Published on Jan 19, 2016
Pasteurization rids the milk of any disease-producing organisms and substantially reduces the total bacteria count for improved shelf life. Pasteurization also destroys lipase, alkaline phosphates, and other natural milk enzymes in raw milk.
The Pasteurization temperatures and times are selected to ensure the destruction of mycobacterium tuberculosis and the organism causing Q-fever. A treatment of 145°F for 30 minutes or its equivalent is required to ensure destruction of the bacteria.
The two accepted methods for milk pasteurization include: the batch or holding method of heating every particle of milk to not less than 145°F and holding at this temperature for not less than 30 minutes, or the high temperature-short time (HTST) method of heating every particle of milk to not less than 161°F and holding for not less than 15 seconds. Most dairies now use the HTST method.
Batch pasteurization is carried out in heated vats provided with an agitator to ensure uniform heating, a cover to prevent contamination during the 30-minute holding period, and a recording thermometer to trace a permanent record of the time-temperature treatment. Batch pasteurization of milk has been largely replaced with HTST pasteurization.
High temperature-short time (HTST) pasteurization requires a plate-frame heat exchanger, a holding tube, a flow diversion valve, and time-temperature recording charts. HTST systems also include such additional equipment as a vacuum chamber to remove volatile off flavors from the pasteurized milk, and a homogenizer.
All pasteurization equipment must be of approved design; frequent visits from milk inspectors are a check on proper equipment operation.
The pasteurized milk is not sterile and must be cooled quickly following pasteurization to prevent the multiplication of surviving bacteria. Pasteurization at these temperatures does not produce an objectionable cooked flavor in milk and has no significant effect on its nutritional value.
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