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A glass of cow's milk.
Milk is an opaque white liquid produced by the mammary glands of female mammals (including monotremes). Mammary glands are highly specialized sweat glands. The female ability to produce milk is one of the defining characteristics of mammals. It provides the primary source of nutrition for newborns before they are able to digest other types of food. The early lactation milk is known as colostrum, and carries the mother's antibodies to the baby. It can reduce the risk of many diseases in the baby. Males of all mammal species retain the breasts that are part of the fundamental mammalian animal structure, hence their nipples. Lactation occurs in males in certain rare circumstances, both naturally and artificially, however, some pharmaceuticals precipitate lactation in males readily. The exact components of raw milk varies by species, but it contains significant amounts of saturated fat, protein and calcium as well as vitamin C.

Types of milk consumption

There are two distinct types of milk consumption: a natural source of nutrition for all infant mammals; and a food product for humans of all ages derived from other animals.

Nutrition for infant mammals

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A goat kid feeding on its mother's milk.
In almost all mammals, milk is fed to infants through breastfeeding, either directly or, for humans, by expressing the milk to be stored and consumed later. Some cultures, historically or presently, continue to use breast milk to feed their children until as old as seven years.[1]

Food product for humans

In many cultures of the world, especially the Western world, humans continue to consume milk beyond infancy, using the milk of other animals (in particular, cows) as a food product. For millennia, cow's milk has been processed into dairy products such as cream, butter, yogurt, ice cream, and especially the more durable and easily transportable product, cheese. Industrial science has brought us casein, whey protein, lactose, condensed milk, powdered milk, and many other food-additive and industrial products.

Some mammals lose the ability to digest milk properly if a long period passes without consumption of it after weaning. In many ethnic groups, people lose the ability to digest milk after childhood (that is, they become lactose intolerant), so many traditional cuisines around the world, such as Chinese cuisine, do not feature dairy products. On the other hand, those groups that do continue to tolerate milk often have exercised great creativity in using the milk of domesticated ruminants, not only of cows, but also sheep, goats, yaks, water buffalo, horses, and camels.

The term milk is also used for whitish non-animal substitutes such as soy milk, rice milk, almond milk, and coconut milk. Even the regurgitated substance pigeons feed their young is called crop milk though it bears little resemblance to mammalian milk.


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Holstein cattle, the dominant breed in industrialized dairying today.

Milking has its advent in the very evolution of placental mammals. While the exact time of its appearance is not known, the immediate ancestors of modern mammals were much like monotremes, including the platypus. Such animals today produce a milk-like substance from glands on the surface of their skin, but without the nipple, for their offspring to drink after hatching from their eggs. Likewise, marsupials, the closest cousin to placental mammals, produce a milk-like substance from a teat-like organ in their pouches. The earliest immediate ancestor of placental mammals known seems to be eomaia, a small creature superficially resembling rodents, that is thought to have lived 125 million years ago, during the Cretaceous era. It almost certainly produced what would be considered milk, in the same way as modern placental mammals.

Animal milk is first known to have been used as human food at the beginning of animal domestication. Cow's milk was first used as human food in the Middle East. Goats and sheep were domesticated in the Middle East between 9000 and 8000 BC. Goats and sheep are ruminants: mammals adapted to survive on a diet of dry grass, a food source otherwise useless to humans, and one that is easily stockpiled. The animals were probably first kept for meat and hides, but dairying proved to be a more efficient way of turning uncultivated grasslands into sustenance: the food value of an animal killed for meat can be matched by perhaps one year's worth of milk from the same animal, which will keep producing milk — in convenient daily portions — for years (McGee 8–10).

Around 7000 BC, cattle were being herded in parts of Turkey. There is evidence of milk consumption in the British Isles during the Neolithic period. The use of cheese and butter spread in Europe, parts of Asia and parts of Africa. Domestic cows, which previously existed throughout much of Eurasia, were then introduced to the colonies of Europe during the Age of exploration.

Other milk animals

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Goat's milk can be used for other applications such as cheese and other dairy products.
In addition to cows, the following animals provide milk used by humans for dairy products: In Russia and Sweden, small moose dairies also exist.[2] Donkey and horse milk have the lowest fat content, while the milk of seals contains more than 50% fat.[3]

Whale's milk, not used for human consumption, is one of the highest-fat milks, containing up to 50% fat.[4] [5] The high fat content of whale's milk is not a product of cetacean's great size, as guinea pig milk has an average fat content of 46%.[6]

Human milk is not produced or distributed industrially or commercially; however, milk banks exist that allow for the collection of donated human milk and its redistribution to infants who may benefit from human milk for various reasons (premature neonates, babies with allergies or metabolic diseases, etc.).

All other female mammals do produce milk, but are rarely or never used to produce dairy products for human consumption.

Modern production

Main article: Dairy farming
Top Ten Milk Producers — 2005
(1000 tonnes)
 United States80,264.51
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 United Kingdom14,577
 New Zealand14,500
World Total372,353.31
Source: UN Food & Agriculture Organisation [1]
In the Western world today, cow's milk is produced on an industrial scale. It is by far the most commonly consumed form of milk in the western world. Commercial dairy farming using automated milking equipment produces the vast majority of milk in developed countries. Types of cattle such as the Holstein have been specially bred for increased milk production. According to McGee, 90% of the dairy cows in the United States and 85% in Great Britain are Holsteins (McGee 12). Other milk cows in the United States include Ayrshire, Brown Swiss, Guernsey, Jersey, and Milking Shorthorn. The largest producers of dairy products and milk today are India followed by the United States[7] and New Zealand.

