all about homogenization and Homogenizer

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DAIRY SCIENCE COLLEGE HEBBAL
,BENGALURU

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Homogeniser

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 Homogenization is the process of breaking up the fat globules in
cream to such a small size that they remain suspended evenly in milk
rather than separating out and floating to the surface. Homogenizer is
a machine, which disintegrates the fat globules of milk.
DEFINITION OF HOMOGENIZATION

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 It is any of several process used to make a chemical
mixture the same throughout.
 It is intensive mixing of mutually insoluble phase
(sometimes with the addition of surfactants) to obtain
a suspension/emulsion.
 The process of homogenization was invented and
patented by Auguste Gaulin in 1899.
 Homogenization primarily cause disruption of fat
globules into smaller ones.

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 According to the United States Public Health Services
(USPHS), ‘homogenized milk is one that has been treated in
such a manner as to ensure the break-up of the globules to such
an extent that after 48 hours of quiescent storage, no visible
cream separation occurs in milk and the fat percentage of the
milk in the upper 10% portion, i.e., in the top 100 ml of milk in a
quart bottle or of proportionate volumes in containers of other
sizes, does not differ by > 10% of itself from the fat percentage of
the remaining milk, as determined after thorough mixing’.
 The number of fat globules in homogenized milk is about 10,000
times greater than those in un-homogenized milk. The size of fat
globule is reduced to < 1 micron, while normal fat globule size
averages 2 – 12 µm in milk. The number of fat globules will be
increased, but total volume of fat globules will remain almost
same. The surface area of newly formed smaller fat globules is
increased by 4-6 folds.
HOMOGENISED MILK

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 In raw milk, the diameter of the fat particles varies from 2 to 12
µm, while a diameter of about 2 µm or less is required to keep
the fat from rising in stored condition. The milk is forced at
high pressure through a narrow slit (spring loaded valve),
which is only slightly larger than the diameter of the globules.
The velocity of milk in the narrow slit can be 100 - 200 m/s.
This can cause high shearing stresses, cavitation and micro-
turbulence. The globules becomes deformed, wavy and then
breakup.
PRINCIPLES OF HOMOGENIZATION

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Homogenizing valve assembly: The homogenizing valve assembly is essential an
adjustable orifice- or series of adjustable orifices. The pressure created by the
piston pump forces product through the homogenizing valve , causing a very
significant pressure drop across the orifice. The valve design and degree of
pressure drop determine the effect on the product. In general, the greater the
pressure drop, the greater the effect on the particle size of the product being
homogenised.
The homogenizing valve assembly has three crucial smaller components: The
‘Valve’, ‘Valve Seat’, and the ‘Impact Ring’. The Valve and Valve Seat are the
pieces that actually form the orifice. The Impact Ring is a sacrificial piece that
prevents the high pressure annular fan from damaging the chamber that
surrounds it . All three components are made from a special wear-resistant
hardened alloy.

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HOMOGENIZER-CONSTRUCTION
HOMOGENIZER
PISTON
PUMP
HOMOGENIZING
VALVE
GENERATE HIGH
PRESSURE
5 OR 7 PISTONS
POPPET TYPE-
BETTER
PERFORMANCE
BALL TYPE –EXERT
GREATER PRESSURE

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 1)Counteracting creaming:
 To achieve this, the size of the fat globules should be greatly
reduced. A cream layer in the product may be a nuisance for
the user, especially if the package is non-transparent.
 2)Improving stability toward partial coalescence:
 The increased stability of homogenized fat globules is caused
by the reduced diameter and by the acquired surface layer of
the fat globules. Moreover, partial coalescence especially
occurs in a cream layer, and such a layer forms much more
slowly in homogenized products.
Objective/Purpose of Homogenization

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 3)Creating desirable rheological properties:
 Formation of homogenization clusters can greatly
increase the viscosity of a product such as cream.
Homogenized and subsequently soured milk (e.g.,
yogurt) has a higher viscosity than un-homogenized
milk. This is because the fat globules that are now
partly covered with casein micelles in the aggregation
of the casein micelles.
 4)Recombining milk products:
 At one stage of the process, butter oil must be
emulsified in a liquid such as reconstituted skim milk.
A homogenizer, however, is not an emulsifying
machine. Therefore, the mixture should first be pre-
emulsified, for example, by vigorous stirring; the
formed coarse emulsion is subsequently homogenized.

