Milk is an opaque white liquid produced by the mammary glands of mammals. It provides the primary source of nutrition for young mammals 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. 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. Cow's milk has a pH ranging from 6.4 to 6.8, making it slightly acidic.
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.
In almost all mammals, milk is fed to infants through breastfeeding, either directly or by expressing the milk to be stored and consumed later. Some cultures, historically or currently, continue to use breast milk to feed their children until they are 7 years old.
In many cultures of the world, especially the Western world, humans continue to consume milk beyond infancy, using the milk of other animals (especially cattle, goats and sheep) as a food product. For millennia, cow's milk has been processed into dairy products such as cream, butter, yogurt, kefir, ice cream, and especially the more durable and easily transportable product, cheese. Modern industrial processes produce casein, whey protein, lactose, condensed milk, powdered milk, and many other food-additive and industrial products.
Humans are an exception in the natural world for consuming milk past infancy, despite the fact that more than 75% of adult humans show some degree (some as little as 5%) of lactose intolerance, a characteristic that is more prevalent among individuals of African or Asian descent. The sugar lactose is found only in milk, forsythia flowers, and a few tropical shrubs. The enzyme needed to digest lactose, lactase, reaches its highest levels in the small intestines after birth and then begins a slow decline unless milk is consumed regularly. On the other hand, those groups that do continue to tolerate milk often have exercised great creativity in using the milk of domesticated ungulates, not only of cattle, but also sheep, goats, yaks, water buffalo, horses, and camels. The largest producer and consumer of cattle and buffalo milk in the world is India.
|Country||Milk (litres)||Cheese (kg)||Butter (kg)|
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 secreted by glands in the mucosa of their upper digestive tract which pigeons feed their young is called crop milk though it bears little resemblance to mammalian milk.
In the United States, there are two grades of milk, with Grade A primarily used for direct sales and consumption in stores, and Grade B used for indirect consumption, such as in cheesemaking or other processing.
The differences between the two grades are defined in the Wisconsin administrative code for Argiculture, Trade, and Consumer Protection, chapter 60. Grade B generally refers to milk that is cooled in milk cans, which are immersed in a bath of cold flowing water, typically drawn up from an underground water well rather than using mechanical refrigeration.
Milk glands are highly specialized sweat glands. It has been suggested that the original function of lactation (milk production) was to keep eggs moist. Much of the argument is based on monotremes (egg-laying mammals):
Animal milk is first known to have been used as human food during the Secondary Products Revolution, around 5000BC. It is assumed that when animals such as cattle were first domesticated, it was only for purposes of meat. Cow's milk was first used as human food in the Middle East. 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 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.
Milk byproducts found inside stone age pottery from Turkey indicate processed milk was consumed in 6500 BC some thousands of years before the ability for adult humans to digest unprocessed milk had evolved.
DNA evidence extracted from Neolithic skeletons indicates that a thousand years later in 5500 BC people in Northern Europe were like all other peoples of the time and were still lactose intolerant. Earthenware vessels found in England from a thousand years after this in 4500 BC contain milk byproducts indicating milk was used in some form although perhaps not drunk directly.
Milk was first delivered in bottles on January 11, 1878. The day is now remembered as Milk Day and is celebrated annually. The town of Harvard, Illinois also celebrates milk in the summer with a festival known as "Milk Days". Theirs is a different tradition meant to celebrate dairy farmers in the "Milk Capital of the World."
According to the National Bison Association, American Bison (also called American buffalo) are not milked commercially. However, various sources report cows resulting from cross-breeding bison and domestic cattle are good milk producers, both during the European settlement of North America and during the development of commercial Beefalo in the 1970s and 1980s.
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.
In the Western world today, cow's milk is produced on an industrial scale, and 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. Dairy cattle such as the Holstein have been specially bred for increased milk production. 90% of the dairy cows in the United States and 85% in Great Britain are Holsteins. Other dairy cows in the United States include Ayrshire, Brown Swiss, Guernsey, Jersey, and Milking Shorthorn (Dairy Shorthorn). The largest producers of dairy products and milk today are India followed by the United States, Germany, and Pakistan.
