Raw milk on arrival at the factory is rapid tested for temperature, hygiene, antibiotics, water addition and
adulteration.
On acceptance the milk is pumped into a silo storage tank at the processing plant and held at temperatures below
7 C and usually below 5 C.
Raw whole milk has varying Fat & Solids Not Fat (SNF) content and typically between 3.5% and 4.5% Fat and 8% to 9%
SNF giving typical Total Solids of 12.5%. Developing countries are milk solids usually lower and care should be taken in
ensuring that costs / yields are calculated accurately for any planned high volume dairy manufacturing plant and
we suggest you prepare a very detailed yield spreadsheet., use the calculator on the link above to view the effect of
0.1% protein or moisture variation on annual milk powder production yield and milk powder profitability.
Milk is mostly collected in insulated tankers from dairy farms or milk collection stations. Prior to collection the driver will
carry out quality and measurement tests to ensure the milk is of the required quality.
Adulteration of raw milk in some countries is prolific and a real barrier to globally operating companies establishing
facilities due to the high brand risk involved.
When the raw milk arrives at the manufacturing plant it is usually separated into cream and skimmed milk to enable
standardization of the fat content prior to spray drying. High volume manufacturers will automate this cream fat
standardization using an inline “standomat” which doses cream back into the skim to give the correct fat % in the
milk to be processed.
Some high volume plants particularly in the US also standardise the SNF content to maximise yields and give a
consistent quality.
The microbial quality of milk powders is very important and it is possible at this early stage of processing to take out
99.9% of the spore-forming bacteria by either bacto-fugation or microfiltration prior to heat treatment.
This is a the ideal next stage but many processors primarily due to cost do not include this stage.
Both processes require that the milk is first separated and then the skimmed milk portion has the bacteria removed
and the cream is them high temperature pasteurised and returned to the milk (if required)
This is the method used for ESL milk (Extended Shelf Life). Infant Formula manufactures operating in developing
countries should use a bactofuge or microfiltration plant to ensure finished produt quality.
The milk is high temperature short-time pasteurized (HTST) by heating to at least 72 C, and holding at or above this
temperature for at least 15 seconds, (An equivalent temperature / time combination can be used). Most high
volume liquid milk plants now operate on a higher holding time of 25 to 35 as a precaution over the possible survival
of MAP which can cause Crohn’s disease in humans.
(Mycobacterium avium subspecies paratuberculosis may be capable of surviving pasteurization.)
Heat treatment affects the functional properties of skim milk powder and the keeping quality of whole milk powder,
so the temperature and time combinations used by manufacturers can vary widely depending on the required
properties required of the finished powder.
In skimmed milk powder, the extent of heat treatment (and holding time) can be measured by the whey protein
nitrogen index (WPNI), which measures the amount of un-denatured whey protein.
Skimmed milk powder processing differs from whole milk and buttermilk processing by the heat treatment given to
skim milk before evaporation.
The skimmed milk heat treatment temperature coupled with the holding time determines the heat classification of
the powder produced. For skim milk powder classified as “low-heat”, the milk is low temperature pasteurized with
little or no holding required, while heat treatment for a “high-heat” method requires heating milk to 85-88 C and
holding at this temperature for 15 to 30 seconds..There is no requirement to homogenize skimmed milk for powder
production because of its low fat content. High heat, heat stable powders are also produced by varying the
evaporation conditions.
Homogenisation is not a mandatory step in whole milk or buttermilk processing, but is usually applied in order to
decrease the free fat content.