Dictionary:

milk

  (mĭlk)

1. A whitish liquid containing proteins, fats, lactose, and various vitamins and minerals that is produced by the mammary glands of all mature female mammals after they have given birth and serves as nourishment for their young.
2. The milk of cows, goats, or other animals, used as food by humans.
3. A liquid, such as coconut milk, milkweed sap, plant latex, or various medical emulsions, that is similar to milk in appearance.

1. 1. To draw milk from the teat or udder of (a female mammal).
   2. To draw or extract a liquid from: milked the stem for its last drops of sap.
2. To press out, drain off, or remove by or as if by milking: milk venom from a snake.
3. Informal.
   1. To draw out or extract something from, as if by milking: milked the witness for information.
   2. To obtain money or benefits from, in order to achieve personal gain; exploit: “The dictator and his cronies had milked their country of somewhere between $5 billion and $10 billion” (Russell Watson).

1. To yield or supply milk.
2. To draw milk from a female mammal.

[Middle English, from Old English milc.]

Background

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.

History

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.

Types of Milk

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.

Raw Materials

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.

The Manufacturing
Process

Milk is a perishable commodity. For this reason, it is usually processed locally within a few hours of being collected. In the United States, there are several hundred thousand dairy farms and several thousand milk processing plants. Some plants produce only fluid milk, while others also produce butter, cheese, and other milk products.

Collecting

• Dairy cows are milked twice a day using mechanical vacuum milking machines. The raw milk flows through stainless steel or glass pipes to a refrigerated bulk milk tank where it is cooled to about 40° F (4.4° C).
• A refrigerated bulk tank truck makes collections from dairy farms in the area within a few hours. Before pumping the milk from each farm's tank, the driver collects a sample and checks the flavor and temperature and records the volume.
• At the milk processing plant, the milk in the truck is weighed and is pumped into refrigerated tanks in the plant through flexible stainless steel or plastic hoses.

Separating

• The cold raw milk passes through either a clarifier or a separator, which spins the milk through a series of conical disks inside an enclosure. A clarifier removes debris, some bacteria, and any sediment that may be present in the raw milk. A separator performs the same task, but also separates the heavier milk fat from the lighter milk to produce both cream and skim milk. Some processing plants use a standardizer-clarifier, which regulates the amount of milk fat content in the milk by removing only the excess fat. The excess milk fat is drawn off and processed into cream or butter.

Fortifying

• Vitamins A and D may be added to the milk at this time by a peristaltic pump, which automatically dispenses the correct amount of vitamin concentrate into the flow of milk.

Pasteurizing

• The milk—either whole milk, skim milk, or standardized milk—is piped into a pasteurizer to kill any bacteria. There are several methods used to pasteurize milk. The most common is called the high-temperature, short-time (HTST) process in which the milk is heated as it flows through the pasteurizer continuously. Whole milk, skim milk, and standardized milk must be heated to 161° F (72° C) for 15 seconds. Other milk products have different time and temperature requirements. The hot milk passes through a long pipe whose length and diameter are sized so that it takes the liquid exactly 15 seconds to pass from one end to the other. A temperature sensor at the end of the pipe diverts the milk back to the inlet for reprocessing if the temperature has fallen below the required standard.

Homogen izing

• Most milk is homogenized to reduce the size of the remaining milk fat particles. This prevents the milk fat from separating and floating to the surface as cream. It also ensures that the milk fat will be evenly distributed through the milk. The hot milk from the pasteurizer is pressurized to 2,500-3,000 psi (17,200-20,700 kPa) by a multiple-cylinder piston pump and is forced through very small passages in an adjustable valve. The shearing effect of being forced through the tiny openings breaks down the fat particles into the proper size.
• The milk is then quickly cooled to 40° F (4.4° C) to avoid harming its taste.

Packaging

• The milk is pumped into coated paper cartons or plastic bottles and is sealed. In the United States most milk destined for retail sale in grocery stores is packaged in one-gallon (3.8-liter) plastic bottles. The bottles or cartons are stamped with a "sell by" date to ensure that the retailers do not allow the milk to stay on their shelves longer than it can be safely stored.
• The milk cartons or bottles are placed in protective shipping containers and kept refrigerated. They are shipped to distribution warehouses in refrigerated trailers and then on to the individual markets, where they are kept in refrigerated display cases.