Increasing affluence in developing countries, as well as increased promotion of milk and milk products, has led to a rise in milk consumption in developing countries in recent years. In turn, the opportunities presented by these growing markets have attracted investment by multinational dairy firms. Nevertheless, in many countries production remains on a small-scale and presents significant opportunities for diversification of income sources by small farmers. Local milk collection centers, where milk is collected and chilled prior to being transferred to urban dairies, are a good example of where farmers have been able to work on a cooperative basis, particularly in countries such as India.
This table below shows the numbers of water buffalo milk production. Cattle milk is produced in a much wider range.
|People's Republic of China||2,900,000||FAO estimate|
It was reported in 2007 that with increased worldwide 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.
Milk is an emulsion or colloid 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.
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, k-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.
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 (such as Guernsey and Jersey cattle) 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. 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.
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.
The carbohydrate lactose gives milk its sweet taste and contributes about 40% of whole cow's 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. Other components found in raw cow's milk are living white blood cells, Mammary-gland cells, various bacteria, and a large number of active enzymes.
In most Western countries, a centralized dairy facility processes milk and products obtained from milk (dairy products), such as cream, butter, and cheese. In the U.S., 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 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.
A newer process, Ultra Pasteurization or ultra-high temperature treatment (UHT), heats the milk to a higher temperature for a shorter time. This extends its shelf life and allows the milk to be stored unrefrigerated because of the longer lasting sterilization effect.
Microfiltration is a process that partially replaces pasteurization and produces milk with fewer microorganisms and longer shelf life without a change in the taste of the milk. In this process, cream is separated from the whey and is pasteurized in the usual way, but the whey is forced through ceramic microfilters that trap 99.9% of microorganisms in the milk (as compared to 95% killing of microorganisms in conventional pasteurization). The whey is then recombined with the pasteurized cream to reconstitute the original milk composition.
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's 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. 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.
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 flavors. Creamline, or cream-top, milk is unhomogenized; it may or may not have been pasteurized. Milk which has undergone high-pressure homogenization, sometimes labeled as "ultra-homogenized," has a longer shelf life than milk which has undergone ordinary homogenization at lower pressures. Homogenized milk may be more digestible than unhomogenized milk.
Kurt A. Oster, M.D., who worked in the 1960s through the 1980s, suggested a link between homogenized milk and arterosclerosis, due to damage to plasmalogen as a result of the release of bovine xanthine oxidase (BXO) from the milk fat globular membrane (MFGM) during homogenization. However, Oster's hypothesis has been widely criticized and has not been generally accepted by the scientific community. No link has been found between arterosclerosis and milk consumption.
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. For example:
Donkey and horse milk have the lowest fat content, while the milk of seals and whales can contain more than 50% fat. High fat content is not unique to aquatic mammals, as guinea pig milk has an average fat content of 46%.
|Fatty acids saturated||g||2.4||2.3||3.8||4.2|
|Mono-unsaturated fatty acids||g||1.1||0.8||1.5||1.7|
|Polyunsaturated ffatty acids||g||0.1||0.1||0.3||0.2|
These compositions vary by breed, animal, and point in the lactation period.
|Cow breed||Approximate percentage|
The protein range for these four breeds is 3.3% to 3.9%, while the lactose range is 4.7% to 4.9%.
Milk fat percentages can be manipulated by dairy farmers' diet formulation strategies. Mastitis infection can cause fat levels to decline.
|Nutritional value per 100 g (3.5 oz)|
|Energy||252 kJ (60 kcal)|
|Aspartic acid||0.237 g|
|Glutamic acid||0.648 g|
|Vitamin A equiv.||28 μg (3%)|
|Thiamine (Vit. B1)||0.044 mg (3%)|
|Riboflavin (Vit. B2)||0.183 mg (12%)|
|Vitamin B12||0.44 μg (18%)|
|Vitamin D||40 IU (10%)|
|Calcium||113 mg (11%)|
|Magnesium||10 mg (3%)|
|Potassium||143 mg (3%)|
|100 ml corresponds to 103 g.
