Two stage homogenization is usually used as single stage can result in fat globules coalescing into larger globules
more readily. This is considered important for infant formula manufacturing. Two stage homogenising is preferable to
ensure minimal re-coalescing of globules take place.
Fat globules with damaged protective membranes reduce milk powder solubility and increase the risk of to oxidative
rancidity.
Homogenization helps convert free fat into fat globules and membranes are regenerated by protein adsorption on
the globule surfaces.
Milk powder heat treatment varies depending on the finished product specification. Infant formula milk powder
treatment is higher than most other powders. The aim is to destroy all pathogenic and as many of the other
microorganisms present and to inactivate enzymes, particularly lipase, which can cause fat lipolysis during storage
resulting in "off odours". This also reduces the risk of oxidative changes during storage.
There are special treatments available from certain evaporator manufacturers that can provide a very good
reduction in thermoduric bacteria which tend to grow in evaporators and cause issues with powder quality (High
thermophile counts) Counts vary depending on the time of year and type of feed. (usually winter silage feed
increases thermophillic spore counts in raw milk) Other optional ingredients such as vegetable fats, vitamins and
minerals are added to the milk prior to drying, ensuring appropriate heat treatment
The milk is concentrated in a series of calandrias in an evaporator to around 40-60% total solids, prior to Spray
Drying.Most milk evaporators are today of the falling film type where a fine film of milk / concentrate is passed down
the tubes wetting the surface whilst steam is on the other side of the tube and the vapours extracted from the centre
by vacuum.
Vapours are normally recompressed in a vapour recompressor making evaporators very efficient.
Water from evaporators can be recovered and re used. .
Evaporation of the milk prior to drying is done for reasons of energy efficiency as it is far cheaper to evaporate the
water than to spray dry it. The energy used in multi pass evaporators with steam vapour recompression is about 10
times less than spray drying.