Milk has been used for human consumption for thousands of years. Today cow's milk is one of the most popular animal milks consumed by humans. Around the world, people drink the milk of many other animals including camels, goats, llamas, reindeer, sheep and water buffalo. Milk is available in many varieties. Raw milk has not been pastuerized, and is usually available in natural food stores. Whole milk is the milk as it came from the cow and contains about 3.5% milk fat. Low-fat milk is available in two types, 2% and 1%. The 1% and 2% designations refer to the percent of fat by weight that the milk contains.. Nonfat or skim milk must by law contain less than .5% milk fat. Buttermilk was once the liquid left after butter was churned. Today, buttermilk is made commercially by adding special bacteria to nonfat or low-fat milk, giving it a slightly thickened texture and tangy flavor. Low-sodium milk has 90% of the sodium replaced by potassium. Lactose-reduced low-fat milk is a special milk with less than 30% lactose content. Ultrapasteurized milk has been heated to approximately 300F then vacuum-packed. This milk may be stored without refrigeration up to 6 months unopened. Most milk sold in the United States is pasteurized, which means the micro-organisms that cause disease (such as salmonella and hepatitis) and spoilage have been destroyed by heating, then quick-cooling the milk. Pasteurization also gives milk a longer shelf life. Most commercial milk products have also been homogenized, meaning the milk fat globules have been broken down until they are evenly and imperceptibly distributed thoughout the milk and the liquid is uniformly smooth. In Canada, whole milk means milk that has not been homogenized. There are a variety of dry and canned milk products on the market including dry milk, evaporated milk, and sweetened condensed milk. Other products made from milk include cream, butter, and cheese.
In the United States, milk containers are stamped with a sell-by date. The milk will be good for a certain amount of time after that date, providing it is kept cool (40 degF or below). At home, if the sell-by date has gone by, smelling the milk will help determine whether the milk has turned. Good milk has little or no smell, but milk that is going bad has a sour scent.