Treatment of Milk
Some treatments given to milk are:
Filtered milk goes through an extra fine filtration system, which prevents bacteria from passing through. The nutritional content of the milk is unaffected but the shelf life is increased. The milk is then homogenised and evenly distributes the fat molecules.
Filtered milk is available in whole, semi-skimmed or skimmed milk varieties.
Evaporated milk is a concentrated, sterilised milk product. It has a concentraion twice that of standard milk. The process of producing evaporated milk involves standardising, heat treating and evaporating the milk under reduced pressure.
The evaporated milk is then homogenised to prevent it from separating, under storage and then it is cooled.
Louis Pasteur believed that milk soured because of the presence of bacteria. He showed by experiment that if heated the souring process could be delayed and the milk could be safer to drink. The aim of pasteurisation is to destroy harmful bacteria without affecting the flavour and quality of milk.
The milk is heated to about 72°C for at least 15 seconds, then cooled rapidly to about 10°C. This is known as the flash process or the high temperature. The milk is heated to 63°C for half an hour, then cooled rapidly. This is known as the Holder Method.
NOTE: Milk must be cooled rapidly to prevent:
(i) destruction of nutritive value
(ii) bacterial growth
This means that the temperature has been raised and the milk treated for much longer. The flavour is altered and the cream line disappears altogether, but the milk will keep unopened for months and days.
Further treatment at high temperature will result in the milk which will have a considerably long life and does not need to be kept in a refrigerator. This milk comes in cartons and is expensive.
Tuberculin tested Milk
This milk is produced by cows which are tested, to ensure that they are free from tuberculosis, at intervals, of 2 to 6 months. The milk from these special herds must be labelled to indicate this.
Ultra heat treatment (U.H.T)
Fresh milk is heated to 132°C for one second, then cooled rapidly. This can be done by passing it directly through heat or steam. After this treatment, the milk must be packed under sterile conditions.
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