Pasteurisation of milk provides protection for the consumer against pathogens which may be present in the raw milk, and improves its keeping quality. Sterilisation provides indefinite keeping quality but has an undesirable effect on the flavour and nutritive value of the milk. Ultra high temperature (UHT) treatment produces a milk with prolonged shelf life at ambient temperatures yet has practically the same effect on colour, falvour and nutritive value as pasteurisation. UHT treatment of milk involves preheating to 80 degrees C and then quickly raising the temperature, either by indirect heating in a tubular heater or by direct steam injection, to 130 degrees-- to 150 degrees C at which temperature it is kept for 3 to 5 sec. Cooling follows immediately. Systems in operation in South Africa use steam injection for heating to sterilising temperatures. Evaporation cooling is obtained by subjecting milk to a partial vacuum. This removes any water added during heating by condensing steam and also removes steam-volatile off-flavours. UHT-treated milk is packed aseptically, usually into heat-sealed paperboard laminated cartons. Intact packages can be kept for up to three months. Absolute sterility cannot be obtained by UHT processing. The term "sterilising effect", introduced by Galesloot, means the log10 of the ratio of initial spore count to surviving spore count. A spoilage rate of not more than one litre package per 1000 is considered satisfactory. For laboratory control samples of the sterilized milk are incubated at temperatures favourable to germination of mesophilic and thermophilic spores respectively. After incubation the milk is examined for flavour and physical appearance, subjected to the standard plate count and tested for increase in acidity and decrease in stability towards the alcohol test. Milk for UHT treatment must possess protein stability in the alcohol test, be of good bacteriological quality, and a low spore count in particular.