The process of heating milk to kill pathogens and prevent spoilage was developed back in the 1860's, but it didn't become standard until dairy farming became industrialized in the 1900's. As milk started being collected and distributed by centralized companies, the risk of contamination grew and pasteurization became a necessity.
There are actually three different methods of pasteurization:
1. The milk is heated to 145-degrees Fahrenheit for 30-35 minutes. This is called "batch" pasteurization and is employed when working with a relatively small amount of milk (up to a few hundred gallons). This has a minimal affect on the milk's flavor and is the method most often used for small-scale cheese production.
2. Larger industrial operations use the "high temperature, short time" (HTST) method, which involves pumping milk through a heat exchanger at a minimum of 162-degrees Fahrenheit for 15 seconds. This significantly alters the flavor of the milk, producing a cooked flavor as compared to raw or batch-pasteurized milk. The majority of milk bought at a commercial grocery store will be HTST pasteurized.
3. Finally, milk can be "ultra-high temperature" (UHT) pasteurized. UHT milk is heated to between 265- and 300-degrees Fahrenheit for 1-3 seconds. This milk has a noticeable cooked flavor - even to our modern palates - and can be stored unrefrigerated for several months.
It's unclear exactly what side-effects pasteurization has on the nutritional value of milk. While it's good that harmful pathogens are destroyed through pasteurization, it's also possible that beneficial enzymes and proteins are being destroyed in the process. Many folks believe that the nutritional benefit of raw milk outweighs any risk from drinking it unpasteurized.
As we mentioned last week, homogenization and pasteurization aren't necessarily two sides of the same coin. The problem is that without pasteurization, active enzymes in homogenized milk will attack the fat globules, which are made unprotected during the homogenization process. This produces off-flavors and rancidity. Therefore, homogenized milk needs to be pasteurized, but milk can be pasteurized without being homogenized.
Raw milk or pasteurized - where do you stand?