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Milk

2007 Schools Wikipedia Selection. Related subjects: Drink

   A glass of cow's milk
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   A glass of cow's milk

   Milk is the nutrient fluid produced by the mammary glands of female
   mammals (including monotremes). 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 more
   diverse foods. 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 both the mother and baby.

   The exact components of milk vary by species, but it contains
   significant amounts of saturated fat, protein and calcium. These
   amounts are not large in comparison to other foods rich in them,
   including coconuts, fish, and kale respectively, because milk is
   predominantly composed of water. 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.

   Humans, like other mammals, can consume mother's milk during their
   infancy. 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 do not feature dairy products. On
   the other hand, those cultures that do tolerate milk have often
   exercised great creativity in using the milk of domesticated ruminants,
   especially cows, but also sheep, goats, yaks, water buffalo, horses and
   camels. For millenia,s milk has been processed into dairy products such
   as cream, butter, yogurt, ice cream, and especially the storable and
   transportable cheese. Industrial science has brought us casein, whey
   protein, lactose, condensed milk, powdered milk, and many other
   food-additive and industrial products.

   Human milk is fed to infants through breastfeeding, either directly or
   by expressing the milk to be stored and consumed later.

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

History

   Holstein cattle, the dominant breed in industrialized dairying today.
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   Holstein cattle, the dominant breed in industrialized dairying today.

   Animal milk was first 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 BCE. 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 BCE, 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.

   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. 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 USA and New Zealand.

   Insert non-formatted text hereInsert non-formatted text here==Other
   milk animals==
   Goat's milk can be used for other applications such as cheese and other
   dairy products.
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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 for dairy
   products:
     * Sheep (the ewe)
     * Goats (the nanny)
     * Horses (the mare)
     * Donkeys
     * Camels (including the South American camelids)
     * Yaks
     * Water buffalo
     * Reindeer

   In Russia and Sweden, small moose dairies also exist. Donkey and horse
   milk have the lowest fat content, while the milk of seals contains more
   than 50% fat.

   Whale's milk, not used for human consumption, is one of the highest-fat
   milks. It contains, on average, 10.9% protein, 42.3% fat, and 2.0%
   lactose, and supplies 443 kcal of energy per 100 grams.

   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.).

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).
   Schematic of a micelle.
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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 roughtly 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 (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 colour 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 colour, 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.
   A simplified representation of a lactose molecule being broken down
   into glucose and galactose.
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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 (McGee 16).

Processing

   A milking machine in action.
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   A milking machine in action.

   In North America a dairy facility processes milk and products obtained
   from milk (dairy products), such as cream, butter, and cheese. Most
   dairies are local companies, as opposed to large or nationwide
   companies found in the southern hemisphere.

Pasteurization and raw milk

   Pasteurization kills many 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.

   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 important nutritional constituents.
   The resulting pasteurized product is said to contribute to its own
   indigestability, be less nutritious, and turn rancid (as opposed to
   sour) with age. However, unpasteurized milk can harbour harmful
   disease-causing bacteria such as tuberculosis, salmonella, diphtheria,
   polio, and escherichia coli.

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 quicker 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 as readily and are smaller to begin with; cream is very slow
   to separate from these milks (McGee 19).

   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. 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 flavours (McGee 23). Creamline, or
   cream-top, milk is unhomogenized; it may or may not have been
   pasteurized.

Additives

   Milk, sold commercially in countries where the cattle (and often the
   people) live indoors, commonly has vitamin D added to it to make up for
   lack of exposure to UVB radiation. 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 flavours as strawberry and banana.

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

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.

Nutritional benefits

              Cow milk (whole)
   Nutritional value per 100 g
          Energy 60 kcal   250 kJ

   Carbohydrates                   5.2 g
   - Sugars  5.2 g
     - Lactose 5.2 g
   Fat                             3.25 g
   - saturated  1.9 g
   - monounsaturated  0.8 g
   - polyunsaturated  0.2 g
   Protein                         3.2 g
   Water                           88 g
   Vitamin A  28 μg                3%
   Thiamin (Vit. B1)  0.04 mg      3%
   Riboflavin (Vit. B2)  0.18 mg   12%
   Vitamin B12  0.44 μg            18%
   Vitamin D  40 IU                20%
   Calcium  113 mg                 11%
   Magnesium  10 mg                3%
   Potassium  143 mg               3%
        100 g corresponds to 103 ml.
   Percentages are relative to US
   recommendations for adults.
   Source: USDA Nutrient database

   Milk began containing differing amounts of fat during the 1950's. 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):
     * Vitamins D and K are essential for bone health.
     * Iodine is a mineral essential for thyroid function.
     * Vitamin B12 and riboflavin are necessary for cardiovascular health
       and energy production.
     * Biotin and pantothenic acid are B vitamins important for energy
       production.
     * Vitamin A is critical for immune function.
     * Potassium and magnesium are for cardiovascular health.
     * Selenium is a cancer-preventive trace mineral.
     * Thiamine is a B-vitamin important for cognitive function,
       especially memory
     * Conjugated linoleic acid is a beneficial fatty acid that inhibits
       several types of cancer in mice, it has been shown to kill human
       skin cancer, colorectal cancer and breast cancer cells in vitro
       studies, and may help lower cholesterol and prevent
       atherosclerosis; only available in milk from grass-fed cows.

