Milk

For other uses, see Milk (disambiguation).

File:Milk l de.jpg

A glass of cow's milk

Milk most often means the nutrient fluid produced by the mammary glands of female mammals. It provides the primary source of nutrition for newborns before they are able to digest more diverse foods. It is also processed into dairy products such as cream, butter, yoghurt, ice-cream, gelato, cheese, casein, whey protein, lactose, condensed milk, dried milk, and many other food-additive and industrial products.

It can also be used to mean

• the white juice and the processed meat of the coconut in, more or less, liquid form, used especially in Thai, Indian (Kerala), and Polynesian cuisine.
• a non-animal substitute such as soya milk, rice milk, and almond milk.

Human milk is fed to infants through breastfeeding, either directly or by the female expressing her milk to be saved and fed later. The early lactation milk is known as colostrum, and carries the mother's antibodies to the baby.

Composition and nutrition

The composition of milk varies greatly among different mammals.

• Human breast milk is thin and high in lactose, its primary sugar.
• Cow's milk is lower in sugar and higher in protein, and is composed of about 3.5% to 6.5% milkfat, 4% to 8.5% milk solids and about 88% water. Its main protein (80%) is casein, while whey proteins make up most of the rest.

Lactose in milk is digested with the help of the enzyme lactase produced by the bodies of infants. In humans, production of lactase falls off towards adulthood (depending on the person's ethnic origin), in many cases to the point where lactose becomes indigestible, leading to lactose intolerance, a gastrointestinal condition that afflicts many.

There is some controversy over whether consumption of cow's milk is good for adult humans. While milk is often touted as healthy for its significant amount of calcium, required for healthy bone growth and nerve function, there is some disputed research to suggest that proteins in milk interfere with the use of its calcium to form bones by increasing the acidity level of the blood and triggering a response which balances that acidity level by leeching calcium that is presently in bones. However, the composition of milk differs widely from species to species; cow's milk is a completely different substance than goat's milk for instance, which any person who tastes both will recognize. Such factors as the lactose content, the proportion of and size of the butterfat globule and the strength of the curd, formed by the human enzymes digesting the milk, can differ from breed to breed and mammal to mammal.

Cow's milk

Cow's milk is most often produced on an industrial scale for human consumption. It is the most commonly consumed form of milk. Dairy farming has become such a large business that in many countries the process is highly automated; for example farmers use machines that attach directly to the cow's udder to milk a large number of cows.

There are special varieties of cows. Some are efficient at milk production, such as Holstein cows; others are good for beef production.

Commercial processing of milk

a cow-milking machine in action

A dairy is a facility for processing milk and other products obtained from milk (dairy products), such as cream, etc. Most dairies are local companies (as opposed to large nationwide companies).

Upon standing, fresh milk has a tendency to separate out into two layers; most goes to a lower-fat milk layer and some rises to a high-fat cream layer on top of the milk layer. Cream is often sold as a separate product with its own uses. In the United States, a blended mixture of half cream and half milk is often sold in smaller quantities and is called half and half; half and half is often used for creaming coffee and similar uses.

Milk produced for commercial consumption can undergo several processes. Pasteurization is heating milk for a short time to kill harmful micro-organisms, followed by cooling for storage and transportation. Such milk is still perishable and must be stored cold by both suppliers and consumers. Milk is sold by certain expiration dates written on each container by the dairy. Another process for commercial milk is homogenization, which produces milk in a single phase (or layer).

Milk sold commercially commonly has vitamin D added to it. Sometimes milk has flavoring added to it for better taste. For many years, chocolate-flavored milk has been available, but in recent years a few other flavors of milk and cream have become available. Chocolate milk can either be made by the milk producer or by the consumer, by adding chocolate flavoring in powder or syrup form.

