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, lactose, 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 (Keralan), and Polynesian cuisine.

* a non-animal substitute such as soya milk, rice milk, and almond milk.

Human milk is often fed to infants through breastfeeding, either directly or by the female expressing her milk to be saved and fed later. As colostrum, it carries the mother's antibodies and intestinal bacteria 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, in contrast, 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.

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 breeds of cattle produce milk that is significantly different from that of others as do different mammals' from others. 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.

Milk has also been linked in a small number of studies to osteoporosis, cancer, heart disease, obesity and high blood pressure yet countries where dairy products are plentiful and cheap, such as New Zealand and Australia, have no particular indications of those diseases.

Cow's milk

Cow's milk is produced on an industrial scale for human consumption.

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 a disgusting odor, which alone may induce vomiting in sensitive persons, 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. 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. The most durable form of milk is milk powder which is produced from milk by removing almost all water.

Distribution

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 round his local milk round 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 and 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. But few people have ever tasted fresh, unprocessed, milk straight from the cow.

In the United States, milk is commonly sold in gallon, half-gallon and quart containers (U.S. customary units). The U.S. single serving size is usually the half-pint. In Europe, metric sizes of 500 millilitres, 1 litre, 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)).

In 1856 Gail Borden was granted a patent for his method of condensing, or removing the bulk of the water from, milk. Prior to that development, milk could only be kept fresh for a few days and so was only available in the immediate vicinity of a cow. While returning from a trip to England in 1851, Borden was devastated by the death of several children, apparently due to poor milk from shipboard cows. Without benefit of more than a year of school, following a wake of failures both of his own and others, Borden was inspired by the vacuum pan he had seen used by Sharkers to condense fruit juice and was at last able to reduce milk without scorching or curdling it. Even then, his first two factories failed and only the third, in Wassaic, New York, produced a usable milk derivative; long lasting without refigeration.

Probably of equal importance for the future of milk, was Borden's requirements for farmers who wanted to sell him raw milk: They were required to wash udders before milking, keep barns swept clean, and scald and dry their strainers morning and night. By 1858 Borden's milk had gained a reputation for purity, durability and economy. The federal government ordered condensed milk as a field ration during the civil war and soldiers returning home spread the word. By the late 1860s milk was a major industry.

Ethical issues

Many people concerned about animal welfare (especially vegans) do not drink milk. An increasing number of dairy cows are being raised on factory farms, which some people consider cruel. On many farms, the calves are separated from their mothers within days of birth to prevent the calf from drinking the milk so that humans can drink it instead. Some of the calves born by dairy cows are raised in crates for veal and are slaughtered three to eighteen weeks later. On many farms, once a dairy cow's milk production decreases, she is also slaughtered at an age that is a fraction of her natural lifespan. For these reasons, either in an attempt to reduce animal suffering or to prevent animals from being killed, some people choose to not consume milk. Some also object to drinking milk for environmental reasons.