Milk has been used for human consumption for thousands and thousands of years, as proven by cave drawings showing cows being milked. Today cow's milk is still one of the most popular (especially in the United States) animal milks consumed by humans. Around the world, people drink the milk from many other animals including camels, goats, llamas, reindeer, sheep and water buffalo. Most milk packs a nutritional punch and contains protein, calcium, phosphorus, vitamins A and D, lactose (milk sugar) and riboflavin. On the minus side, milk's natural sodium content is quite high. Most milk sold in the United States today is pasteurized, which means the microorganisms that cause diseases (such as salmonella and hepatitis) and spoilage have been destroyed by heating, then quick-cooling, the milk. Pasteurization eliminates the possibility of disease and gives milk a longer shelf life. Most commercial milk products have also been homogenized, meaning that the milk fat globules have been broken down mechanically until they are evenly and imperceptibly distributed throughout the milk. The end result is that the cream does not separate from the milk and the liquid is uniformly smooth. In 1993, the Federal Drug Administration approved supplementing dairy cows with a genetically produced hormone protein known as bovine somatotropin (bst). bst is a naturally occurring growth hormone that's found in all cows. When bioengineered bst is injected into dairy cows, their milk production increases by up to 25 percent. Scientists assert that the composition of milk from bst-injected cows is not altered in any way and has no biological effect on humans, although many opponents are not convinced. There is no mandatory labeling for milk from bst-supplemented cows. However, in some smaller market areas, you may find dairy products voluntarily labeled as "farmer certified to not come from bst-supplemented cows. " Milk is available in many varieties. Raw milk, usually only commercially available in health-food stores, has not been pasteurized. Advocates say it's better nutritionally because vitamins and natural enzymes have not been destroyed by heat. The dairies that are certified to sell raw milk have rigid hygiene standards and their herds are inspected regularly. But the milk is still not pasteurized and therefore carries some potential risk of disease. Almost all other pasteurized and homogenized milks are fortified with vitamins A and D. Whole milk is the milk just as it came from the cow and contains about 3 1/2 percent milk fat. Lowfat milk comes in two basic types: 2 percent, meaning 98 percent of the fat has been removed; and 1 percent, which is 99 percent fat-free. A few lowfat milks contain only 1/2 percent milk fat but they're not widely available. Nonfat or skim milk must by law contain less than 1/2 percent milk fat. Both lowfat and nonfat milk are available with milk solids added, in which case the label states "Protein-fortified. " Not only does this boost the protein to 10 grams per cup, but it also adds body and richness. Federal law requires that both lowfat and nonfat milk be fortified with 2,000 International Units (iu) of vitamin A per quart. Though vitamin D fortification is optional, 400 iu per quart is usually also added. Buttermilk of times past was the liquid left after butter was churned. Today it is made commercially by adding special bacteria to nonfat or lowfat milk, giving it a slightly thickened texture and tangy flavor. Some manufacturers add flecks of butter to give it an authentic look. Dry or powdered buttermilk is also available (see dry milk). Sweet acidophilus milk (whole, lowfat or nonfat) has had friendly and healthful lactobacillus acidophilus bacteria added to it. It tastes and looks just like regular milk but many scientists believe it has an advantage because the acidophilus culture restores nature's balance to the digestive tract. Low-sodium milk, in which 90 percent of the sodium is replaced by potassium, is a special product available in limited supply for those on sodium-restricted diets. Lactose-reduced lowfat milk is for people suffering from lactose intolerance. The lactose content in this special lowfat milk has been reduced to only 30 percent. Ultrapasteurized milk has been quickly heated to about 300°F, then vacuum-packed. It may be stored without refrigeration for up to 6 months until opened, after which it must be refrigerated. Though the high heat destroys spoilage-causing microorganisms, it also gives a "cooked" flavor to the milk. Chocolate milk is whole milk with sugar and chocolate added to it. Chocolate dairy drink (sometimes labeled simply chocolate drink) is skim milk with the same flavorings added. In either case, if cocoa is used instead of chocolate, the product is labeled "chocolate-flavored drink. " There are a variety of dry milk and canned milk products on the market. (See dry milk, evaporated milk and sweetened condensed milk). Buying milk: Always check the date on the carton to make sure the milk you're buying is the freshest available. Pull dates (see open dating) are intentionally conservative, and most milk in a market with rapid turnover will keep at least a week after purchase. Storing milk: Refrigerate milk as soon as you get it home from the store. Milk readily absorbs flavors so always close milk cartons or other containers tightly. The storage life of milk is reduced greatly when allowed to sit out at room temperature for 30 minutes or more, as it would if put in a pitcher for serving. Rather than returning such milk to its original carton, cover the pitcher with plastic wrap, refrigerate and use that milk within 2 days. See also soy milk, as well as listings for milk's most widely distributed by-products: butter; cheese; cream; sour cream; yogurt.