Percentages are relative to US recommendations for adults.
Source: USDA Nutrient database
Processed milk began containing differing amounts of fat during the 1950s. 1 cup (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, milk contains 8 grams of protein, and a number of other nutrients (either naturally or through fortification) including:
The amount of calcium from milk that is absorbed by the human body is disputed. Calcium from dairy products has a greater bioavailability than calcium from certain vegetables, such as spinach, that contain high levels of calcium-chelating agents, but a similar or lesser bioavailability than calcium from low-oxalate vegetables such as kale, broccoli, or other vegetables in the Brassica genus.
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. One 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. Milk is a source of Conjugated linoleic acid.
Milk appears to be effective at promoting muscle growth.
Lactose, the disaccharide sugar component of all milk must be cleaved in the small intestine by the enzyme lactase in order for its constituents (galactose and glucose) to be absorbed. The production of this enzyme declines significantly after weaning in all mammals. Consequently, many humans become unable to properly digest lactose as they mature. There is a great deal of variance, with some individuals reacting badly to even small amounts of lactose, some able to consume moderate quantities, and some able to consume large quantities of milk and other dairy products without problems. When an individual consumes milk without producing sufficient lactase, they may suffer 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, a process known as anaerobic respiration.
It is estimated that 30 to 50 million Americans are lactose intolerant, including 75 percent of Native Americans and African-Americans, and 90 percent of Asian Americans. Lactose intolerance is less common among those descended from northern Europeans.
Lactose intolerance is a natural process and there is no reliable way to prevent or reverse it. Lactase is readily available in pill form, and many individuals can use it to briefly increase their tolerance for dairy products.
Other studies suggest that milk consumption may increase the risk of suffering from certain health problems. Cow's 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. Milk contains casein, a substance that breaks down in the human stomach to produce casomorphin, an opioid peptide. In the early 1990s it was hypothesized that casomorphin can cause or aggravate autism, and casein-free diets are widely promoted. Studies supporting these claims have had significant flaws, and the data are inadequate to guide autism treatment recommendations. Studies described in the book The China Study note a correlation between casein intake and the promotion of cancer cell growth when exposed to carcinogens. However other studies have shown whey protein offers a protective effect against colon cancer.
A study demonstrated that men who drink a large amount of milk and consume dairy products were at a slightly increased risk of developing Parkinson's disease; the effect for women was smaller. The reason behind this is not fully understood, and it also remains unclear why there is less of a risk for women. 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, i.e., low-fat milk and other dairy to which vitamin A palmitate has been added. 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. Medical studies have also shown a possible link between milk consumption and the exacerbation of diseases such as Crohn's disease, Hirschsprung's disease–mimicking symptoms in babies with existing cow's milk allergies, and the aggravation of Behçet's disease.
Since November 1993, with FDA approval, Monsanto has been selling recombinant bovine somatotropin (rbST), also called rBGH, to dairy farmers. Cows produce bovine growth hormone naturally, but some producers administer an additional recombinant version of BGH which is produced through a genetically-engineered E. coli because it increases milk production. Bovine growth horome also stimulates liver production of insulin-like growth factor 1 (IGF1). If rbST-treated cows produced milk with higher levels of IGF1 this would be of medical concern, because IGF1 stimulates cancer growth in humans. Elevated levels of IGF1 in human blood has been linked to increased rates of breast, colon, and prostate cancer. Monsanto has stated that both of these compounds are harmless given the levels found in milk and the effects of pasteurization. However Monsanto's own tests, conducted in 1987, demonstrated that statistically significant growth stimulating effects were induced in organs of adult rats by feeding IGF-1 at low dose levels for only two weeks. "Drinking rBGH milk would thus be expected to significantly increase IGF-1 blood levels and consequently to increase risks of developing breast cancer and promoting its invasiveness."