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 1) Turbulence:. Sudden, high velocity directional
changes cause small, intense turbulent eddies to form in
the base liquid. Larger globules are torn apart by these
eddies, reducing the overall average globule size.
 2)Cavitation: When traveling through the small orifice,
the product experiences a considerable increase in
velocity, then a sudden decrease in velocity and pressure.
The rapid velocity & pressure changes cause the base
liquid to suddenly vaporize, then collapse back into a
liquid – a process known as cavitation. The imploding
vapour bubbles further tear apart the fat globules.
Theories of Homogenization

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 3)Shattering & impact
 The fat globules are shattered by impinging them on the
retaining valve or impact ring.
 4)Explosion
 With the release of high pressure, the fat globules explode.
 5)Shearing & grinding
 The fat globules are subjected to unequal forces as milk
flows at different velocities in a fluid stream. As a result of
the shearing action between globules, it deforms the fat
globules beyond its yield point.
 6)Attenuation
 The fat globule disruption is attributed to violent changes
in the velocities of milk as it passes through the unit
rendering a fragmentation slight effect on the mean
particle size.

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 1)High pressure homogenizer
 This type of homogenizer consists of single acting triplex
pump with each cylinder having suction and discharges
valves. The discharge valve of each pump empties into a
common discharge pipe, in which a special valve is placed.
The pressure ranges between 35 – 350 bar (500-5000 psi)
depending on the type of construction of the valve.
 2)Low pressure-rotary type homogenizers
 Usual operating pressures are below 35 bar (500 psi). The
construction is so designed that milk is subjected to
grinding and shearing action.
 3)Sonic vibrators- milk is subjected to high frequency
vibration in a device called sonic vibrator or oscillator.
Types of Homogenizer

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Sonic vibrators
Low pressure homogenizer-
Operating pressures : below 35
bar(500 psi)
High pressure homogenizer-
Pressure ranges between 35 -350 bars

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 Homogenization effect is achieved by pushing liquid (milk)
under a very high pressure through a very narrow orifice,
whose diameter is just slightly larger than the diameter of
fat globules.
 When the liquid passes through the narrow gap the flow
velocity increases.
 The speed will increase until the static pressure is so low
that liquid starts to boil.
 The maximum speed depends on the inlet pressure.
When liquid leaves the gap the speed decreases and the
pressure increases again.
 The liquid stops boiling and steam bubbles implode
(collapse)
Homogenization Process

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 Homogenization can be done in two ways:
 1. Single Stage 2. Two Stage
 In single stage & two stage homogenization
the total homogenization pressure is
measured before the first stage P1 & the
homogenization pressure in 2nd stage is
measured before the 2nd stage P2.
 The 2 stage method is usually chosen to
achieve optimum homogenization/efficiency.
 Best results are obtained when P2/P1=0.2
 In first stage pressure is around 2000-
2500psi & 2nd stage 500- 1000psi.
 Temperature is 120ºF
 In 1st stage fat globules join together to form
clumps and is known as Post clumping.
 Single stage homogenization may be used
for production of high viscosity
product.(Cream)

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1.Complete Homogenization – E.g. Milk
2. Partial Homogenization – E.g. Cream
Homogenization can be:

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Full stream or total homogenization is the most
commonly used form of homogenization of UHT milk
and milk intended for cultured milk products. The fat
content of the milk is standardized prior to
homogenization, as is the solids-non-fat content in
certain circumstances, e.g. in yoghurt production.
Full stream homogenization

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Partial homogenization is used to save on energy and machinery.
The milk is separated into skim milk and cream, and the cream is
homogenized and mixed with the separated milk (Walstra et al.,
2006).
Partial stream homogenization means that the main body of skim
milk is not homogenized, but only the cream together with a small
proportion of skim milk. This form of homogenization is mainly
applied to pasteurised market milk. The basic reason is to reduce
operating costs. Total power `consumption is cut by some 80%
because of the smaller volume passing through the homogenizer
(Bylund, 2003).
Partial homogenization

