Raw Milk in Philadelphia, Pennsylvania

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.

Raw milk cheese sold across state lines in the U.S. must be aged 60 days by federal law. Here is where that requirement came from and what it was designed to prevent.