Cleaning

• To ensure sanitary conditions, the inner surfaces of the process equipment and piping system are cleaned once a day. Almost all the equipment and piping used in the processing plant and on the farm are made from stainless steel. Highly automated clean-in-place systems are incorporated into this equipment that allows solvents to be run through the system and then flushed clean. This is done at a time between the normal influx of milk from the farms.

Quality Control

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 Future

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.

Where to Learn More

Books

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.

Other

Dairy Farmers of Ontario. http://www.milk.org.

International Dairy Foods Association. http://www.idfa.org.

National Milk Producers Federation. http://nmpf.org.

[Article by: Chris Cavette]

The lacteal secretion, practically free from colostrum, obtained by the complete milking of one or more healthy cows and containing not less than 8.25% milk solids (not fat) and not less than 3.25% milk fat. Among mammals, humans utilize milk as a source of food. The dairy cow supplies the vast majority of milk for human consumption, particularly in the United States; however, milk from goats, water buffalo, and reindeer is also consumed in other countries. Without qualification, the general term milk refers to cow's milk.

Average composition of milk is 87.2% water, 3.7% fat, 3.5% protein, 4.9% lactose, and 0.7% ash. Whole milk and skim milk are classified as excellent sources of calcium, phosphorus, and riboflavin because 10% of the daily nutritional requirement is supplied by not over 100 kcal (420 kilojoules). These two beverages are also classified as good sources of protein and thiamine; and whole milk is a good source of vitamin A. To be classified as good, the source must contribute 10% of a nutrient in not over 200 kcal (840 kilojoules). Milk is a good source of protein rich in all the essential amino acids.

Processing

Most raw milk collected at farms is pumped from calibrated and refrigerated stainless steel tanks into tank trucks for delivery to processing plants. The actual processing of raw milk begins with either separation or clarification. These machines are essentially similar except that in the clarifier the cream and skim milk fractions are not separated. Many processers have units called standardizer-clarifiers which separate only a small fraction of the fat from the raw whole milk; the amount of fat removed can be regulated. This facilitates the production of milk of standard fat content even though that in the raw product may vary.

Milk is rendered free of pathogenic bacteria by pasteurization. This is accomplished in a manner so that every particle of milk is heated to a specified temperature and held at that temperature for a specified time. See also Pasteurization.

Fat globules in fluid milk products are broken by homoge-nization into sizes that are 2 micrometers or less and thus are relatively unaffected by gravitational forces. The U.S. Public Health Service specifies that the fat content of the upper 6 in. (100 m]) of a quart of homogenized milk that has been undisturbed for 48 h cannot differ by more than 10% from that of the remainder.

Most milk is fortified with 400 international units (IU) of vitamin D per quart, and some skim milk is fortified also with 2000 IU of vitamin A per quart. These vitamins as concentrates are added either by automatic dispensing into a continuous flow of milk prior to pasteurization or as a single quantity in a batch operation.

Products

Many fermented or cultured products are produced from milk. These fermentations require the use of bacteria that ferment lactose or milk sugar.

Cultured buttermilk consists of skim milk or low-fat milk which is pasteurized at 180°F (82°C) for 30 min, cooled to 72°F (22°C), and inoculated with an active starter culture containing Streptococcus lactis and Leuconostoc citrovorum. The mixture is incubated at 70°F (21°C) and cooled when acidity is developed to approximately 0.8%. This viscous product is then agitated, packaged, and cooled. The desired flavor is created by volatile acids and diacetyl; the latter is produced by L. citrovorum.

One of the oldest fermented milks known is yogurt. Yogurt is prepared using whole or low-fat milk with added nonfat milk solids. The milk is heated to approximately 180°F (82°C) for 30 min, homogenized, cooled to 115°F (46°C), inoculated with an active culture, and packaged. Yogurt cultures are mixtures of Streptococcus thermophilus and Lactobacillus bulgaricus in a 1:1 ratio. Balance of these organisms in the culture is important for production of a quality product.

Concentrated and dried milk products

To reduce costs of transportation and handling, either part or all of the water is removed from milk. Moreover, the partly dehydrated milk can either be sterilized or dried to permit unrefrigerated storage for prolonged periods. Many different milk products (such as dry whole milk, evaporated milk, and condensed milk) are produced for these specific reasons. The composition of some of these is controlled by standards of identity and some by request of the commercial buyer.