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Milk output in 2005. Click the image for the details.


It was reported in 2007 that with increased world-wide prosperity and the competition of biofuel production for feedstocks, both the demand for and the price of milk had substantially increased world wide. Particularly notable was the rapid increase of consumption of milk in China and the rise of the price of milk in the United States above the government subsidized price.[8]

Physical and chemical structure

Milk is an emulsion of butterfat globules within a water-based fluid. Each fat globule is surrounded by a membrane consisting of phospholipids and proteins; these emulsifiers keep the individual globules from joining together into noticeable grains of butterfat and also protect the globules from the fat-digesting activity of enzymes found in the fluid portion of the milk. In unhomogenized cow's milk, the fat globules average about four micrometers across. The fat-soluble vitamins A, D, E, and K are found within the milkfat portion of the milk (McGee 18).

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Schematic of a micelle.
The largest structures in the fluid portion of the milk are casein protein micelles: aggregates of several thousand protein molecules, bonded with the help of nanometer-scale particles of calcium phosphate. Each micelle is roughly spherical and about a tenth of a micrometer across. There are four different types of casein proteins, and collectively they make up around 80 percent of the protein in milk, by weight. Most of the casein proteins are bound into the micelles. There are several competing theories regarding the precise structure of the micelles, but they share one important feature: the outermost layer consists of strands of one type of protein, kappa-casein, reaching out from the body of the micelle into the surrounding fluid. These Kappa-casein molecules all have a negative electrical charge and therefore repel each other, keeping the micelles separated under normal conditions and in a stable colloidal suspension in the water-based surrounding fluid[9] (McGee 19–20).

Both the fat globules and the smaller casein micelles, which are just large enough to deflect light, contribute to the opaque white color of milk. The fat globules contain some yellow-orange carotene, enough in some breeds — Guernsey and Jersey cows, for instance — to impart a golden or "creamy" hue to a glass of milk. The riboflavin in the whey portion of milk has a greenish color, which can sometimes be discerned in skim milk or whey products (McGee 17). Fat-free skim milk has only the casein micelles to scatter light, and they tend to scatter shorter-wavelength blue light more than they do red, giving skim milk a bluish tint.[10]

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A simplified representation of a lactose molecule being broken down into glucose and galactose.

Milk contains dozens of other types of proteins besides the caseins. They are more water-soluble than the caseins and do not form larger structures. Because these proteins remain suspended in the whey left behind when the caseins coagulate into curds, they are collectively known as whey proteins. Whey proteins make up around twenty percent of the protein in milk, by weight. Lactoglobulin is the most common whey protein by a large margin (McGee 20–21).

The carbohydrate lactose gives milk its sweet taste and contributes about 40% of whole cow milk's calories. Lactose is a composite of two simple sugars, glucose and galactose. In nature, lactose is found only in milk and a small number of plants (McGee 17). Other components found in raw cow milk are living white blood cells. Mammary-gland cells, various bacteria, and a large number of active enzymes are some other components in milk (McGee 16).


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A milking machine in action.
In most Western countries, a centralised dairy facility processes milk and products obtained from milk (dairy products), such as cream, butter, and cheese. In the United States, these dairies are usually local companies, while in the southern hemisphere facilities may be run by very large nationwide or trans-national corporations (such as Fonterra).

Pasteurization and raw milk

Pasteurization is used to kill harmful microorganisms by heating the milk for a short time and then cooling it for storage and transportation. Pasteurized milk is still perishable and must be stored cold by both suppliers and consumers. Dairies print expiration dates on each container, after which stores will remove any unsold milk from their shelves. In many countries it is illegal to sell milk that is not pasteurized.

Unfortunately, the heating destroys the vitamin C content and light further destroys other beneficial aspects of milk, being the reason that opaque containers are recommended for storage and transportation. Humans are among the few animals who cannot manufacture vitamin C so its presence in the natural milk of their mothers is essential for the health of human infants and vitamin supplements are necessary for human infants fed only pasteurized milk.

Milk may also be further heated to extend its shelf life through ultra-high temperature treatment (UHT), which allows it to be stored unrefrigerated, or even longer lasting sterilization.

Those preferring raw milk argue that the pasteurization process also kills beneficial microorganisms and other important nutritional constituents. The resulting pasteurized product is said to be less digestible, be less nutritious, and turns rancid (as opposed to ferment) with age. However, unpasteurized milk can harbor harmful disease-causing bacteria such as tuberculosis, brucellosis, salmonella, diphtheria, and escherichia coli.[11] The cows must be maintained in very sanitary conditions and a watchful eye kept as to disease testing and vaccinations for this to be completely safe. Cheeses made with raw milk are regarded as safer as the milk typically had to be heated to some extent anyway to make the cheese, and this would kill many of the dangerous organisms possibly present.

