From a Squirt of Milk to a Spoonful of Powder
BY AWAKE! CORRESPONDENT IN NEW ZEALAND
FOR thousands of years and in practically every nation, milk has been a staple in the human diet. Milk, of course, comes from the mammary glands of females and is a complete food for their young. Unlike other creatures, however, humans have obtained this most nourishing of foods from a variety of mammals—in particular, from cows, camels, goats, llamas, reindeer, sheep, and water buffalo. Besides drinking milk straight, people also enjoy its many derivatives, among the more popular being butter, cheese, yogurt, and ice cream.
One of the more common milks, cow’s milk, is essentially an emulsion of 87 percent water and 13 percent solids. These solids include carbohydrates, proteins, fats, vitamins, and such minerals as calcium—important for bone growth and maintenance. Cows, incidentally, do not produce the richest milk. Of the animals listed above, that distinction goes to the reindeer, whose highly nutritious milk is about 37 percent solids!
Regardless of the source, milk does not keep for long unless refrigerated. A popular solution to this problem is powdered milk. But how do you turn milk into powder? Let’s pay a short visit to a modern milk processing plant at Waikato, New Zealand. This plant is one of the largest of its type in the world and daily produces 400 tons of complex milk powders for the global food industry.
From Liquid to Powder
Each day, a fleet of trucks with polished-steel trailer tanks brings fresh milk from New Zealand’s dairies to the plant, where the milk is kept fresh in insulated silos. From there, the milk moves into standardization separators, where it is separated into skim milk and cream and then remixed in specific quantities to give the end product the correct standard, or consistency. From the separators it goes to buffer storage before being made into milk powder.
Following pasteurization, the milk is boiled under vacuum. Why under vacuum? This ensures that the milk boils at a much lower temperature than normal, minimizing heat damage. When this stage of evaporation is complete, the solid concentration of the milk is approximately 48 percent. This concentrated product is now ready for the final process—drying.
The drying process begins with the concentrated milk being piped to the top of a multistory stainless steel dryer, where it is sprayed into heated air inside the dryer. The milk’s moisture content now falls to 6 percent, and it becomes a powder. One more stage reduces the moisture to 3 percent, after which the powder is gently cooled in preparation for packaging and shipping. The whole process is rigorously executed with minimal loss of the milk’s nutritional value and goodness.
You might live in an area where fresh milk is readily available. But many people live in isolated areas where fresh milk is hard to obtain and is expensive. Thanks to the marvel of powdered milk, their problems are solved. They just mix a few spoonfuls of powder with water, and the reconstituted milk, though not as tasty as fresh milk, does the job admirably.
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What Are Pasteurization and Homogenization?
Named after French scientist Louis Pasteur, pasteurization involves heating milk for a specified time and then cooling it quickly. This process kills harmful bacteria and thus extends the shelf life of milk. However, not all bacteria are killed, so milk products still have a limited shelf life. When properly refrigerated, high-quality pasteurized milk has a shelf life of about 14 days.
Homogenization physically changes the fat or cream globules in milk so that they do not float to the top of the milk and form a layer of cream. Homogenizers break up fat globules into units small enough to remain in suspension, giving milk a rich, even consistency.
By courtesy of U.S. National Library of Medicine
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This multistory dryer can dry more than nine tons of milk powder each hour