What Is Raw Milk? Ask Paul

That problem of rapid spoilage gave rise to many wonderful ways to preserve milk in various forms, by removing water, lowering its pH, and/or cooking it, all of which inhibit the microbes that cause spoilage. Necessity was the mother of the invention of cheese, yogurt, and butter, to name a few.

Going sour wasn’t the only issue with fresh milk: It could easily be infected with pathogens at the farm or in transit, and the nutrient-rich liquid makes a fantastic habitat for rapid growth of bacteria. In addition, milk's short shelf life meant that, to provide fresh milk to consumers in urban areas, dairies also had to be located in urban areas, and crowded conditions were excellent for the proliferation of pathogens. In the 19th century, milk-drinking was linked to high rates of child mortality. 

Pasteurizing milk destroys the microbes responsible for disease as well as spoilage. Today, the CDC strongly advises against consuming raw milk. Even when produced in the most sanitary conditions (which most milk is not) it can incubate germs that cause life-threatening illness.

In the 1860s, a brilliant French chemist named Louis Pasteur proved that the spoilage of milk is caused by microbes, and that heating milk to kill off the microbes made it safe to drink and  dramatically increased its shelf life.

With campaigning from public health advocates, pasteurization of milk became routine in the United States during the first half of the 20th century. 

The usual pasteurization process involves heating milk to 160°F for 15 seconds, then rapidly chilling it. Ultra-high temperature pasteurization, which gives a shelf life of months rather than weeks, brings it to 290 degrees for 2 seconds. Both methods significantly alter the flavor of the milk.

Laws vary from state to state: Some states only allow sales direct from the farmer to the consumer; others require raw milk to be labeled as not for human consumption. 

Following a series of disease outbreaks associated with unpasteurized milk, federal law made interstate sale of raw milk illegal in 1987. That law included a ban on imported cheeses made from raw milk unless they’re aged 60 days or more, since the pH of cheese decreases during aging, which kills off some (but potentially not all) pathogenic bacteria.

Lovers of raw-milk cheeses and fresh raw milk, rave about the wealth of flavor of the unpasteurized stuff. Jeffrey Steingarten writes that “it is rare—probably impossible—to find a soft, young cheese made from pasteurized milk that has the strength and complexity of flavor and the succulence of any of the raw-milk cheeses…”

Many advocates of raw milk argue that the heat of pasteurization destroys nutrients present in raw milk, but the scientific review generally concludes that pasteurization “will not substantially change the nutritional value of raw milk or other benefits associated with raw milk consumption.” (Pasteurization does kill the lactic acid bacteria responsible for souring, fermentation, and curdling, so to make yogurt and other cultured dairy products, those bacteria have to be added back to pasteurized milk.)

Interestingly, a recent analysis of retail raw milk found it contained minimal amounts of those beneficial bacteria – and that the bacteria it did contain were increasingly antibiotic-resistant.

Raw-milk proponents point out that a major reason pasteurization is necessary is because industrial farming practices (which were developed to produce milk destined to be pasteurized) are responsible for making the milk supply unsanitary, and proper conditions, as practiced on small farms, can produce raw milk with minimal risk. 

A process called microfiltration may be a promising alternative to pasteurization. It can remove bacteria from milk without heating it by passing the milk through a filter with holes less than 2 microns wide. Unpasteurized microfiltered milk is widely sold in Europe and is praised for its raw flavor but has not been approved in the U.S. due to concerns that viruses, which are generally much smaller than bacteria, can pass the filter.