A much-publicized and ongoing debate regarding both the food safety and flavor of cheese made using either raw (unpasteurized) milk or pasteurized milk is currently underway. The law in the U.S. dictates that raw-milk cheeses cannot be sold or consumed if they are younger than sixty days old, regardless of whether they are produced domestically or imported. Cheeses made from milk that is pasteurized can be consumed at any age.
Raw milk, as the name suggests, is unheated and therefore contains natural bacteria and microflora that give the milk flavor and character, which are then translated into the cheese; pasteurized milk is heated and then cooled. Experienced cheesemakers using milk from a known source (usually their own animals or those from a local farm) can safely make cheese from raw milk. Larger factories, however, buy milk from many sources, which is usually consolidated in a milk truck prior to processing, so pasteurization is necessary to ensure consistency. In general, cheeses made from raw milk have a greater depth of flavor, but it is possible to make a wonderful cheese from pasteurized milk–it all depends on the quality of the milk and the skill of the cheesemaker.
The sixty-day rule was created with consideration for the lactic acid that forms naturally as the cheese matures; after sixty days, acidity within the cheese is generally acknowledged to have reached a level that is inhospitable to any harmful pathogens, thereby making it safe to eat.