The EU has recommended against Monsanto milk 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." Milk from cows given rBST may be sold in the United States, and the FDA stated that no significant difference has been shown between milk derived from rBST-treated and that from non-rBST-treated cows. Milk that advertises that it comes from cows not treated with rBST is required to state this finding on its label.
Cows receiving rBGH supplements may more frequently contract an udder infection known as mastitis. Problems with mastitis have led to Canada, Australia, New Zealand, and Japan banning milk from rBST treated cows. Mastitis, among other diseases, may be responsible for the fact that levels of white blood cells in milk vary naturally.
Vegans and some other vegetarians do not consume milk for a variety of reasons. They may object to features of dairy farming including the necessity of killing almost all the male offspring of dairy cows (either by disposal soon after birth, for veal production, or for beef), the routine separation of mother and calf soon after birth, other perceived inhumane treatment of dairy cattle, and culling of cows after their productive lives.
Milk products are sold in a number of varieties based on types/degrees of
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.
Reduced fat milks often have added vitamin A palmitate 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.
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"). 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.
Milk often has flavoring added to it for better taste or as a means of improving sales. Chocolate milk has been sold for many years and has been followed more recently by such other flavors as strawberry and banana.
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.
In the UK, milk can be delivered daily by a milkman who travels his local milk round (route) using a milk float (often battery powered) 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 cheque; 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 used by people up and down the country.
In Australia and New Zealand, prior to "metrification", milk was generally distributed in 1 pint (568ml) glass bottles. In Australia there was a government funded "free milk for school children" program, and milk was distributed at morning recess in 1/3 pint bottles. With the conversion to metric measures, the milk industry were concerned that the replacement of the pint bottles with 500ml bottles would result in a 13.6% drop in milk consumption. Hence, all pint bottles were recalled and replaced by 600ml bottles. With time, due to the steadily increasing cost of collecting, transporting, storing and cleaning glass bottles, they were replaced by cardboard cartons. A number of designs were used, including a tetrahedron which could be close-packed without waste space, and could not be knocked over accidentally. (slogan: No more crying over spilt milk.) However, the industry eventually settled on a design similar to that used in the United States. Milk is now availability in a variety of sizes in cardboard cartons (250ml, 375ml, 600ml, 1 litre and 1.5 litres) and plastic bottles (1 in NZ , 1.1 in Australia, 2 and 3 litres). A significant addition to the marketplace has been "long life" milk (UHT), generally available in 1 and 2 litre rectangular cardboard cartons. In urban and suburban areas where there is sufficient demand, home delivery is still available, though in suburban areas this is often 3 times per week rather than daily. Another significant and popular addition to the marketplace has been flavoured milks - for example, as mentioned above, Farmers Union Iced Coffee outsells Coca-Cola in South Australia.
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, glass milk bottles have been mostly replaced with milk cartons (tall paper boxes with a square cross-section and a peaked top that can be folded outward upon opening to form a spout) and plastic jugs. Gallons of milk are almost always sold in jugs, while half-gallons and quarts may be found in both paper cartons and plastic jugs, and smaller sizes are almost always in cartons. Recently, milk has been sold in smaller resealable bottles made to fit in automobile cup holders. These individual serving sizes are also sold in flavored varieties.
The half-pint milk carton is the traditional unit as a component of school lunches.
In Pakistan, milk is supplied in jugs. Milk has been a staple food, especially among the pastoral tribes in this country.
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. It is more typically sold unrefrigerated on the shelves in Europe and Latin America than in the United States. In Australia it is generally sold unrefrigerated, though some supermarkets also keep small quantities refrigerated.
Glass milk containers are now rare. Most people purchase milk in bags, plastic bottles, or plastic-coated paper cartons. Ultraviolet (UV) light from fluorescent lighting can alter the flavor of 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:
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.