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 The physical state and concentration of the fat phase at
the time of homogenization contribute materially to the
size and dispersion of the ensuing fat globules.
 Cream with higher fat content than 12% cannot be
homogenized because it causes clumping & shortage of
membrane material (Casein). Therefore, a good
homogenization effect requires 0.2g casein per g of fat.
 Temperature during homogenization range from 55 –
80ºC & homogenization pressure is between 10-25Mpa
(100 – 250 bar) depending on the product.
Process Requirements

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 Temperature of Milk: Milk should have above 33C
temperature at the time of homogenization for fat phase in
liquid for proper subdivision.
 Pressure of homogenization: 10-25Mpa (100 – 250 bar).
 Stage of homogenization: For milk with more than 6% fat,
two stage homogenization is better. If the broken up fat
globules have a tendency to agglomerate after the first
homogenizing stage (150-200 bar), they can be re-dispersed
employing 20-40 bar in the second stag.
 Fat content: Homogenization becomes less effective with
increasing fat content. When the fat content is high, raising
the temperature improves homogenization efficiency. When
the fat content is high, the newly created total fat globule
surface is so large that the material (plasma protein)
becomes insufficient to form new membranes on fat.
Factors affecting Homogenization

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 Smaller fat globules leading to no cream-line
formation.
 Whiter and more appetizing color.
 Reduced sensitivity to fat oxidation.
 More full-boiled flavor & better mouth feel.
 Better stability of cultured milk products (Soft curd).
 No formation of cream layer/plug
 Produces soft curd and is better digested; hence
recommended for infant feeding
Effects/Advantages of Homogenization

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 Homogenized milk cannot be efficiently separated.
 Milk will not be suitable for production of semi
hard/hard cheese because the coagulum will be too
soft.
 Reduced heat stability in case of single stage
homogenizer, high fat content & forms clumping of
fat globules.
 More susceptible to ‘sunshine flavor’
Disadvantages

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1) Fresh milk – Creaming of fat is avoided & taste improvement
is achieved.
2) Coffee cream, Evaporated Milk – Avoids creaming improves
whitening power in coffee.
3) Cheese milk – Reduce the fat content of whey, provides a
more uniform fat distribution in the cheese mass, inhibits ‘fat
sweating’ of cheese & enhance the biochemical fat
degradation.
4) Acidified dairy products – Improvement in consistency,
taste, more stable acid gel & reduced whey synergizes in
yoghurt & in other coagulated products.
5) Milk mix beverage – Good distribution of additive & fat.
6) Ice-cream mix – Reduced buttering of fat during freezing
Application of
homogenization

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 Effect of Homogenization on Physico-Chemical Properties of Milk
 Reduction of fat globules size
 Reduction of fat globule size to < 2 µ prevents formation of cream
layer and increases the surface area of the fat about 6 times.
 Whiter milk
 Homogenization of milk increases its whitening power due to an
increase in the number and surface area of the fat globules.
Adsorption of casein miscelles and serum proteins on newly created
fat globules surface increases scattering of light thereby causing whiter
appearance.
 Physiology of nutrition
 Homogenization has been reported to improve the digestibility of
milk due to increase in the number and surface area of the fat globules
EFFECT OF HOMOGENIZATION ON MILK
PROPERTIES

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 Flavor of milk
 Homogenized milk has a uniform flavor throughout. It tastes richer,
smoother and creamier than un-homogenized milk due to an increase in the
surface area of the fat globules which are uniformly distributed in milk.
 Sensitivity to lipase
 Homogenized milk is more susceptible to enzymatic activities, especially
lipase action, than un-homogenized milk. Lipase can cause rancidity rapidly
in homogenized raw milk.
 Susceptibility to oxidation
 Homogenized milk is more susceptible to oxidized flavors caused by
natural or artificial light than un-homogenized milk. To prevent
development of off-flavors, homogenized milk must be packaged in opaque
containers, such as cartons, plastic containers or colored bottles.
 Bacterial count
 There will be an apparent increase in bacterial count after homogenization
due to the break-up of clumps and colonies of organisms.

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