Powdered milk is a manufactured dairy product made by evaporating milk to dryness. One purpose of drying milk is to preserve it; milk powder has a far longer shelf life than liquid milk and does not need to be refrigerated, due to its low moisture content. Another purpose is to reduce its bulk for economy of transportation. Available as Dry Whole Milk (DWM), it is most commonly produced as Non-Fat Dry Milk (NFDM), also known as Dried Skim Milk (DSM).
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While Marco Polo wrote of Mongolian Tatar troops in the time of Kublai Kahn carrying sun-dried skimmed milk as "a kind of paste"[1], the first usable commercial process to produce dried milk was invented by T.S. Grimwade and patented in 1855[2], though a William Newton had patented a vacuum drying process as early as 1837[3]. Today, powdered milk is usually made by spray drying[4] nonfat skim milk or whole milk. Pasteurized milk is first concentrated in an evaporator to about 50% milk solids. The resulting concentrated milk is sprayed into a heated chamber where the water almost instantly evaporates, leaving fine particles of powdered milk solids.
Alternatively, the milk can be dried by drum drying. Milk is applied as a thin film to the surface of a heated drum, and the dried milk solids are then scraped off. Powdered milk made this way tends to have a cooked flavor, due to caramelization caused by greater heat exposure.
Another process is freeze drying, which preserves many nutrients in milk, compared to drum drying. [5]
The drying method and the heat treatment of the milk as it is processed alters the properties of the milk powder (for example, solubility in cold water, flavor, bulk density).
Powdered milk is frequently used in the manufacture of infant formula, confectionery such as chocolate and caramel, and in recipes for baked goods where adding liquid milk would render the product too thin. Powdered milk is also widely used in various sweets such as the famous Indian milk balls known as gulab jamun and popular Pakistani sweet delicacy (sprinkled with desiccated coconut) known as Chum chum (made with skim milk powder).
Powdered milk is also a common item in UN food aid supplies, fallout shelters, warehouses, and wherever fresh milk is not a viable option. It is widely used in many developing countries because of reduced transport and storage costs (reduced bulk and weight, no refrigerated vehicles). As with other dry foods, it is considered nonperishable, and is favored by survivalists, hikers, and others requiring nonperishable, easy-to-prepare food.
Reconstituting one cup of milk from powdered milk requires one cup of potable water and one-third cup of powdered milk.
Powdered milk is also used in western blots as a blocking buffer to prevent nonspecific protein interactions[5], and is referred to as Blotto.
Milk powders contain all twenty standard amino acids (the building blocks of proteins) and are high in soluble vitamins and minerals[6]. According to USAID[7] the typical average amounts of major nutrients in the unreconstituted milk are (by weight) 36% protein, 52% carbohydrates (predominantly lactose), calcium 1.3%, potassium 1.8%. Their milk powder is fortified with Vitamin A and D, 3000IU and 600IU respectively per 100g. Inappropriate storage conditions (high relative humidity and high ambient temperature) can significantly degrade the nutritive value of milk powder[8].
Commercial milk powders are reported to contain, in general, very low levels of oxysterols (OS)[9]. However, compared to fresh milk (trace levels), powdered milk is higher in oxysterols (oxidized cholesterol), up to 30μg/g, yet significantly lower than powdered eggs (200μg/g)[10]. The OS free radicals have been suspected of being initiators of atherosclerotic plaques[11].
In the 2008 baby milk scandal in China, melamine adulterant was found in Sanlu infant formula, added to fool tests into reporting higher protein content. Thousands became ill and some children died after consuming the product.