Milk

I

Introduction

Milk, highly nutritious, versatile food. People enjoy drinking milk in its natural form and also use it to make a wide range of food products, including cream, butter, yogurt, cheese, and ice cream.

Female mammals produce milk to feed their newly born young. Milk is produced in the mother’s mammary glands, which are found, for example, in the breasts of humans or the udders of cows, sheep, or goats. Each species of mammal produces milk with a unique composition designed to meet the specific needs of its infants. For instance, the milk of animals that need to develop a thick layer of insulating fat, such as seals, has a high fat content. The milk of animals that grow rapidly, such as cows, which double their birth weight in 50 days, is rich in protein and minerals.

Humans drink the milk produced from a variety of domesticated mammals, including cows, goats, sheep, camels, reindeer, buffaloes, and llama. By far the vast majority of milk used for commercial production and consumption is from cows. This article focuses on the nutritional value and production of cow milk. For information on the branch of agriculture concerned with the raising of cows (or other domesticated mammals) for the purpose of collecting their milk, see also Dairy Farming.

II

Nutritional Value of Milk

Most milk is composed of 80 to 90 percent water. The remaining 10 percent consists of an abundance of the major nutrients needed by the body for good health, including fats, carbohydrates, proteins, minerals, and vitamins.

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Cow milk typically contains about 3.5 to 5 percent fat, which is dispersed throughout the milk in globules. In addition to providing milk’s characteristic taste and texture, fat supplies vitamins A, D, E, and K, as well as certain fatty acids that the body cannot produce on its own.

Lactose, a kind of sugar found only in milk, gives milk its sweet taste. Making up about 5 percent of milk’s content, lactose is a carbohydrate that is broken down by the body to supply energy. Infants digest lactose easily, but many adults, especially those of Asian and African ancestry, have lost some of their ability to digest this sugar. When these adults drink milk, they often suffer gastric distress and diarrhea.

The most important protein in milk is casein, accounting for 80 percent of milk protein. Casein is a complete protein, meaning that it contains all of the essential amino acids, which the body cannot manufacture on its own. Casein molecules and globules of fat deflect light rays passing through milk, giving milk its opalescent appearance. Other proteins present in milk include albumin and globulin.

Milk contains many minerals, the most abundant of which are calcium and phosphorus, as well as smaller amounts of potassium, sodium, sulfur, aluminum, copper, iodine, manganese, and zinc. Milk is perhaps the best dietary source of calcium—one liter (about 1 qt) of milk supplies as much calcium as 21 eggs, 12 kg (26 lb) of lean beef, or 2.2 kg (5 lb) of whole wheat bread. Milk is an excellent source of vitamins A and B₂ (see riboflavin). All other vitamins are present also, but in lower doses. Vitamin D is typically added to commercially sold milk. Vitamin A, which is found in the globules of fat, is removed when fat is skimmed away to make low-fat or skim milk. Generally, vitamin A is replaced during the production of commercially sold low-fat milk.

III

Human Breast Milk

Human milk provides distinct advantages over formula or cow milk for human infants. Not only is breast milk’s nutritional composition uniquely designed for the needs of human babies, but it also contains antibodies from the mother’s immune system that help the infant fight off infections and diseases. During the first few days after giving birth, a mother releases colostrum, a yellowish liquid that contains less fat and lactose and more protein and antibodies than regular breast milk. After about three or four days, colostrum is replaced by a bluish-white milk that is higher in fats and carbohydrates, reflecting the energy needs of a growing baby (see Breast-feeding).

IV

Milk Products

Milk in its natural form, directly from a cow, is called raw milk. It is an extremely versatile product from which a myriad of commercial products are derived.

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