Just about all the milk sold in the U.S. has been pasteurized and homogenized. Pasteurization refers to heating the milk to kill off any harmful bacteria, while homogenization breaks up the milk fat and mixes it in with the milk for a smoother texture and better taste.
Whole milk is the closest thing to milk fresh from the cow.
It contains about 3 percent milk fat. Low-fat milk comes in two types 2 percent milk and 1 percent milk, meaning that 9they contain 2 percent and 1 percent fat respectively. Nonfat or skim milk must contain less than percent milk fat. Buttermilk used to be the liquid left in the churn after butter was made. Now, it is made commercially, by adding cultures of bacteria to low fat milk.