Creaming and homogenization

Upon standing for 12 to 24 hours, fresh milk has a tendency to separate into a high-fat cream layer on top of a larger, low-fat milk layer. The cream is often sold as a separate product with its own uses; today the separation of the cream from the milk is usually accomplished rapidly in centrifugal cream separators. The fat globules rise to the top of a container of milk because fat is less dense than water. The smaller the globules, the more other molecular-level forces prevent this from happening. In fact, the cream rises in cow milk much more quickly than a simple model would predict: rather than isolated globules, the fat in the milk tends to form into clusters containing about a million globules, held together by a number of minor whey proteins (McGee 19). These clusters rise faster than individual globules can. The fat globules in milk from goats, sheep, and water buffalo do not form clusters so readily and are smaller to begin with; cream is very slow to separate from these milks (McGee 19).
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Milk from Ireland.
Milk is often homogenized, a treatment which prevents a cream layer from separating out of the milk. The milk is pumped at high pressures through very narrow tubes, breaking up the fat globules through turbulence and cavitation.[12] A greater number of smaller particles possess more total surface area than a smaller number of larger ones, and the original fat globule membranes cannot completely cover them. Casein micelles are attracted to the newly-exposed fat surfaces; nearly one-third of the micelles in the milk end up participating in this new membrane structure. The casein weighs down the globules and interferes with the clustering that accelerated separation. The exposed fat globules are briefly vulnerable to certain enzymes present in milk, which could break down the fats and produce rancid flavors. To prevent this, the enzymes are inactivated by pasteurizing the milk immediately before or during homogenization. Homogenized milk tastes blander but feels creamier in the mouth than unhomogenized; it is whiter and more resistant to developing off flavors (McGee 23). Creamline, or cream-top, milk is unhomogenized; it may or may not have been pasteurized. Some have suggested that homogenized milk is harder to digest or not as suited to some people as is unhomogenized milk. Unlike pasteurization, homogenization confers no health or safety benefits to the milk, only the convenience of not needing to shake the bottle oneself.

Unhomogenized milk has made a small comeback in a few areas, such as the west coast of the United States where Straus Family Creameries, based originally out of Sonoma, sells one line of organic milk with the cream still on top in old-fashioned glass bottles. They still however pasteurize it to prevent harmful microorganisms.

Nutrition and health

The composition of milk differs widely between species. Factors such as the type of protein; the proportion of protein, fat, and sugar; the levels of various vitamins and minerals; and the size of the butterfat globules and the strength of the curd are among those than can vary.Introduction to Dairy Science and Technology, webpage of University of Guelph For example:
  • Human milk contains, on average, 1.1% protein, 4.2% fat, 7.0% lactose (a sugar), and supplies 72 kcal of energy per 100 grams.
  • Cow's milk contains, on average, 3.4% protein, 3.6% fat, and 4.6% lactose, and supplies 66 kcal of energy per 100 grams. See also Nutritional benefits further on.
Aquatic mammals, such as seals and whales, produce milk that is very rich in fats and other solid nutrients when compared with land mammals' milk.

Nutritional benefits

Cow milk (whole)
Nutritional value per 100 g (3.5 oz)
Energy 0 kcal   0 kJ
Carbohydrates     5.2 g
- Sugars  5.2 g
  - Lactose 5.2 g  
Fat3.25 g
- saturated  1.9 g
- monounsaturated  0.8 g  
- polyunsaturated  0.2 g  
Protein 3.2 g
Water88 g
Vitamin A equiv.  28 μg 0%
Thiamin (Vit. B1)  0.04 mg  0%
Riboflavin (Vit. B2)  0.18 mg  0%
Vitamin B12  0.44 μg  0%
Vitamin D  40 IU0%
Calcium  113 mg0%
Magnesium  10 mg0% 
Potassium  143 mg  0%
100 ml corresponds to 103 g.[13]
Percentages are relative to US
recommendations for adults.
Source: USDA Nutrient database

Processed milk began containing differing amounts of fat during the 1950s. A serving (1 cup or 250 ml) of 2%-fat milk contains 285 mg of calcium, which represents 22% to 29% of the daily recommended intake (DRI) of calcium for an adult. Depending on the age, 8 grams of protein, and a number of other nutrients (either naturally or through fortification): Studies show possible links between low-fat milk consumption and reduced risk of arterial hypertension, coronary heart disease,colorectal cancer and obesity. Overweight individuals who drink milk may benefit from decreased risk of insulin resistance and type 2 diabetes.[14]

Interestingly, a study has shown that for women desiring to have a child, those who consume full fat dairy products may actually slightly increase their fertility, while those consuming low fat dairy products may slightly reduce their fertility due to interference with ovulation. However, studies in this area are still inconsistent.[15]