South Australia has the highest consumption of flavoured milk per person, and is the only place in the world where a commercial beverage (Farmers Union Iced Coffee) outsells Coca-Cola

Health

Support

Cow's milk is argued to be healthy primarily due to its protein and calcium content. It is also a good source of a number of vitamins. A serving of 2%-fat milk contains 30% of the daily recommended intake (DRI) of calcium as part of a 2,000 calorie diet, 8 grams of protein, and a number of other nutrients (either naturally or through fortification):

• Vitamins D and K - essential for bone health
• Iodine - a mineral essential for thyroid function
• Vitamin B12 and Riboflavin - necessary for cardiovascular health and energy production
• Biotin and Pantothenic Acid - B vitamins important for energy production
• Vitamin A - critical for immune function
• Potassium and Magnesium - for cardiovacular health
• Selenium - cancer-preventive trace mineral
• Thiamin - B-vitamin important for cognitive function, especially memory
• Conjugated Linoleic Acid - beneficial fatty acid that inhibits several types of cancer in mice, has been shown to kill human skin cancer, colorectal cancer and breast cancer cells in in vitro studies, and may help lower cholesterol and prevent atherosclerosis; only available in milk from grass-fed cows

Milk supporters point out that 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.[1]

Criticism

Cow's milk is also argued to be unhealthy primarily due to its fat and cholesterol content. The following studies are used to support this position:

• Two studies suggested that galactose, which is produced in the digestion of lactose in milk, can be a cause of ovarian cancer.[2][3]
• One study suggests an association between high calcium intake and prostate cancer.[4] There is no evidence that any such problem is specific to milk.
• Some milk is rich in saturated fat, which studies have linked to increased risk of atherosclerosis and coronary heart disease. Low-fat and non-fat forms of milk may mitigate any such risk.
• As many as 70% of humans may suffer from some degree of lactose intolerance. For those individuals, milk may induce symptoms such as cramping, bloating, gas, and diarrhea.
• Critics question the claim that drinking large amounts of milk can reduce the risk of bone fractures, especially in the elderly. Some studies have failed to associate high calcium intakes with lower risk of hip and forearm fractures in men[5] or women[6]. acne[7].
• Some critics of milk claim that plant-based sources of calcium are preferable, on the grounds that animal proteins in milk may "leach" calcium from bones.[8] Such critics challenge the mainstream belief that milk lowers the risk of osteoporosis.
• A study published in June 2005 suggests that consumption of milk by 9- to 14-year-old children is associated with weight gain, although the researchers identify that excessive calorie intake is the cause rather than dairy specific factors. Researchers were surprised by their conclusion that weight gain was associated with dietary calcium and low-fat or skim milk, but not dairy fat.[9]

Scientific evidence has also been unable to support the claim that the consumption of cow’s milk as a source of calcium reduces the risk of osteoporosis. On the contrary, epidemiological research has linked the countries with the highest dairy consumption rates (i.e., the United States, Sweden and Finland) to the incidence of osteoporosis. The touted high protein content of cow’s milk can also cause difficulties in that the animal protein contained in milk acts to block the absorption of calcium and can cause the human body to produce antibodies which are believed to damage the pancreas, leading to the development of type 1 diabetes. In children, cow’s milk consumption has been linked to numerous diseases and cancers, including anemia, colic, allergies, and asthma. In adults, cow's milk consumption has been related to heart disease, prostate cancer and breast cancer. Additionally, the milk sugar lactose and its resultant galactose have been linked to an increased risk of ovarian cancer. A review published by the World Cancer Research Fund and the American Institute for Cancer Research has stated that at least 11 human population studies have linked dairy product consumption and prostate cancer.

Recombinant bovine stomatotropin (rBST), a synthetic growth hormone approved by the FDA, is used to increase the production of milk and can cause cows to suffer more frequent bouts of mastitis. This increase in disease results in an increase in the administered antibiotics which may end up in the milk supply.

The nutritional makeup of cow's milk is much different from human milk. One cup of human milk has 70% less protein, 38% more fat, and 47% more carbohydrates than cow's milk. Vitamic C, folic acid, sodium, iron and calcium levels also differ significantly.

Ethics

Animal-rights activists and others criticize the widespread consumption of cow's milk by humans by raising ethical issues associated with its consumption.

