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.