Nutritional/physiological detriments

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  • Milk contains casein, a substance that breaks down in the human stomach to produce the peptide casomorphin, an opioid that appears to act as a histamine releaser, and is suspected in some cases to aggravate the symptoms of autism. [16]
  • Lactose intolerance, discussed below.
  • Milk that has not received a fat content reduction is rich in saturated fat and cholesterol, which numerous sources[Who?] have suggested as contributing to an increased risk of atherosclerosis and coronary heart disease when consumed in excessive quantity. Low-fat and non-fat forms of milk may mitigate this risk.
  • Cow milk allergy (CMA) is as an immunologically mediated adverse reaction to one or more cow's milk proteins. Rarely is it severe enough to cause death.
  • There are some[Who?] fringe groups debating the amount of calcium from milk that is actually absorbed by the human body.[17] However, calcium from dairy products has greater bio-availability than calcium from vegetable products. [18]
  • Several studies [Who?] have shown that men who drink large amount of milk and consume dairy products may increase their risk of developing Parkinson's disease. The reason behind this is, however, not fully understood and it also remains unclear why this is not the case for women.[19][20]
  • Several sources[Who?] suggest a correlation between high calcium intake (2000 mg per day, or twice the US recommended daily allowance, equivalent to six or more glasses of milk per day) and prostate cancer.[21] A large study specifically implicates dairy.[22] A review published by the World Cancer Research Fund and the American Institute for Cancer Research states that at least eleven human population studies have linked excessive dairy product consumption and prostate cancer, however randomized clinical trial data with appropriate controls only exists for calcium, not dairy produce, where there was no correlation.[23]

Controversy surrounding milk and milk production

A number of advocate groups[Who?] have sprung up protesting that milk presents a health threat. While whole and other fattened forms of milk contain a large amount of saturated fat and cholesterol, factors which are known contributors to the risk of heart disease and many individuals are lactose intolerant, no study has concluded any causal health risk to normal individuals consuming moderate quantities of skim and fat-free varieties of milk.

Common claims cited by anti-milk advocates:
  • White blood cells -- Milk contains varying levels of white blood cells, depending upon the health of the source animals; controversy surrounds whether these are simply somatic cells or pus.[24] In the United States, one to seven drops of these cells are in every eight-ounce glass of milk, varying by state, according to guidelines set up by the Food and Drug Administration and statistics reported by the dairy industry.[25] Only one state out of all fifty, Hawaii, has a cell count lower than the dairy industry's recommendations; seventeen states produce milk that would be illegal to sell based on somatic cell limits in Europe.
No study has ever conclusively demonstrated that the levels of white blood cells found in normal milk actually pose any health risk to normal individuals.
  • Bovine Growth Hormone(rbst) -- Since November 1993, with FDA approval, Monsanto has been selling recombinant bovine somatotropin (rbST)--or rBGH--to dairy farmers. Additional bovine growth hormone is administered to cattle in order to increase their milk production, though the hormone also naturally fosters liver production of insulin-like growth factor 1 (IGF1). The deposit thereof in the milk of rBGH-affected cattle has been the source of concern; however, all milk contains IGF1 since all milking cows produce bovine growth hormone naturally. The IGF1 in milk from rBGH-affected cattle does not vary from the range normally found in a non-supplemented cow.[26] Elevated levels of IGF1 in human blood has been linked to increased rates of breast, colon, and prostate cancer by stimulating their growth,[27][28] though this has not been linked to milk consumption. The EU has recommended against Monsanto milk.[29] In addition, the cows receiving rBGH supplements may more frequently contract an udder infection known as mastitis, partly responsible for the aforementioned prevalence of blood cells in dairy products.[30] Milk from rBGH-affected cattle is banned in Canada, Australia, New Zealand, and Japan due to the mastitis problems. On June 9, 2006 the largest milk processor in the world and the two largest supermarkets in the United States--Dean Foods, Wal-Mart, and Kroger--announced that they are "on a nationwide search for rBGH-free milk"
No study has indicated that consumption of rBST-produced milk increases IGF1 levels, nor has any study demonstrated an increased risk of any disease between those consuming rBST and non-rBST produced milk. In 1994, the FDA has concluded that no significant difference has been shown between milk derived from rBST-treated and non-rBST-treated cows, nor does any test exist which can differentiate between milk from rBST-treated and non-rBST treated cows. [31]

Lactose intolerance

Main article: lactose intolerance

Lactose, the disaccharide sugar component of all mammal, milk must be cleaved in the small intestine by the enzyme lactase in order for it's constituents (galactose and glucose) to be absorbed. The production of this enzyme declines significantly after weaning in all mammals including humans (except for most northern westerners and a few other ethnic groups, lactase decline occurs after weaning, sometime between the ages of two and five). Once lactase levels have dropped, consumption of even minute amounts of dairy can cause diarrhea, intestinal gas, cramps and bloating, as the undigested lactose travels through the gastrointestinal tract and serves as nourishment for intestinal microflora who excrete gas.

Nutrition - comparison by animal source

Milk Composition Analysis, per 100 grams
Constituents unit Cow Goat Sheep Water Buffalo
Sugars (Lactose)g4.
Fatty Acids:
Source: McCane, Widdowson, Scherz, Kloos.[2]

These compositions vary by breed, animal, and point in the lactation period. Jersey cows produce milk of about 5.2% fat, Zebu cows produce milk of about 4.7% fat, Brown Swiss cows produce milk of about 4.0% fat, and Holstein-Friesian cows produce milk of about 3.6% fat. The protein range for these four breeds is 3.3% to 3.9%, while the lactose range is 4.7% to 4.9%. [32]

Milk fat percentages in all dairy breeds vary according to digestible fibre, starch and oil intakes[33], and can therefore be manipulated by dairy farmers' diet formulation strategies. Mastitis infection can cause fat levels to decline.[34]

