Milk is a nutritive beverage obtained from various animals and consumed by humans. Most milk is obtained from dairy cows, although milk from goats, water buffalo, and reindeer is also used in various parts of the world. In the United States, and in many industrialized countries, raw cow's milk is processed before it is consumed. During processing the fat content of the milk is adjusted, various vitamins are added, and potentially harmful bacteria are killed. In addition to being consumed as a beverage, milk is also used to make butter, cream, yogurt, cheese, and a variety of other products.
The use of milk as a beverage probably began with the domestication of animals. Goats and sheep were domesticated in the area now known as Iran and Afghanistan in about 9000 B.C. , and by about 7000 B.C. cattle were being herded in what is now Turkey and parts of Africa. The method for making cheese from milk was known to the ancient Greeks and Romans, and the use of milk and milk products spread throughout Europe in the following centuries.
Cattle were first brought to the United States in the 1600s by some of the earliest colonists. Prior to the American Revolution most of the dairy products were consumed on the farm where they were produced. By about 1790, population centers such as Boston, New York, and Philadelphia had grown sufficiently to become an attractive market for larger-scale dairy operations. To meet the increased demand, farmers began importing breeds of cattle that were better suited for milk production. The first Holstein-Friesens were imported in 1795, the first Ayrshires in 1822, and the first Guernseys in 1830.
With the development of the dairy industry in the United States, a variety of machines for processing milk were also developed. In 1856, Gail Borden patented a method for making condensed milk by heating it in a partial vacuum. Not only did his method remove much of the water so the milk could be stored in a smaller volume, but it also protected the milk from germs in the air. Borden opened a condensed milk plant and cannery in Wassaic, New York, in 1861. During the Civil War, his condensed milk was used by Union troops and its popularity spread.
In 1863, Louis Pasteur of France developed a method of heating wine to kill the microorganisms that cause wine to turn into vinegar. Later, this method of killing harmful bacteria was adapted to a number of food products and became known as pasteurization. The first milk processing plant in the United States to install pasteurizing equipment was the Sheffield Farms Dairy in Bloomfield, New Jersey, which imported a German-made pasteurizer in 1891. Many dairy operators opposed pasteurization as an unnecessary expense, and it wasn't until 1908 that Chicago became the first major city to require pasteurized milk. New York and Philadelphia followed in 1914, and by 1917 most major cities had enacted laws requiring that all milk be pasteurized.
One of the first glass milk bottles was patented in 1884 by Dr. Henry Thatcher, after seeing a milkman making deliveries from an open bucket into which a child's filthy rag doll had accidentally fallen. By 1889, his Thatcher's Common Sense Milk Jar had become an industry standard. It was sealed with a waxed paper disc that was pressed into a groove inside the bottle's neck. The milk bottle, and the regular morning arrival of the milkman, remained a part of American life until the 1950s, when waxed paper cartons of milk began appearing in markets.
In 1990, the annual production of milk in the United States was about 148 billion lb (67.5 billion kg). This is equivalent to about 17.2 billion U.S. gallons (65.1 billion liters). About 37% of this was consumed as fluid milk and cream, about 32% was converted into various cheeses, about 17% was made into butter, and about 8% was used to make ice cream and other frozen desserts. The remainder was sold as dry milk, canned milk, and other milk products.
There are many different types of milk. Some depend on the amount of milk fat present in the finished product. Others depend on the type of processing involved. Still others depend on the type of dairy cow that produced the milk.
The federal Food and Drug Administration (FDA) establishes standards for different types of milk and milk products. Some states use these standards, while others have their own standards. Prior to 1998, the federal standards required that fluid milk sold as whole milk must have no less than 3.25% milk fat, low-fat milk must have 0.5-2.0% milk fat, and skim milk must have less than 0.5% milk fat. Starting in 1998, the FDA required that milk with 2% milk fat must be labeled as "reduced-fat" because it did not meet the new definition of low-fat products as having less than 3 grams of fat per serving. Milk with 1% milk fat could still be labeled as "low-fat" because it did meet the definition. As a comparison, light cream has no less than 18% milk fat, and heavy cream has no less than 36% milk fat.
Other types of milk are based on the type of processing involved. Pasteurized milk has been heated to kill any potentially harmful bacteria. Homogenized milk has had the milk fat particles reduced in size and uniformly blended to prevent them from rising to the top in the form of cream. Vitaminfortified milks have various vitamins added. Most milk sold in markets in the United States is pasteurized, homogenized, and vitamin-fortified.
Grade A milk refers to milk produced under sufficiently sanitary conditions to permit its use as fluid milk. About 90% of the milk produced in the United States is Grade A milk. Grade B milk is produced under conditions that make it acceptable only for manufactured products such as certain cheeses, where it undergoes further processing. Certified milk is produced under exceedingly high sanitary standards and is sold at a higher price than Grade A milk.
Specialty milks include flavored milk, such as chocolate milk, which has had a flavoring syrup added. Other specialty milks include Golden Guernsey milk, which is produced by purebred Guernsey cows, and All-Jersey milk, which is produced by registered Jersey cows. Both command a premium price because of their higher milk fat content and creamier taste.
Concentrated milk products have varying degrees of water removed from fluid milk. They include, in descending order of water content, evaporated milk, condensed milk, and dry milk.
The average composition of cow's milk is 87.2% water, 3.7% milk fat, 3.5% protein, 4.9% lactose, and 0.7% ash. This composition varies from cow to cow and breed to breed. For example, Jersey cows have an average of 85.6% water and 5.15% milk fat. These figures also vary by the season of the year, the animal feed content, and many other factors.
Vitamin D concentrate may be added to milk in the amount of 400 international units (IU) per quart. Most low fat and skim milk also has 2,000 IU of Vitamin A added.
Milk is a perishable commodity. For this reason, it is usually processed locally within
The federal Food and Drug Administration (FDA) publishes the Grade A Milk Ordinance which sets sanitation standards for milk production in most states and for all interstate milk shippers. The composition of milk and milk products is specified in Agricultural Handbook 52 published by the United States Department of Agriculture. It lists both federal and state standards. Testing of milk products includes tests for fat content, total solids, pasteurization efficiency, presence of antibiotics used to control cow disease, and many others.
The trend to low-fat dairy products over the last 20 years is expected to continue in the future. Sales of butter are expected to decline, while sales of low-fat yogurt and low-or reduced-fat milk are expected to increase. Overall consumption of liquid milk is expected to increase as the population increases.
Giblin, James. Milk: The Fight for Purity. Thomas Y. Crowell, 1986.
Hui, Y.H., ed. Encyclopedia of Food Science and Technology. John Wiley and Sons Inc., 1992.
Kroschwitz, Jacqueline I. and Mary Howe-Grant, ed. Encyclopedia of Chemical Technology, 4th edition. John Wiley and Sons Inc., 1993.
McGraw-Hill Encyclopedia of Science and Technology, McGraw-Hill, 1997.
Dairy Farmers of Ontario. http://www.milk.org .
International Dairy Foods Association. http://www.idfa.org .
National Milk Producers Federation. http://nmpf.org .
— Chris Cavette