Distribution

Glass milk bottles used for home delivery service

Because of the perishable nature of milk, expeditious distribution is desirable. Milk used to be delivered by milkmen, but this is usually no longer economically feasible. Now it is available chilled at grocery and convenience stores and similar retail outlets. Prior to the widespread use of plastics, milk was usually commercially distributed to consumers in glass bottles. In the UK, milk can be delivered daily by a milk man who travels his local milk round (route) on an electric milk float, although this is becoming less popular as a result of supermarkets selling milk at cheaper prices. In New Zealand in some urban areas milk is still delivered to customers' homes.

Glass containers are rare these days. Most people purchase milk in plastic jugs or bags or in 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 vessels are starting to use thicker materials that block the harmful rays. Many people feel that such "UV protected" milk tastes better.

In the United States, milk is commonly sold in gallon, half-gallon and quart containers (U.S. customary units) of rigid plastic or waxed cardboard. The U.S. single serving size is usually the half-pint. In much of Canada, a 1 1/3 litre plastic bag (sold as 4 litres in 3 bags) is the most common, while 2 litre, 1 litre, 500 millilitre, and 250 millilitre cartons are also available. In Europe, metric sizes of 500 millilitres, 1 litre (the most common), 2 litres and 3 litres are commonplace (in the UK, some stores instead still stock the equivalents of old Imperial sizes: 568 ml (1 pint), 1.136 l (2 pints), 2.273 l (4 pints), or rarely a combination including both metric and imperial sizes, such as a choice of 568 ml, 1 l, 2 l and 3 l containers).

Condensed milk is distributed in metal cans and powdered milk is distributed in boxes or bags.

Varieties and brands

Cow's milk is generally available in several varieties. In some countries these are:

• full cream (or "whole" in North America)
• 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 percent" (reduced fat)
• "1 percent" (low fat)
• "1/2 percent" (low fat)
• "skim" (very low fat)

Note: In Canada "whole" milk refers to unhomogenized milk. "Homogenized" milk (or "Homo milk" in short) 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.

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.

There are many brands of milk currently; most milk brands vary little from each other. These brands include, in the United States and Canada:

• Alpenrose
• Anchor (a brand from Fonterra)
• Beatrice (a subsidiary of Parmalat in Canada - since March of 1997)
• Cumberland Farms
• Dairy Farmers
• H.P. Hood
• Leche Caparra
• Leche Suiza
• Lock City Dairies
• Lucerne
• Parmalat
• Pauls (a subsidiary of Parmalat in Australia)
• Pura
• Quality Chekd-A association of independent dairies whose members carry the "QChekd" seal
• Shamrock Milks
• Tenuvah
• United Dairy Farmers
• Vinamilk
• Wawa Dairy
• Welsh Farms

Milk is the state drink of Minnesota, Pennsylvania, Maryland, Wisconsin, and South Carolina.

Other milk animals

In addition to cows, the following animals provide milk for dairy products:

• Sheep
• Goats
• Horses
• Donkeys
• Camels (including the South American camelids)
• Yaks
• Water buffalo
• Reindeer

In Russia and Sweden, small moose dairies also exist [10]. Donkey and horse milk have the lowest fat content, while the milk of seals contains more than 50% fat. [11]

Curdling

When raw milk is left standing for a while, it turns sour. This is the result of fermentation: lactic acid bacteria turning the milk sugar into lactic acid. This fermentation process is exploited in the production of various dairy products such as cheese and yogurt.

Pasteurized cow's milk, on the other hand, spoils in a way that makes it unsuitable for consumption, causing it to assume an unpleasant odor and pose a high danger of food poisoning if ingested. The naturally-occurring lactic acid bacteria in raw milk, 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. 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 for many months, unrefrigerated. The most durable form of milk is milk powder which is produced from milk by removing almost all water.

UHT milk is very popular in Europe, whereas in North America, most of the milk sold is pasteurized.

See also

• Almond milk
• Bovine somatotropin
• Babcock test - determines the butterfat content of milk.
• Dairy
• Grain milk
• Milk fetishism
• Rice milk
• Soy milk

References

• Template:Web reference full

External links

• Milking in the early days
• Advances in processing milk
• Year-round grazing of dairy cows in the United States
• Boning Up on Osteoporosis
• Horse milk
• Harvard School of Public Health: Calcium and Milk: describes claims of milk supporters and critics