Varieties and brands

See also: Milk bottle top
Cow's milk is generally available in several varieties. In some countries these are:
  • Full cream (or "whole" in US and UK, "homo milk" in Canada & some US dairies, about 3.25% fat)
  • Semi-skimmed ("reduced fat" or "low fat", about 1.5-1.8% fat)
  • Skimmed (about 0.1% fat)
Milk in the U.S. and Canada is sold as:
  • Whole varieties
  • 2% (reduced fat)
  • 1% (low fat)
  • <0.5% (very low fat)
  • Skim (nearly no fat)
In Canada "whole" milk refers to creamline (unhomogenized) milk. "Homogenized" milk refers to milk which is 3.25% butterfat. Generally all store-bought milk in Canada has been homogenized. Yet, the term is also used as a name to describe butterfat content for a specific variety of milk. Modern commercial dairy processing techniques involve first removing all of the butterfat, and then adding back the appropriate amount depending on which product is being produced on that particular line.

In Britain, it is possible to get Channel Island milk, which is 5.5% fat.

In the United States, skim milk is also known as "fat free" milk, due to USDA regulations stating that any food with less than ½ gram of fat per serving can be labeled "fat free".

Full cream, or whole milk, has the full milk fat content (about 3-4% if Friesian- or Holstein-breed are the source). For skimmed or semi-skimmed milk, all of the fat content is removed and then some (in the case of semi-skimmed milk) is returned. The best-selling variety of milk is semi-skimmed; in some countries full-cream (whole) milk is generally seen as less healthy and skimmed milk is often thought to lack taste. Whole milk is recommended to provide sufficient fat for developing toddlers who have graduated from breast milk or infant formula.

In the United States and Canada, a blended mixture of half cream and half milk is often sold in small quantities and is called half-and-half. Half-and-half is used for creaming coffee and similar uses. In Canada, low-fat cream is available, which has half the fat content of half-and-half.

Organic Milk (in the United States) or Bio-Milk & Biologique Milk (in Europe) is milk produced without the use of chemical herbicides or pesticides, and generally with more natural fertilizers and higher standards for the animals, and is now easy to find on the shelves in many areas. Demeter certified milk is produced with Biodynamic agriculture methods and is similar in standards to organic milk and biological milk, with a few special farm procedures added that are biodynamic-specific.

Additives and flavored milk drinks

In countries where the cattle (and often the people) live indoors, commercially sold milk commonly has vitamin D added to it to make up for lack of exposure to UVB radiation.

Reduced fat milks often have added vitamin A to compensate for the loss of the vitamin during fat removal; in the United States this results in reduced fat milks having a higher vitamin A content than whole milk.[35]

To aid digestion in those with lactose intolerance, milk is available in some areas with added bacterial cultures such as Lactobacillus acidophilus ("acidophilus milk") and bifidobacteria ("a/B milk").[36] Another milk with Lactococcus lactis bacteria cultures ("cultured buttermilk") is often used in cooking to replace the traditional use of naturally soured milk, which has become rare due to the ubiquity of pasteurization which kills the naturally occurring lactococcus bacteria.[37]

Milk often has flavoring added to it for better taste or as a means of improving sales. Chocolate flavored milk has been sold for many years and has been followed more recently by such other flavors as strawberry and banana.

South Australia has the highest consumption of flavored milk per person in the world, where Farmers Union Iced Coffee outsells Coca-Cola, a success shared only by Inca Kola in Peru and Irn-Bru in Scotland.

Switzerland has a soft drink based on milk that tastes and looks much like SevenUp. This popular "milk-cola", named Rivella, is in fact the national soft drink and even comes complete in low calorie & low sugar varieties. In spite of what might be expected, it does not taste like milk.


Because milk spoils so easily, it should, ideally, be distributed as quickly as possible. In many countries milk used to be delivered to households daily, but economic pressure has made milk delivery much less popular, and in many areas daily delivery is no longer available. People buy it chilled at grocery or convenience stores or similar retail outlets. Prior to the widespread use of plastics, milk was sold in wax-coated paper containers; prior to that milk was often distributed to consumers in glass bottles; and before glass bottles, in bulk that was ladled into the customer's container.

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Glass milk bottles used for home delivery service
In the UK, milk can be delivered daily by a milkman who travels his local milk round (route) using a battery-powered milk float during the early hours. Milk is delivered in 1 pint glass bottles with aluminium foil tops. Silver top denotes full cream unhomogenized; red top full cream homogenized; red/silver top semi-skimmed; blue/silver check top skimmed; and gold top channel island.

Empty bottles are rinsed before being left outside for the milkman to collect and take back to the dairy for washing and reuse. Currently many milkmen operate franchises as opposed to being employed by the dairy and payment is made at regular intervals, by leaving a check; by cash collection; or direct debit.

Although there was a steep decline in doorstep delivery sales throughout the 1990s, the service is still prominent, as dairies have diversified and the service is becoming more popular again. The doorstep delivery of milk is seen as part of the UK's heritage, and is relied upon by people up and down the country.

In New Zealand, milk is no longer distributed in glass bottles. In rural India, milk is delivered daily by a local milkman carrying bulk quantities in a metal container, usually on a bicycle; and in other parts of metropolitan India, milk is usually bought or delivered in a plastic bags or cartons via-shops or supermarkets.