When raw milk is left standing for a while, it turns "sour". This is the result of fermentation, where lactic acid bacteria ferment the lactose inside the milk into lactic acid. Prolonged fermentation may render the milk unpleasant to consume. This fermentation process is exploited by the introduction of bacterial cultures (e.g. Lactobacilli sp., Streptococcus sp., Leuconostoc sp., etc) to produce a variety of fermented milk products. The reduced pH from lactic acid accumulation denatures proteins and caused the milk to undergo a variety of different transformations in appearance and texture, ranging from an aggregate to smooth consistency. Some of these products include sour cream, yoghurt, cheese, buttermilk, viili, kefir and kumis. See Dairy product for more information.
Pasteurization of cow's milk initially destroys any potential pathogens and increases the shelf-life , but eventually results in spoilage that makes it unsuitable for consumption. This causes it to assume an unpleasant odor, and the milk is deemed non-consumable due to unpleasant taste and an increased risk of food poisoning. In raw milk, the presence of lactic acid-producing bacteria, under suitable conditions, ferments the lactose present to lactic acid. The increasing acidity in turn prevents the growth of other organisms, or slows their growth significantly. During pasteurization however, these lactic acid bacteria are mostly destroyed.
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. 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 five percent in both drum and spray dried milk powder.
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.
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.
The verb, "to milk" something is often used in the vernacular of many English-speaking countries as a synonym for extortion or, in less loaded terms, taking advantage of a situation where one has another person at a disadvantage, as in 'milking the situation'.
The word milk has had many slang meanings over time. In the early 17th century the word was used to mean semen, or vaginal secretions, or to masturbate oneself or someone else. In the 19th century, milk was used to describe a cheap alcoholic drink made from methylated spirits mixed with water. The word was also used to mean defraud, to be idle, to intercept telegrams addressed to someone else, and a weakling or 'milksop'. In the mid 1930s, the word was used in Australia meaning to siphon gas from a car.
Besides serving as a beverage or source of food, milk has been described as used by farmers and gardeners as an organic fungicide and foliage fertilizer. Diluted milk solutions have been demonstrated to provide an effective method of preventing powdery mildew on grape vines, while showing it is unlikely to harm the plant.
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Milk is a white liquid produced by mammals, for example cows, dogs, and humans. It is made in the mammary glands (breasts, udders, or teats) of female mammals. Because newborn babies have no teeth, they must be fed milk before they can eat solid food. Milk contains many nutrients to help babies grow and be healthy.
If milk is not kept cool in a refrigerator, it will spoil and become sour after some time. When milk is warmed, it turns sour. Fermentation makes this happen. Lactic acid bacteria changes the milk sugar into lactic acid. Fermentation is used when making dairy products.
Milk is often pasteurised before humans drink it, or is made into dairy products like cream, butter, yoghurt, ice cream, gelato, or cheese. Pasteurised cows' milk will turn sour if it is not kept in a refrigerator. Milk should be stored between 1° and 4° Celsius. If milk is treated with ultra-high temperatures (UHT), it will last longer before spoiling. This means it does not have to be put in the refrigerator until it is opened.
Milk contains a chemical called lactose. Babies make an enzyme called lactase inside their bodies. Adults make less lactase. If they do not have enough, they may not be able to digest lactose anymore. This problem is called lactose intolerance and it affects many adults. There are many medicines that help adults digest lactose. Many lactose-intolerant people drink soy milk instead of animal milk, because it does not contain lactose. Soy milk is similar to animal milk, but it is made from soybeans.
Coconut milk looks similar to real milk, but it does not have as many nutrients. It is made by removing the white "meat" from a coconut, pressing or squeezing the "meat", then adding water. It is sometimes used in cooking, for example, in Thai curry. Coconut cream is a thicker version of coconut milk which contains added sugar.
Milk forms an important part of a person's daily balanced diet. It contains a lot of calcium that helps bones and teeth to grow stronger. Also, milk provides the body with high quality proteins, and helps in meeting the body's requirement for vitamins. One glass of milk gives about 44% to the daily-recommended vitamins intake. Some kind of milks, though, do not have good calcium. These kind of milk products include cream, cottage cheese, ricotta cheese, and cream cheese.
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