization layer

54. Negative Influences of
Concentration Polarization
 The pressure driving force is reduced, so
solvent flux is reduced In addition, solute flux
is increased.
 Concentration buildup often leads to severe
fouling on the membrane surface. When the
concentration in this polarization layer
exceeds the solubility concentration of the
salt it precipitates and forms a more solid
layer. This layer has reduced permeability.

55. Techniques Reducing Polarization
 The feed should be as clear of insoluble
solids as possible. Citrus juice concentration
by reverse osmosis requires an initial filtration
step to remove the pulp.
 Techniques that result in higher flow
velocities across the membrane "sweep"
away the concentration polarization layer and
maximize permeate flux.
 Reduced concentrations in the feed also
result in reduced polarization layer.

56. Factors Influencing Flux in
Reverse Osmosis
 1.Transmembrane pressure (ΔP)
 2.Type of feed material (concentration
molecular weight of solute)
 3.Temperature (Higher temperature
gives lower viscosity and reduces
concentration polarization)
 4.Feed concentration
 5.Feed flow rate (polarization layers)

58. Ultrafiltration
 Ultrafiltration use higher permeability
membranes allowing small molecules to pass
through and retain larger molecules.
 Larger molecules are retained and dissolved
sugars and salts pass through.
 In the dairy industry, ultrafiltration is used to
concentrate milk or whey, allowing everything
but the proteins to pass through.

61. MEMBRANE SYSTEMS
 Membrane Materials
 Cellulose Acetate/Polymer membranes/
Composite or Ceramic Membranes.
 Membrane Module Design
 Plate and frame/Spiral Wound/Tubular/
Hollow Fiber.

62. Cellulose Acetate
 The membranes provide high permeate flux
and good salt rejection in reverse osmosis.
However, cellulose acetate breaks down at
high temperatures, is pH sensitive (pH 5 to 6),
and is broken down by Cl- ions. Since
chlorine cleaners and sanitizers are
commonly used in the food industry, the
sensitivity of cellulose acetate membranes to
chlorine has caused significant problems.

63. Polymer membranes
 Polyamides provide better pH resistance than
cellulose acetate. Polysulfones provide a
good alternative, operate at a wide pH range
(1 to 15), and have chlorine resistance (up to
50 ppm). They are easy be produced with a
wide range of pore size cutoffs. But, these
membranes do not withstand high pressures
and are used almost exclusively for ultra-
filtration

64. Composite or Ceramic Membranes
 These membranes are made from
porous carbon, zirconium oxide, or
alumina. Due to the inert nature of the
composite materials, membranes made
from these materials have a wide range
of operating conditions (temperature,
pH). They are also resistant to chlorine
attack and can be cleaned easily.

65. Membrane Module Design
 Membranes can be packaged in many
ways to provide options for separation.
The main categories include:
 Plate-and-frame arrangement
 Spiral-wound membranes,
 Tubular membranes
 Hollow-fiber membranes.

68. Spiral Wound
 Rolling up a flat membrane and spacer
system into a spiral-wound package Feed is
distributed to the appropriate channels at one
end of the roll; permeate passes through the
membrane and makes its way back around
the spiral to a collector tube at the center of
the roll. Permeate then passes out the center,
while retentate is collected at the opposite
end.

70. Tubular
 A cylindrical membrane and support
system is housed inside a larger tube.
Feed is pumped into the center of the
tube under applied pressure; permeate
passes through the membrane system
and is collected in the outside tube.
Retentate passes directly through the
membrane and is removed from the
opposite side.

72. Hollow Fiber
 A bundle of smaller membrane tubes
(only millimeters in diameter) containing
hundreds of individual tubes may be
housed in a single larger shell. Feed is
directed into the tubes at one end, while
concentrate is removed at the other end.
Permeate passing through the
membranes is collected from the shell
side of the housing.

73. CLEANING AND
SANITATION
 Mild acids and bases with nonionic
surfactants, enzymes, and complexing
agents are used to clean membranes
 Clean-in-place systems can be used to
clean membrane modules, with the
most rapid flow rate possible to induce
turbulence at the membrane surface.

74. FOOD QUALITY IN
MEMBRANE OPERATIONS
 Because low temperature operation,
thermal degradation of nutrients does
not occur.
 The quality of foods processed using
membrane systems is generally
superior to that produced using other
concentration technologies

75. FREEZE CONCENTRATION
 TYPES OF FREEZE CONC. UNITS
 Ice Crystallization
 Direct Contact Freezers.
 Indirect-Contact freezers
 Separation Devices
 Mechanical Press
 Centrifugal.
 Wash Column.
 ECONOMIC DESIGN OF FREEZE
CONCENTRATION

76. Definition of Freeze Concentration
 A liquid food is cooled with sufficient
agitation, ice crystals nucleate and grow,
and a slurry of relatively pure ice
crystals removed, The concentrate can
be obtained. Separation of these pure
ice crystals leaves a concentrated
product.

77. Advantages & Disadvantage of
Freeze Concentration
 High product quality due to low-
temperature operation
 Absence of a vapor-liquid interface
maintaining original flavors.
 Higher cost of than the other two.

78. Employed on Wide Range of
Products
 Fruit juices, milk products, vinegar,
coffee and tea extracts, beer and wine,
and other flavor products.
 Concentration of alcoholic beverages is
one application where freeze
concentration is superior to other
techniques.

80. Freezing-point Depression
 Products containing low-molecular
weight compounds, like sugars and
salts, experience a reduction in freezing
point as product is concentrated.

82. TYPES OF FREEZE
CONCENTRATION UNITS
 Ice Crystallization
 Direct Contact Freezers
 Indirect-Contact freezers
 Separation Devices
 Mechanical Press
 Centrifugal
 Wash Column.

85. Problem
 How to obtain high quality food product
in evaporation concentration.
 How to lower the cost in liquid
concentration operation.

86. Problem
 Describe the principles of both evaporation
and membrane concentration
 What are the differences between reverse
osmosis and ultra-filtration.
 How to understand the membrane materials
 How to consider the membrane module
design

87. Problem
 Explain the principles of freeze
concentration
 How to understand the operation of
freeze concentration
 What are the advantages of freeze
concentration and how to to obtain food
in high quality economically.