Pasteurization

Pasteurization is a process in which liquids are heated to a specified temperature for a specified length of time to kill or retard the growth of bacteria and other disease-causing microorganisms. It is named for the French scientist Louis Pasteur, who along with Claude Bernard performed the first test of pasteurization in 1862. Although pasteurization is most familiar in its [Page 1343]application to milk today, Pasteur's original work was concerned with the process of fermentation used in the wine industry. Pasteur established first that fermentation required the presence of yeast, and second that to prevent wine from souring, it should be heated after forming to about 122 degrees Fahrenheit (50 degrees Centigrade) to kill the yeast and allow the wine to age without spoiling. Pasteurized liquids are not sterilized, that is, they are not completely free of microbes; this is why, for instance, even pasteurized milk should be kept refrigerated to retard bacterial growth.

Today, pasteurization is most often applied to milk, although it is also used for wine, fruit juice, and other liquids. The pasteurization process for milk is considered sufficiently important that it is mandated and regulated by national governmental agencies such as the Food and Drug Administration (FDA) in the United States and the Food Standards Agency in the United Kingdom. In the United States, all milk packaged for human consumption must be pasteurized if sold through interstate commerce, a regulation that has been in effect since 1987. However, private consumption of raw milk is not prohibited and some people believe it is more nutritious than pasteurized milk. The FDA does not recommend the consumption of raw milk because it may contain a variety of harmful bacteria (which would be killed by pasteurization), including Salmonella, E. coli O157:H7, Listeria, Campylobacter, and Brucella, which may cause serious illness or death. In addition, the FDA states that there are no known nutritional benefits to consuming raw, rather than pasteurized, milk. From 1998 to May 2005, the Centers for Disease Control and Prevention in the United States identified 45 outbreaks of foodborne illness traceable to unpasteurized milk or cheese made from unpasteurized milk, which produced over 1,000 illnesses, 104 hospitalizations, and 2 deaths; the actual count may be higher because many cases of foodborne illness are not reported.

Two types of pasteurization are in common use for milk. High temperature/short-time (HTST) pasteurization is more common in the United States: this involves heating milk for 30 minutes to 145 degrees Fahrenheit (63 degrees Centigrade). Ultra-high temperature (UHT) pasteurization, which is common in Europe, requires heating milk to 280 degrees Fahrenheit (138 degrees Centigrade) for two seconds. UHT milk has a shelf life of six to nine months (unlike HTST milk, which requires refrigeration) but spoils more rapidly once the container is opened.