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Posted by on May 12, 2017 in Tell Me Why Numerous Questions and Answers |

How Is Milk Pasteurized?

How Is Milk Pasteurized?

Milk is pasteurized by heating it to a temperature of about 62°Celsius (about 143°Fahrenheit) and then maintaining that temperature for about half an hour. The treatment kills most of the bacteria which cause milk to go sour quickly or may produce disease in human beings. This temperature is chosen because it is the lowest temperature that will kill the micro bacterium tuberculosis, the carrier of tuberculosis which used to kill people of all ages.

At the same time it is low enough not to alter the taste too much. Pasteurized milk is therefore much safer than untreated milk, especially for babies, and in many countries is the only milk allowed to be sold. The process is named after the French scientist Louis Pasteur (1822—1895) whose discoveries revolutionized knowledge about the effects of bacteria.



Milk is an excellent medium for microbial growth, and when stored at ambient temperature bacteria and other pathogens soon proliferate. The US Centers for Disease Control (CDC) says improperly handled raw milk is responsible for nearly three times more hospitalizations than any other food-borne disease source, making it one of the world’s most dangerous food products. Diseases prevented by pasteurization can include tuberculosis, brucellosis, diphtheria, scarlet fever, and Q-fever; it also kills the harmful bacteria Salmonella, Listeria, Yersinia, Campylobacter, Staphylococcus aureus, and Escherichia coli, among others.

pasteurized milk packaging


Before the widespread urban growth caused by industrialization, people kept dairy cows even in urban areas and the short time period between production and consumption minimized the disease risk of drinking raw milk. As urban densities increased and supply chains lengthened to the distance from country to city, raw milk (often days old) became recognized as a source of disease. For example, between 1912 and 1937 some 65,000 people died of tuberculosis contracted from consuming milk in England and Wales alone. In the early 1900s, in Arizona, Jane H. Rider “publicized the link between infant mortality and contaminated milk, and finally convinced the dairy industry to pasteurize milk.”

Developed countries adopted milk pasteurization to prevent such disease and loss of life, and as a result milk is now widely considered one of the safest foods. A traditional form of pasteurization by scalding and straining of cream to increase the keeping qualities of butter was practiced in Great Britain before 1773 and was introduced to Boston in the British Colonies by 1773, although it was not widely practiced in the United States for the next 20 years. It was still being referred to as a “new” process in American newspapers as late as 1802.

Pasteurization of milk was suggested by Franz von Soxhlet in 1886. In the early 20th century, Milton Joseph Rosenau established the standards (i.e. low temperature, slow heating at 60 °C (140 °F) for 20 minutes) for the pasteurization of milk while at the United States Marine Hospital Service, notably in his publication of The Milk Question (1912). States in the U.S.A. began enacting mandatory dairy pasteurization laws with the first in 1947, and in 1973 the U.S. Federal Government required pasteurization of milk used in any interstate commerce.


  • ESL milk has a microbial filtration step and lower temperatures than UHT milk. Since 2007, it is no longer a legal requirement in European countries (for example in Germany) to declare ESL milk as ultra-heated; consequently, it is now often labeled as “fresh milk” and just advertised as having an “extended shelf life,” making it increasingly difficult to distinguish ESL milk from traditionally pasteurized fresh milk.






Content for this question contributed by Kathy Willenburg, resident of Florence, Boone County, Kentucky, USA