What is the difference between raw and pasteurized milk and how do these differences translate into cheese?
Raw milk comes straight from the animal and, rather than being subjected to heat treatment, is simply filtered and cooled before use. Raw milk has a higher vitamin content than heat-treated milk and allows for a fullness and depth of flavor that is lost when the milk is pasteurized.
The pasteurization process (invented by Louis Pasteur, above), in which milk is heated to a specific temperature for a specific length of time, is intended to kill off potentially dangerous bacteria that can contaminate milk. However, it also kills some benign bacteria that can be useful in the cheese-making process. Most cheese makers prefer to work with raw milk, as it brings out the subtleties of the pasturing process and the end result more accurately represents the diet of the animals.
The U.S. Food and Drug Administration requires that any cheese made from raw milk must be aged for a minimum of 60 days at a temperature above 35 degrees Fahrenheit. Since the 1950s, it has also banned the import of raw milk cheeses aged less than 60 days. After this date, the potentially harmful bacteria are thought to have died off.
Traditionally, all cheeses were made with raw milk straight from small herds whose health was relatively easy to monitor. Many regulations on European cheese production actually prohibit the use of pasteurized milk. To meet controlled designation of origin standards, cheeses like Comté, Gruyère and Parmesan must be made with raw milk.
Pasteurization actually inactivates many of the milk's own enzymes and kills off useful bacteria, therefore requiring the addition of bacterial agents. Ultimately, pasteurization is not a guarantee of safety. In recent years, outbreaks of salmonella and other food-borne diseases have occurred in pasteurized milk, thanks to unclean conditions at dairy processing plants.
What pasteurization often does is lead to a train of thought that sanitary conditions are less important if the milk is heat-treated.