The document discusses homogenization and deaeration processes in dairy production. Homogenization involves forcing milk through a small passage at high pressure, disrupting fat globules from an average of 3.5 μm to below 1 μm. This prevents creaming and improves texture. Deaeration removes air introduced during milking and transport using vacuum expansion to boil off dissolved air, improving measurement accuracy and heat exchanger performance. Both processes enhance quality and efficiency in dairy processing.

1. Building-blocks of
dairy processing

2. The technology behind
disruption of fat globules
• Homogenisation has become a standard
industrial process, universally practised as a
means of stabilising the fat emulsion against
gravity separation
• Homogenisation primarily causes disruption of
fat globules into much smaller ones
• It diminishes creaming and may also diminish
the tendency of globules to clump or coalesce
• Milk is forced through a small passage at high
velocity

3. Homogenisation causes
disruption of fat globules

4. • The disintegration of the original fat globules
is achieved by a combination of contributing
factors such as turbulence and cavitation
• The homogenisation reduces fat globule size
from an average of 3.5 μm indiameter to
below 1 μm
• The newly created fat globules are no longer
completely covered with the original
membrane material

5. • Instead, they are surfaced with a mixture of
proteins adsorbed from the plasma phase
• Casein was the protein half of the complex
and that it was probably associated with the
fat fraction through polar bonding forces
• Casein micelle was activated at the moment it
passed through the valve of the homogeniser,
• predispose it to interaction with the lipid
phase.

6. • The physical state and concentration of the fat
phase at the time of homogenisation
contribute materially to the size & dispersion of
the subsequent fat globules
• Homogenisation of cold milk, in which the fat is
essentially solidified, is virtually ineffective
• Processing at temperatures conducive to the
partial solidification of milk fat (i.e. below 40 °C)
results in incomplete dispersion of the fat phase

7. • Products of high fat content are more difficult
to homogenise and also more likely to show
evidence of fat clumping, because the conc.
of serum proteins is low in relation to the fat
content
• Usually, cream with higher fat content than 20
% cannot be homogenised at high pressure,
clusters are formed as a result of lack of
membrane material (casein)

8. • Increasing the homogenisation temperature
decreases the viscosity of milk and improves
the transport of membrane material to the fat
globules
• Homogenisation temperatures normally
applied are 55 – 80 °C, and homogenisation
pressure is between 10 and 25 MPa (100 –
250 bar), depending on the product

9. Flow characteristics
• When the liquid passes the
narrow gap, the flow velocity
increases
• The speed will increase until
the static pressure is so low
that the liquid starts to boil
• The maximum speed depends
mainly on the homogenisation)
pressure
• When the liquid leaves the gap,
the speed decreases and the
pressure increases again
• The liquid stops boiling and
the steam bubbles collapse

10. Homogenisers may be
equipped with one
homogenising device
or two connected in
series, hence the
names
• Single-stage
homogenisation
and
• Two-stage
homogenisation.

11. Effect of homogenisation
• Smaller fat globules leading to less cream-line
formation
• Whiter and more appetizing colour
• Reduced sensitivity to fat oxidation
• More full-bodied flavour, and better
mouthfeel
• Better stability of cultured milk product

12. The homogeniser in a processing line
• In general, the homogeniser is placed upstream,
i.e. before the final heating section in a heat
exchanger.
• In most pasteurisation plants for market milk
production, the homogeniser is usually placed
after the first regenerative section.
• In production of UHT milk, the homogeniser is
generally placed upstream in indirect systems but
always downstream in direct systems, i.e. on the
aseptic side after UHT treatment

13. The homogeniser in a processing line
• However, downstream location of the homogeniser is
recommended for indirect UHT systems
 when milk products with a fat content higher than
6 – 10 % and/or with increased protein content are
going to be processed.
 with increased fat and protein contents, fat clusters
and/ or agglomerates (protein) form at the very high
heat treatment temperatures.
 These clusters/agglomerates are broken up by the
aseptic homogeniser located downstream.

14. Split homogenisation
An aseptic homogeniser is more
expensive to operate. In some cases it is
sufficient if just the second stage is placed
downstream. This arrangement is called
split homogenisation

15. Partial homogenisation
Partial stream homogenisation means that
the main body of skim milk is not
homogenised, but only the cream together
with a small proportion of skim milk
• This form of homogenisation is mainly applied to
pasteurised market milk.
• The basic reason is to reduce operating costs

16. Determining homogenisation
efficiency
• Homogenisation must always be sufficiently
efficient to prevent creaming
• A sample of milk is stored in a graduated
measuring glass for 48 hours at a temperature
of 4 – 6 °C
• The top layer (1/10 of the volume) is siphoned
off, the remaining volume (9/10) is thoroughly
mixed, and the fat content of each fraction is
then determined

17. • The difference in fat content between the
top and bottom layers, expressed as a of the top
layer, is referred to as the homogenisation index
• An example: If the fat content is 3,15 % in the
top layer and 2,9 % in the bottom layer, the
homogenisation index will be (3,15 – 2,9) x
100: 3,15 =7,9.
• The index for homogenised milk should be in
the range of 1 to 10.

18. Evaporators
• Removal of water
• Concentration of a liquid involves evaporation
of a solvent, in most cases water.
• Concentration is distinguished from drying in
that the final product – the concentrate – is
still liquid

19. Reasons for concentrating food liquids
• Reduce costs for storage and transportation
• Induce crystallisation
• Reduce the cost of drying
• Reduce water activity to increase
microbiological and chemical stability
• Recover valuable substances and by-products
from waste streams

21. Circulation evaporators
• Circulation evaporators can be used when a low
degree of concentration is required or when
small quantities of product are processed.
• In yoghurt production, for example, evaporation
is utilised to concentrate milk 1,1 – 1,25 times, or
from 13 to 14,5 or 16,25 % solids content
respectively
• This treatment simultaneously deaerates the
product and rids it from off-flavours

22. Plate-type evaporator
• Distribution in a plate-type falling-film
evaporator can be arranged with two pipes
running through the plate pack.
• For each product plate there is a spray nozzle
in each product pipe, spraying the product in
a thin, even film over the plate surface.

23. Deaerators

24. • More air is introduced into the milk during handling at
the farm and transportation to the dairy, and during
reception at the dairy.
• It is not unusual for incoming milk to contain 10 % air
by volume, or even more
The basic problems caused by dispersed air are
• Inaccuracy in volumetric measurement of milk.
• Incrustation of heating surfaces in pasteurisers
(fouling).
• Reduced skimming efficiency in separators.
• Loss of precision in automatic in-line standardisation

25. Deaeration in the milk treatment line
• Vacuum deaeration has been used
successfully to expel dissolved air and finely
dispersed air bubbles from milk
• Pre-heated milk is fed to an expansion vessel,
in which the vacuum is adjusted to a level
equivalent to a boiling point about 7 to 8 °C
below the pre-heating temperature
• If the milk enters the vessel at 68 °C, the temp
will immediately drop to 68 – 8 = 60 °C.

26. • The drop in pressure expels the dissolved air,
which boils off, together with certain amount
of the milk.
• The vapour passes a built-in condenser in the
vessel, condenses, and runs back into the
milk,
• while the boiled-off air, together with non
condensable gases (certain off-flavours) is
removed from the vessel by the vacuum pump