A pasteurization primer explains why processed milk is safe to drink even amid avian flu outbreaks in dairy cow herds

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The outbreak of H5N1 avian flu has now infected cows, sparking widespread concern about the safety of consuming cow milk. Dairy expert Kerry E. Kaylegian explains pasteurization and how it plays a crucial role in preventing foodborne illness, including avian flu, for The Conversation, an academic journalistic platform.

What can make milk unsafe? Like many animal foods, dairy products come with "numerous opportunities for contamination by pathogens that cause illness and organisms that make food spoil," Kaylegian writes. "Our milk comes from animals that graze outdoors and live in barns. Milk is picked up from the farm in tanker trucks and delivered to the processing plant. . . . Listeria monocytogenes comes from environmental sources like soil and water. . . . Other pathogens commonly associated with dairy animals and raw milk include E. coli, Campylobacter, the most common cause of diarrheal illness in the U.S.; and Salmonella."

How does heat make dairy safer to consume? "Pasteurization heats every particle of a food to a specific temperature for a continuous length of time to kill the most heat-resistant pathogen associated with that product," Kaylegian explains. 

How is dairy pasteurized? Milk processors can choose between pasteurization methods, such as vat or  high-temperature short-time pasteurization, which can process large quantities of milk. However, the end result is the same: pathogen-free milk. Kalegian writes, "Processors may treat milk beyond minimum times or temperatures to provide an extra margin of safety or to reduce bacteria that can cause milk to spoil, thus increasing the product's shelf life."

How does avian flu in cows change how dairy products are handled? The processes are the same, and once milk is pasteurized, it is considered safe. Kaylegian adds, "Research so far has shown that virus particles end up in the milk of infected cows but that pasteurization will inactivate the virus. The Food and Drug Administration is advising consumers not to drink raw milk because there is limited information about whether it may transmit avian flu. . . . The agency also urges producers not to manufacture or sell raw milk or raw milk products, including cheese, made from milk from cows showing symptoms of illness." 

Kerry E. Kaylegian is an extension food scientist in Pennsylvania. As part of her work, she provides technical support to milk processors working to produce high-quality, safe dairy foods. 

To watch a video on pasteurization, click here.