Pasteurization can destroy some undesirable enzymes and many spoilage bacteria. The extent of microorganism inactivation depends on the combination of temperature and holding time. Minimum temperature and time requirements for milk pasteurization are based on thermal death time studies for the most heat resistant pathogen found in milk, Coxelliae burnettii . Thermal lethality determinations require the applications of microbiology to appropriate processing determinations. An overview can be found here.
Milk is deemed pasteurized if it tests negative for alkaline phosphatase.
There has also been some progress with low temperature pasteurization methods using membrane processing technology. . There are two basic methods, batch or continuous. The batch method uses a vat pasteurizer which consists of a jacketed vat surrounded by either circulating water, steam or heating coils of water or steam. In the vat the milk is heated and held throughout the holding period while being agitated. The milk may be cooled in the vat or removed hot after the holding time is completed for every particle.