In the United States bottles were replaced with milk cartons, which are tall paper boxes with a square cross-section and a peaked top that can be folded outward upon opening to form a spout. Now milk is increasingly sold in plastic bottles. First the gallon and half-gallon sizes were sold in plastic jugs while the smaller sizes were sold in milk cartons. Recently milk has been sold in smaller resealable bottles made to fit in automobile cup holders.

The quarter-pint milk carton is the traditional unit as a component of school lunches. In the U.S., pictures of missing children were printed on the larger milk cartons as a public service until it was determined that this was disturbing to children.

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A brick of French UHT milk
Milk preserved by the UHT process is sold in cartons often called a "brik" (tm Tetra Pak) that lack the peak of the traditional milk carton. Milk preserved in this fashion does not need to be refrigerated before opening and has a longer shelf life than milk in ordinary packaging. It is more typically sold unrefrigerated on the shelves in Europe than in America.

Glass milk containers are now rare. Most people purchase milk in bags, plastic jugs or waxed-paper cartons. Ultraviolet light from fluorescent lighting can destroy some of the proteins in milk so many companies that once distributed milk in transparent or highly translucent containers are now using thicker materials that block the UV light. Many people feel that such "UV protected" milk tastes better.

Milk comes in a variety of containers with local variants:
  • Australia and New Zealand: Distributed in a variety of sizes, most commonly in Tetra Pak cartons for up to 1 litres, and plastic screw-top bottles beyond that with the following volumes; 1.1L, 2L, and 3L. 1 litre Bags are starting to appear in supermarkets, but have not yet proved popular. Most UHT-milk is packed in 1 or 2 litre paper containers with a sealed plastic spout.
  • Brazil: Used to be sold in cooled or frozen 1 litre bags, just like for South Africa. Nowadays the most common form is 1 litre Tetra Pak cartons containing skimmed, semi-skimmed or whole milk.
  • Canada: 1.33 litre plastic bags (sold as 4 litres in 3 bags) are widely available in some areas (especially Ontario and Québec), although the 4 litre plastic jug has supplanted them in western Canada. Other common packaging sizes are 2 litre, 1 litre, 500 millilitre, and 250 millilitre cartons, as well as 4 litre, 1 litre, 250 mL Tetra Pak cartons and 500 millilitre plastic jugs.
  • China: Sweetened milk is a drink popular with students of all ages and is often sold in small plastic bags complete with straw. Adults not wishing to drink at a banquet often drink milk served from cartons or milk tea.
  • Parts of Europe: Sizes of 500 millilitres, 1 litre (the most common), 2 litres and 3 litres are commonplace.
  • Hong Kong - milk is sold in glass bottles (220 mL), cartons (236 mL and 1L), plastic jugs (2 litres) and Tetra Pak cartons (250 mL).
  • India: Commonly sold in 500 mL plastic bags. It is still customary to serve the milk boiled, despite pasteurization. Milk is often buffalo milk. Flavored milk is sold in most convenience stores in waxed cardboard containers. Convenience stores also sell many varieties of milk (such as flavored and ultra-pasteurized) in different sizes, usually in Tetra Pak cartons.
  • Israel: Non-UHT milk is most commonly sold in 1 litre waxed cardboard boxes and 1 litre plastic bags. It may also be found in 0.5L and 2L waxed cardboard boxes, 2L plastic jugs and 1L plastic bottles. UHT milk is available in 1 litre (and less commonly also in 0.25L) carton "bricks".
  • Japan: Commonly sold in 1 litre waxed cardboard boxes. In most city centers there is also home delivery of milk in glass jugs. As seen in China, sweetened and flavored milk drinks are very popular to see in vending machines.
  • South Africa: Commonly sold in 1 litre bags. The bag is then placed in a plastic jug and the corner cut off before the milk is poured.
  • South Korea: sold in cartons (180mL, 200mL, 500mL 900mL, 1L, 1.8L, 2.3L), plastic jugs (100Ml and 1.8L), Tetra Pak cartons (180mL and 200mL) and plastic bags (100mL).
  • Poland: UHT milk is mostly sold in Tetra Pak cartons (500mL, 1L, 2L), and non-UHT in 1L plastic bags or plastic bottles. Milk, UHT is commonly boiled, despite being pasteurized.
  • Turkey: Commonly sold in 500 mL or 1L cartons or special plastic bottles. UHT milk is more popular. Milkmen also serve in smaller towns and villages.
  • United Kingdom: Most stores still stock Imperial sizes: 1 pint (568 mL), 2 pints (1.136 L), 4 pints (2.273 L), 6 pints (3.408 L) or a combination including both metric and imperial sizes. Glass milk bottles delivered to the doorstep by the milkman are typically pint-sized and are returned empty by the householder for repeated reuse. Milk is also sold at supermarkets in either Tetra Pak cartons or HDPE bottles. Milk can still be legally sold by the Imperial pint in reusable bottles in the UK under EU regulations (a distinction only shared with beer and cider), whilst a growing number of manufacturers such as Northern Foods now sell milk in 1 and 2 litre bottles.
  • United States: Commonly sold in gallon, half-gallon and quart containers (U.S. customary units) of rigid plastic or, occasionally for sizes less than a gallon, waxed cardboard, although bottles made of opaque PET are starting to become more commonplace in all smaller sizes. The US single-serving size is usually the half-pint (about 240 ml). Occasionally dairies will deliver milk straight to customers in coolers filled with glass bottles (usually half-gallon). Some convenience store chains in the United States (such as Kwik Trip in the Midwest) sell milk in 1/2 gallon bags.
  • Uruguay: Commonly sold in 1 litre bags. The bag is then placed in a plastic jug and the corner cut off before the milk is poured.
Practically everywhere, condensed milk and evaporated milk is distributed in metal cans, 250 and 125 ml paper containers and 100 and 200 mL squeeze tubes, and powdered milk (skim and whole) is distributed in boxes or bags.

