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What is milk?
Milk is a nutrient-rich liquid produced by the mammary glands of female mammals to feed their young after birth. Humans also consume milk from domesticated animals or process it into dairy products like butter, cheese, ice cream, and yogurt.
Cow's milk is the most common type consumed worldwide, but milk from sheep and goats is also consumed in some areas. Milk consists of fat and protein in water, along with sugar, minerals, and vitamins. Milk's mineral content includes calcium and phosphorus, and it also contains B vitamins.
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Where does milk come from?
Milk is a nutrient-rich liquid produced by the mammary glands of female mammals to nourish their young after birth. For human consumption, the milk of domesticated animals like cows, sheep, goats, buffalo, and camels is used.
After a cow gives birth, milk production begins and can be maintained by regular milking. On dairy farms, milking is typically done two or three times a day using machines. The collected raw milk is then transported to processing plants where it undergoes several processes including pasteurization, homogenization, and separation to ensure safety and quality.
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Which animals produce milk for humans to drink?
Humans consume milk from various domesticated animals, with cow's milk being the most common worldwide. Other significant sources include water buffalo, especially in Asia, and goats, particularly in the Mediterranean. Less common sources are sheep, camels, yaks, horses, reindeer, and donkeys. Different breeds of dairy cattle, such as Ayrshire, Brown Swiss, Guernsey, Holstein-Friesian, and Jersey, are known for their milk production volume and composition.
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What nutrients are found in milk?
Milk contains approximately 12 to 13 percent total solids, and it contains water, fat, protein, carbohydrates (lactose), and minerals (ash). Milk also contains micronutrients such as vitamins, essential amino acids, and trace minerals; more than 250 chemical compounds have been identified in milk. Milk is an excellent source of calcium and phosphorus and provides B vitamins, especially riboflavin (B2). It also contains trace amounts of potassium, chloride, sodium, magnesium, sulfur, copper, iodine, and iron.
For older adults, consuming dairy helps maintain strong bones and provides vital nutrients, including calcium, potassium, and vitamin D. Skim milk and low-fat milk are commonly fortified with the fat-soluble vitamins A and D.
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How is milk processed before it is sold in stores?
Before milk is sold in stores, it undergoes several key processes. Initially, the raw milk is tested for various factors like odor, appearance, temperature, bacteria levels, and drug residues. If approved, it's stored in refrigerated tanks. Next, pasteurization occurs, where the milk is heated to a specific temperature to eliminate harmful bacteria. Following this, homogenization breaks down fat globules for uniform consistency. Finally, the milk is packaged into paper cartons or plastic jugs and marked with a date indicating its freshness.
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Why do some people have trouble drinking milk?
Some people have trouble drinking milk due to lactose intolerance, a condition characterized by the inability to digest lactose, the main sugar in dairy products. This is usually caused by a deficiency of lactase, the enzyme that breaks down lactose in the small intestine.
Lactose intolerance can be congenital (present at birth), primary (develops over time), or secondary (due to intestinal lining damage). Symptoms include bloating, cramping, abdominal pain, diarrhea, and flatulence.
The incidence of primary lactose intolerance varies among different populations, with 75 to 90 percent of Native Americans, Blacks, Latinos, Asians, Mediterraneans, and Jews affected, compared to only about 5 percent of northern and central European descendants. This is likely due to a genetic mutation that leads to lactase persistence.
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milk, liquid secreted by the mammary glands of female mammals to nourish their young for a period beginning immediately after birth. The milk of domesticated animals is also an important food source for humans, either as a fresh fluid or processed into a number of dairy products such as butter and cheese.
A brief treatment of milk follows. For full treatment, see dairy product.
Almost all the milk now consumed in Western countries is from the cow, and milk and milk products have become important articles of commerce. Other important sources of milk are the sheep and goat, which are especially important in southern Europe and the Mediterranean area; the water buffalo, which is widely domesticated in Asia; and the camel, which is important in the Middle East and North Africa.
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Milk is essentially an emulsion of fat and protein in water, along with dissolved sugar (carbohydrate), minerals, and vitamins. These constituents are present in the milk of all mammals, though their proportions differ from one species to another and within species. (See Table.) The milk of each species seems to be a complete food for its own young for a considerable time after birth. In the stomachs of the young, milk is converted to a soft curd that encloses globules of fat, enabling digestion to proceed smoothly without the disturbance often caused by fatty food. Lactose, or milk sugar, is broken down into simpler digestible sugars by the enzyme lactase, which is produced in the intestine of infants. Infants who do not produce lactase develop lactose intolerance, a condition in which a variety of gastrointestinal problems arise. Lactose intolerance also commonly develops after weaning or with advancing age, when many individuals cease producing lactase.
| source | energy (kcal) | fat (g) | cholesterol (mg) | protein (g) | calcium (mg) | phosphorus (mg) | carbohydrate (g) |
|---|---|---|---|---|---|---|---|
| Source: U.S. Department of Agriculture, Composition of Foods, Agriculture Handbook no. 8-1. | |||||||
| human | 70 | 4.38 | 14 | 1.03 | 32 | 14 | 6.89 |
| cow | 61 | 3.34 | 14 | 3.29 | 119 | 93 | 4.66 |
| goat | 69 | 4.14 | 11 | 3.56 | 134 | 111 | 4.45 |
| sheep | 108 | 7.00 | — | 5.98 | 193 | 158 | 5.36 |
| water buffalo | 97 | 6.89 | 19 | 3.75 | 169 | 117 | 5.18 |
Milk protein is of high nutritional value because it contains all the essential amino acids—i.e., those which infants cannot synthesize in the necessary quantities. Milk’s mineral content includes calcium and phosphorus in quantities sufficient for normal skeletal development, but little iron. Milk contains B vitamins as well as small amounts of vitamins C and D. Commercial cow’s milk is commonly enriched with vitamins D and A before sale.
Microorganisms contained in raw (unheated) milk or picked up from the environment will quickly sour and curdle the milk. Cooling to slightly above its freezing point keeps milk palatable for a longer time by reducing the multiplication of spoilage bacteria and the chemical changes that they induce.
Many countries have laws requiring that milk be pasteurized as a protection against pathogenic (disease-causing) organisms. Pasteurization is a partial sterilization accomplished by raising the milk to a temperature high enough to destroy pathogenic bacteria and a large proportion of those causing spoilage. Pasteurized milk that is kept refrigerated in closed containers will remain consumable for approximately 14 days.
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Milk fat, being less dense than other milk components, can be efficiently removed in a cream separator by centrifugation, yielding low-fat milk and skim milk. Low-fat milk contains 1–2 percent fat, while skim milk contains less than 0.5 percent fat.
Much of the milk sold as a beverage has undergone homogenization, a process in which the milk is forced under high pressure through small openings to distribute the fat evenly throughout the milk.