What is raw milk cheese vs. pasteurized cheese vs. thermalized cheese?

Pasteurization was invented by Louis Pasteur in the middle of the 19th century. It describes the process of heating liquids in order to reduce the levels of viruses, bacteria, molds, yeasts, and protozoa present in the liquid. Milk is a very friendly environment for the growth of micro-organisms (it's loaded with lactose, or milk sugar), and pasteurization has historically made milk (and dairy in general) much safer. However there are also micro-organisms living in milk that are beneficial to human health and also to the process of cheesemaking, and these are also decimated by pasteurization.

There are several methods of pasteurization, all of which have different effects on the milk especially with regards to cheesemaking. HTST (high temperature, short time) pasteurization calls for heating the milk to 71.7 °C/161 °F for 15-20 seconds. UHT (ultra high temperature) pasteurization calls for heating the milk to 138 °C/250 °F for a split second. Such a high temperature actually cooks the milk and renders it unsuitable for cheesemaking. It is a widely used technique, however, since it drastically extends the shelf of the milk.

Raw milk cheese is made without pasteurizing the milk first, the way that cheese had been made for thousands of years until the 19th century. Proponents of raw milk cheese argue that the beneficial micro-organisms in the milk contribute unique flavors to the cheese, while the cheesemaking process itself serves to limit the number of harmful micro-organisms if done under sanitary conditions. Since the 1940s the U.S. has banned all raw milk cheeses aged fewer than 60 days, since it is thought that any micro-organisms living in the cheese would not be able to survive past that.

There is a third type of milk treatment, thermalization, which involves heating the milk only to 60-65 °C/140-150 °F for 15 to 30 seconds then chilling before re-heating at the start of cheesemaking. This process reduces the number of micro-organisms, but not so much so that the resulting cheese will be without flavor. The United States FDA considers this still to be raw milk, while the European Union considered it pasteurized.