Pasteurisation does not completely sterilise the milk but merely reduces the number of bacteria present to a low level. At this stage the mix will be harmless unless the bacteria are allowed to multiply and to avoid this multiplication, it is essential that the mix is cooled as soon as possible. The regulations insist that the mix is cooled to 45°F or lower within 1½ hours of pasteurisation. At this stage, the mix should be thin enough to flow over or through the tubes of the cooler.

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