Enlarge picture
Brazilian Yakult, an example of the use of milk.


When raw milk is left standing for a while, it turns "sour". This is the result of fermentation: lactic acid bacteria turning the sugar inside the milk into lactic acid. This fermentation process is exploited in the production of various dairy products such as cheese and yogurt. There are four noted periods of milk decay:
  • Rancid — also called "on the turn"; milk is still consumable at this stage
  • Curdling — separation of curd and whey will occur but may still be consumable
  • Coagulation — beyond use; a period of aromatic decay sets in accompanied by mold
  • Dry — beyond use; the milk has dehydrated and become hard and chalky
Pasteurized cow's milk, on the other hand, spoils in a way that makes it unsuitable for consumption. This causes it to assume an unpleasant odor and pose a high danger of food poisoning, if ingested. In raw milk, the naturally-occurring lactic acid bacteria, under suitable conditions, quickly produce large amounts of lactic acid. The ensuing acidity in turn prevents other germs from growing, or slows their growth significantly. Through pasteurization, however, these lactic acid bacteria are mostly destroyed, which means that other germs can grow unfettered and thus cause decomposition.

In order to prevent spoilage, milk can be kept refrigerated and stored between 1 and 4 degrees Celsius in bulk tanks. Most milk is pasteurized by heating briefly and then refrigerated to allow transport from factory farms to local markets. The spoilage of milk can be forestalled by using ultra-high temperature (UHT) treatment; milk so treated can be stored unrefrigerated for several months until opened. Sterilized milk, which is heated for a much longer period of time, will last even longer, but also lose more nutrients and assume a still different taste. Condensed milk, made by removing most of the water, can be stored in cans for many years, unrefrigerated, as can evaporated milk. The most durable form of milk is milk powder, which is produced from milk by removing almost all water. The moisture content is usually less than 5% in both drum and spray dried milk powder.

Milk in language and culture

The importance of milk in human culture is attested to by the numerous expressions embedded in our languages, for example "the milk of human kindness". In ancient Greek mythology, the goddess Hera spilled her breast milk after refusing to feed Heracles, resulting in the Milky Way.

In African and Asian developing nations, butter is traditionally made from fermented milk rather than cream. It can take several hours of churning to produce workable butter grains from fermented milk.[38]

Holy books have also mentioned milk; the Bible contains references to the Land of Milk and Honey. In the Quran, there is a request to wonder on milk as follows: 'And surely in the livestock there is a lesson for you, We give you to drink of that which is in their bellies from the midst of digested food and blood, pure milk palatable for the drinkers.'(16-The Honeybee, 66). The Ramadhan fast is traditionally broken with a glass of milk and dates.


1. ^ . . . or just go with the flow?. The Times, May 5, 2005.
2. ^ "Moose milk makes for unusual cheese", The Globe and Mail, 26 June 2004. Retrieved on 2007-08-27.2004"> 
3. ^ Milk From Cows and Other Animals, web page by Washington Dairy Products Commission
4. ^ MSN encarta
5. ^
6. ^ Morales, Edmundo (1995). The Guinea Pig : Healing, Food, and Ritual in the Andes. University of Arizona Press. ISBN 0-8165-1558-1. 
7. ^ FAO Food outlook: International dairy product prices are turning down: how far, how fast? FAO online publication, 1 June 2006
8. ^ "A Thirst for Milk Bred by New Wealth Sends Prices Soaring" article by Wayne Arnold in the New York Times September 4, 2007
9. ^ Dairy Chemistry and Physics, webpage of University of Guelph
10. ^ Dairy Chemistry and Physics, webpage of University of Guelph
11. ^ Raw Milk Vs. Pasteurized Milk. Reproduction from Armchair Science, London 1938.
12. ^ Homogenization of Milk and Milk Products, webpage of University of Guelph
13. ^ Density of milk
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18. ^ Brody T. Calcium and phosphate. In: Nutritional biochemistry. 2nd ed. Boston: Academic Press, 1999:761–94
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20. ^ "Milk linked to Parkinson's risk", BBC News. 
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23. ^ Chan JM et al., (2005) Role of diet in prostate cancer development and progression. J Clin Oncol 23:8152-60.
24. ^ Cohen, Rob. Your state's average pus count. Web page of the anti-dairy Dairy Education Board
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28. ^ Pacher, M. et al., Impact of constitutive IGF1/IGF2 stimulation on the transcriptional program of human breast cancer cells. Carcinogenesis. 2006 Jun 14
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38. ^ Crawford et al, part B, section III, ch. 1: Butter. Retrieved 28 November 2005.