   Studies show possible links between low-fat milk consumption and
   reduced risk of arterial hypertension, coronary heart disease, and
   obesity. Overweight individuals who drink milk may benefit from
   decreased risk of insulin resistance and type 2 diabetes.

Nutritional/physiological detriments

   Consumption of cow's milk and its byproducts (hereafter referred to as
   "milk") are reported as 'unhealthy' primarily due to their high
   saturated fat and cholesterol content. The following additional issues
   are often cited as warranting consideration:
     * Lactose intolerance, discussed below.
     * Milk that has not received a fat content reduction is rich in
       saturated fat and cholesterol, which numerous sources have
       suggested as contributing to an increased risk of atherosclerosis
       and coronary heart disease. 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 it is severe
       enough to cause death.
     * 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, in an alternate form, pus . 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 . 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.
     * Since November 1993, with FDA approval, Monsanto has been selling
       recombinant bovine somatotropin (rbST)--or rBGH--to dairy farmers.
       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. The IGF1 in
       milk from rBGH-affected cattle does not vary from the range
       normally found in a non-supplemented cow. Elevated levels of IGF1
       in human blood has been linked to increased rates of breast, colon,
       and prostate cancer by stimulating their growth , though this has
       not been linked to milk consumption. The EU has recommended against
       Monsanto milk. In addition, the cows frequently contract an udder
       infection known as mastitis, partly responsible for the
       aforementioned prevalence of blood cells in dairy products . 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 ."
     * Several sources 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 . A large study specifically implicates dairy . 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 dairy product consumption and
       prostate cancer.

Lactose intolerance

   Lactose is a simple sugar that is present in all milk of the species of
   origin, and is digested with the help of the enzyme lactase. The
   production of this enzyme declines significantly after weaning in all
   mammals, including human beings. Lactose intolerance is the condition
   in which lactase is not produced in adulthood. With lactose
   intolerance, the result of consuming too much lactose is excess gas
   production and often diarrhea. Lactose-intolerant adults can drink
   about a cup (250 ml or 8 oz) of milk per day without severe symptoms.

   Most adults in the world are lactose-intolerant (McGee 14: "lactose
   tolerant adults are a distinct minority on the planet").
   Lactose-intolerant adults stop producing significant amounts of lactase
   sometime between the ages of two and five. A relatively recent genetic
   change caused some populations (McGee 14: "several thousand years
   ago"), including many Northern Europeans, to continue producing lactase
   into adulthood.

Distribution

   Glass milk bottles used for home delivery service
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   Glass milk bottles used for home delivery service
   A brick of French UHT milk
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   A brick of French UHT 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 often
   distributed to consumers in glass bottles, and before that in bulk that
   was ladled into the customer's container. In the UK, milk can be
   delivered daily by a milkman who travels his local milk round (route)
   using a battery-powered milk float, although this is becoming less
   popular as a result of supermarkets selling milk at lower prices. In
   New Zealand, milk is no longer distributed in glass bottles. In India,
   milk is sold in plastic sachet.

   In the United States bottles were replaced with milk cartons, which are
   tall boxes with a square cross-section and a peaked top that can 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 half-pint milk carton is the traditional unit as a component of
   school lunches. In the US, 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.

   Milk preserved by the UHT process is sold in cartons often called a
   "brick" 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.

   Glass milk containers are rare these days. Most people purchase milk in
   plastic jugs or bags or in waxed-paper cartons, such as those made by
   Tetra Pak. 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 harmful rays. Many people feel that such "UV
   protected" milk tastes better.

   Milk comes in a variety of containers with local variants:
     * 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. The US
       single-serving size is usually the half-pint (about 240 ml).
     * 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.
     * Parts of Europe: Sizes of 500 millilitres, 1 litre (the most
       common), 2 litres and 3 litres are commonplace.
     * United Kingdom: Most stores stock Imperial sizes: 1 pint (568 mL),
       2 pints (1.136 L), 4 pints (2.273 L), 6 pints (3.408 L) or, rarely,
       a combination including both metric and imperial sizes. Glass milk
       bottles delivered to the doorstep by the milkman are pint-sized and
       are returned empty by the householder for repeated recycling. Milk
       is also sold at supermarkets in either Tetra-Pak cartons or plastic
       bottles, also measured in pints. Milk continues to be legally sold
       by the Imperial pint in the UK under EU regulations (a distinction
       only shared with beer).
     * 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 litre
       paper containers with a sealed plastic spout.
     * 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.
     * 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.
     * India: Milk is often delivered daily to most urban homes in plastic
       bags. It is still customary to serve the milk boiled, despite
       pasteurization. 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.
     * 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 milk drinks are very popular to see in vending
       machines.
     * 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.
     * 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).

   Condensed 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.
     * 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).

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

Varieties and brands

   Cow's milk is generally available in several varieties. In some
   countries these are:
     * Full cream (or "whole" in US, "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.

Spoilage

   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 mould)
     * 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
   odour 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.

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", and the ways we have used it to name the visible world, for
   example the Milky Way.

   Milk is drunk as an accompaniment to meals in North America, whereas
   Europeans do not habitually do so after childhood.

   In African and Asian developing nations, butter is traditionally made
   from sour milk rather than cream. It can take several hours of churning
   to produce workable butter grains from fermented milk.
   Retrieved from " http://en.wikipedia.org/wiki/Milk"
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