The secretion of the mammary gland of mammals. A 300-mL portion of cow's milk is a rich source of vitamins B₂, B₁₂, calcium, and iodine; a source of protein, vitamin A, and vitamin B₁; full cream milk contains 11.4 g of fat of which 63% is saturated; supplies 200 kcal (840 kJ); skimmed milk contains 0.3 g of fat; supplies 100 kcal (420 kJ); Channel Islands milk contains 14.4 g of fat of which 68% is saturated; supplies 230 kcal (970 kJ).

Ordinary milk contains 3.9% fat; Channel Islands milk, 5.1%; sheep's milk, 6.0%, buffalo milk, 7.5%; human milk contains 4.1% fat.

A 280-mL portion of goat's milk is a rich source of vitamin B₁₂ and calcium; a good source of vitamin B₂; a source of protein, vitamin A, zinc, and copper; contains 13.5 g of fat of which 51% is saturated; supplies 215 kcal (900 kJ).

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 natural 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 31⁄2 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 soymilk as well as listings for milk's most widely distributed by-products: butter; cheese; cream; sour cream; yogurt.

Idioms beginning with milk:
milk of human kindness, the

In addition to the idiom beginning with milk, also see cry over spilt milk.

Definition: tap; exploit
Antonyms: hoard, save

For more information on milk, visit Britannica.com.

The care of cows, milking, and butter-making were surrounded by multiple magical precautions and fears, presumably because they were subject to difficulties which were poorly understood. Various diseases could cause cows to yield bloody milk, or none, and poor-quality milk or poor hygiene in the dairy could make churning futile, but these failures were often blamed upon witchcraft. To guard against this, protective charms and plants were placed in or beside cattle-sheds, the cows were blessed and wassailed, and if need be countercharms would be used. An alternative explanation for bloody milk was that it was a punishment for the wickedness of stealing a robin's or swallow's eggs.

Cattle diseases might also be blamed on witches, as is seen from accounts of counterspells involving hearts and pins or burning one of the dead beasts. Whenever a cow miscarried, the custom in Yorkshire was to dig a deep hole under the threshold of the byre and bury the dead calf there, feet up; this would prevent further trouble for many years, but would eventually have to be repeated (Atkinson, 1891: 62).

Dairy work also had its problems, for which magical remedies are reported from many districts. As milk sours easily in thundery weather, it was wise to put thunderstones on the windowsill, and plant bay, elder, or holly nearby. Witches might steal the goodness of the milk by spells, making it impossible to churn it into butter; the standard countercharm was to plunge a red-hot poker into the churn. The dairy could of course be protected by a horseshoe or hagstone, by a rowan growing nearby; there was also a verbal charm to be recited while churning:

Come, butter, come!
Come, butter, come!
Peter stands at the gate,
Waiting for a buttered cake.
Come, butter, come!

The procedure of extracting the milk from the udder usually with a milking machine. The process and the machine play a large part in the transmission of mastitis, pseudocowpox, bovine ulcerative mammillitis, cowpox, udder impetigo, teat papillomatosis, and in the causation of black spot. It is a special portal of entry for infection in the cow, goat and rarely sheep.

• m. bail — the head lock or stock which restrains the cow while she is milked.
• m. hygiene — includes milking machine sanitation between milkings, teat cup sanitation during milking, teat washing, teat dipping or spraying, hand disinfection, fly control, shed floor washing.
• m. machine — see milking machine.
• m. order — the order in which groups of cattle in a milking herd pass through the milking parlor twice each day; for reasons of mastitis control the order should be heifers first followed by uninfected senior cows, followed by known infected but clinically normal individuals and then cows with clinical mastitis last.
• m. parlor — the room or shed used for milking cows. The milking stalls may be in line abreast (a walkthrough), angled away from a central pit, and often not divided into stalls (herringbone), in-line behind each other on either side of a pit (tandem), or on a milking platform that rotates around a central point (carousel or rotary); there are a number of other variations on these styles.
• m. ratio — the duration of the milk flow within each pulsation cycle expressed as a percentage of the period when milk does not flow.
• m. time — 1. the time of day at which milking occurs.
— 2. total time taken to milk the entire herd or the average time taken to milk each cow.

Tutor's tip: Of all the "milch" (giving milk) cows, Mary was the easiest to "milk" (to draw milk from a cow).