The pasteurization of milk is a process of slow heating to kill bacteria and other microorganisms in order to make milk safe for human consumption. During the process many pathogenic bacteria are destroyed including Mycobacterium Tuberculosis tuberculosis, one of the most heat-tolerant pathogenic bacteria that does not form protective spores. Other bacteria, encapsulated in spores, may not be destroyed and thus pasteurized milk should still be refrigerated. During the heating process (at 143.1°F [61.7°C] for a period of at least 30 minutes) some food value of certain vitamins and proteins is lost, but the possibility of spreading bacteria with the potential of causing disease is lessened substantially.
Named for its inventor, nineteenth-century French microbiologist Louis Pasteur (1822-1895), pasteurization was originally begun as a way of keeping wine and beer from turning sour. Pasteur's research led him to believe that during the fermentation of alcoholic beverages, bacteria sometimes got into the brew and produced lactic acid which soured the valuable beer and wine. By heating the beverage at a low temperature for a given length of time, the bacteria would be destroyed. Pasteur, who theorized that bacteria and other pathogenic microorganisms were responsible for causing and spreading disease, also proposed the idea that heat sterilization of everything from food to surgical instruments would cause a drastic reduction in the transmission of bacterial disease.
A champion for the pasteurization of milk in the United States was Alice Catherine Evans (1881-1975), a bacteriologist who linked the cause of human illness to milk infected with disease-causing bacteria.
Evans was the first woman scientist ever hired by the Dairy Division of the Bureau of Animal Industry in Washington, D.C. In 1906 the Pure Food and Drug Act had been passed and part of her research was to find out how bacteria got in dairy products. Starting in 1917 she found a variety of bacteria in fresh milk and observed similarities between bacteria in this "certified" milk from the United States to disease-causing bacteria from other countries. Evans hypothesized that the bacteria came from cows rather than contamination that took place during storage and noted that people who had no contact with animals had contracted diseases. In many cases people who drank infected milk contracted brucellosis, a bacterial disease that was formerly called by a variety of names including Malta, Mediterranean, and undulant fever. (In her work with the pathogenic bacteria, Evans herself contracted the disease.) A related group of disease-causing bacteria was discovered and named for Sir David Bruce (1855-1931), a Scottish microbiologist who, with his wife Mary Steele Bruce, traced the cause of fever outbreaks in the Mediterranean to goat's milk. Even after the accumulation of much experimental evidence, many people in the dairy business were dubious of Evans's ideas. However, by the 1930s, pasteurizing milk had become a standard practice. Milk products that contain higher quantities of sugar or milkfat, are pasteurized at higher temperatures and for longer time periods since such products provide an environment more conducive to bacterial growth.
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