See also

External links

Wikibooks has an article on
Mammary glands are the organs that, in the female mammal, produce milk for the sustenance of the young. These exocrine glands are enlarged and modified sweat glands and are the characteristic of mammals which gave the class its name.
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Linnaeus, 1758

Subclasses & Infraclasses
  • Subclass †Allotheria*
  • Subclass Prototheria
  • Subclass Theria

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C.L. Bonaparte, 1837


Monotremes (from the Greek monos 'single' + trema
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In humans, there are four kinds of sudoriferous or sweat glands which differ greatly in both the composition of the sweat and its purpose.
  • eccrine glands - sweat (normal sweat used in temperature control)
  • apocrine glands - sweat,fats,proteins (slightly more viscous sweat)

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Digestion is the process of metabolism whereby a biological entity processes a substance in order to chemically and mechanically convert the substance for the body to use.


Digestion occurs at the multicellular, cellular, and sub-cellular levels, usually in animals.
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Lactation describes the secretion of milk from the mammary glands, the process of providing that milk to the young, and the period of time that a mother lactates to feed her young.
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Colostrum (also known as beestings or first milk) is a form of milk produced by the mammary glands in late pregnancy and the few days after giving birth.

Human and bovine colostrums are thick, sticky and yellowish.
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Antibodies (also known as immunoglobulins) are proteins that are found in blood or other bodily fluids of vertebrates, and are used by the immune system to identify and neutralize foreign objects, such as bacteria and viruses.
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Types of Fats in Food
  • Unsaturated fat
  • Monounsaturated fat
  • Polyunsaturated fat
  • Trans fat
  • Omega: 3, 6, 9

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Proteins are large organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues.
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Calcium (IPA: /ˈkalsiəm/) is the chemical element in the periodic table that has the symbol Ca and atomic number 20. It has an atomic mass of 40.078.
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Vitamin C or L -ascorbate is an essential nutrient for higher primates, and a small number of other species. The presence of ascorbate is required for a range of essential metabolic reactions in all animals and in plants and is made internally by almost all organisms,
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Breastfeeding is the feeding of an infant or young child with milk from a woman's breasts. Babies have a sucking reflex that enables them to suck and milk.

With few exceptions, human breast milk is the best source of nourishment for human infants.
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Cream (from Greek chrisma) is a dairy product that is composed of the higher-butterfat layer skimmed from the top of milk before homogenization. In un-homogenized milk, over time, the lighter fat rises to the top.
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Butter is a dairy product, made by churning fresh or fermented cream or milk. Butter is used as a spread and a condiment, as well as in cooking applications such as baking, sauce making, and frying.
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Yoghurt or yogurt, or less commonly yoghourt or yogourt (see spelling below), is a dairy product produced by bacterial fermentation of milk. Fermentation of the milk sugar (lactose) produces lactic acid, which acts on milk protein to give yoghurt its
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Ice cream or ice-cream (originally iced cream) is a frozen dessert made from dairy products, such as cream (or substituted ingredients), combined with flavorings and sweeteners, such as sugar.
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Cheese is a solid food made from the milk of cows, goats, sheep and other mammals. Cheese is made by coagulating milk. This is accomplished by first acidification with a bacterial culture and then employing an enzyme, rennet (or rennet substitutes) to coagulate the milk to "curds
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Casein (from Latin caseus "cheese") is the most predominant phosphoprotein found in milk and cheese. When coagulated with rennet, casein is sometimes called paracasein.
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Whey protein is the name for a collection of globular proteins that can be isolated from whey, a by-product of cheese manufactured from cow's milk. It is typically a mixture of beta-lactoglobulin (~65%), alpha-lactalbumin (~25%), and serum albumin (~8%), which are soluble in their
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Lactose is a disaccharide that consists of β-D-galactose and β-D-glucose molecules bonded through a β1-4 glycosidic linkage. Lactose makes up around 2-8% of the solids in milk. The name comes from the Latin word for milk, plus the -ose ending used to name sugars.
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Condensed milk, also known as sweetened condensed milk, is cow's milk from which water has been removed and to which sugar has been added, yielding a very thick, sweet product that can last for years without refrigeration if unopened.
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Powdered milk is a powder made from dried (dehydrated) milk solids. Powdered milk has a far longer shelf life than liquid milk and does not need to be refrigerated due to its low moisture content.
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ethnic group or ethnicity is a population of human beings whose members identify with each other, usually on the basis of a presumed common genealogy or ancestry.[1] Ethnicity is also defined from the recognition by others as a distinct group[2]
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Lactose intolerance
Classification & external resources

Lactose, a disaccharide of β-D-galactose &
β-D-glucose, that is normally split by lactase.
ICD-10 E 73.
ICD-9 271.
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Cuisine (from French cuisine, "cooking; culinary art; kitchen"; ultimately from Latin coquere, "to cook") is a specific set of cooking traditions and practices, often associated with a specific culture.
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Chinese cuisine (Chinese: 中國菜) originated from different regions of China and has become widespread in many other parts of the world — from East Asia to North America, Australasia and Western Europe.
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Dairy products are generally defined as foodstuffs produced from milk.They are usually high-energy-yielding food products. A production plant for such processing is called a dairy or a dairy factory.
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