Raw Sheep Milk Near Waukesha, Wisconsin

Lactic acid bacteria acidify milk, suppress competing organisms, and build the flavor of aged cheese. Here is how all three mechanisms work and where each has limits.

Not all water in cheese is available to bacteria. Water activity rather than moisture content determines which pathogens can grow and how different cheese styles compare.

The same 60-day aging period that renders one batch of raw milk cheese safe can leave another infectious. For Salmonella, initial bacterial load is the variable that determines the outcome.

Unlike most dairy pathogens, Listeria monocytogenes thrives in the conditions that define aged cheese production. Cold tolerance, salt resistance, and biofilm formation explain why.

The lactic acid fermentation that eliminates most dairy pathogens triggers an adaptive response in E. coli O157:H7 that allows it to survive past 270 days in aged cheese.

Despite causing 1.5 million U.S. infections per year, Campylobacter rarely survives cheesemaking. Here is why oxygen, salt, and acid eliminate it reliably.