Whole, 2%, 1%, SkimWhole milk hasn’t had any of its naturally occurring 3.5% fat removed. Two-percent milk has had enough of the fat removed to bring it down to, obviously, 2% and 1% milk is 1% fat. Both 2% milk and 1% milk are often labeled “low fat.” Skim milk has had all the fat removed and is sometimes labeled “fat free” or “nonfat.”
Most milk sold in the U.S. is homogenized. Left on its own, the fat in milk will naturally separate (hence the phrase “cream rises to the top”). Homogenization uses high pressure to emulsify milk into a stable product. Unhomogenized milk, by contrast, will almost always have a layer of cream on the top. It is usually available only from small, local dairies and is often sold in old-fashioned glass bottles.
Some homogenization processes use more pressure than others and use the label "ultra-homogenized." The higher pressure extends the life of the milk and can be worth seeking out for people who use milk sparingly.
Pasteurized milk has been heated to 161°F for 15 to 30 seconds to kill bacteria and other germs and then quickly cooled and packaged. The vast majority of milk sold in the U.S. has been pasteurized.
Ultra-pasteurized milk or ultra-high temperature (UTH) pasteurized milk has been very quickly brought to 250°F and then just as quickly cooled. This high-temperature treatment extends the shelf-life of the milk (several months instead of a few weeks for regular pasteurized milk). UTH is the method used for milk that is packaged in antiseptic, room-temperature-stable containers. People not used to it often find UTH milk tastes “cooked” or “off.”
rBST-FreeBovine somatotropin (BST) is a hormone found in all cows and all cow milk. Cows with higher levels of BST produce more milk, so some dairies inject cows with a synthetic form of the hormone recombinant bovine somatotropin (rBST). The USDA has stated that milk from rBST-treated cows is identical to that of rBST-free cows. Critics object to the use of synthetic hormones in the food supply and cite the fact that several nations have banned the use of rBST. "Artificial hormone free" or "synthetic hormone free" labels are another way of saying that the milk is rBST-free.
Milk labeled as certified organic comes from cows that 1) have been fed certified organic feed and 2) haven’t been treated with antibiotics or synthetic hormones. Certified organic feed is grown under several regulations: Prohibition of synthetic chemicals, irradiation, sewage sludge, or genetically modified organisms; grown on land that has been free from all of the above for three years; from farms that keep detailed records of practices used and that are subject to periodic on-site inspections. Learn more About Organic here.
Note that because certified organic milk comes from cows that haven’t been given synthetic hormones, it is also rBST-free.