Yogurt, Cheese, and Other Fermented Milk Products
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Fermented milk products, including yogurt and cheese, are formed when bacteria break down lactose to produce lactic acid, which sours the milk. Yogurt is usually made from milk that has been fortified by the addition of nonfat powdered milk to improve its texture and taste. The fortified milk is pasteurized at a very high temperature and homogenized. A culture containing the bacteria Streptococcus thermophilus and Lactobacillus bulgaricus, and sometimes Lactobacillus acidophilus, is then added. The two most popular types of yogurt sold are Swiss-style, with added fruit mixed throughout, and sundae-style, with fruit on the top or bottom.
Cultured buttermilk and sour cream, like yogurt, are produced by the breakdown of lactose by bacteria. Cultured buttermilk used to be made from buttermilk, but is now more commonly made from skim milk. Sour cream is made from cream. Both have a tangy, sour taste imparted by lactic acid.
Cheese making is a complex process, with each of the more than 400 varieties of cheeses differing in the details of the process. However, most cheese making follows the same basic steps. Bacteria are introduced into milk that consume lactose and produce lactic acid. Cheeses are allowed to ferment longer than yogurt, buttermilk, and sour cream, which gives the bacteria time to also digest some of the fat and protein present. The waste products produced by bacteria from digesting fats and proteins provide cheeses with their distinctive and stronger flavors. Acidification of milk or the addition of the enzyme rennin precipitates moist lumps of protein called curds. The curds contain all of the milk’s protein and most of the fat, minerals, and vitamins. The residual thin liquid is known as whey. The curds are salted (for taste) and pressed into shape, which eliminates more of the whey. The pressed curd is then cured under controlled temperature and humidity for varying lengths of time to produce cheese.
Fermented milk products, including yogurt and cheese, are formed when bacteria break down lactose to produce lactic acid, which sours the milk. Yogurt is usually made from milk that has been fortified by the addition of nonfat powdered milk to improve its texture and taste. The fortified milk is pasteurized at a very high temperature and homogenized. A culture containing the bacteria Streptococcus thermophilus and Lactobacillus bulgaricus, and sometimes Lactobacillus acidophilus, is then added. The two most popular types of yogurt sold are Swiss-style, with added fruit mixed throughout, and sundae-style, with fruit on the top or bottom.
Cultured buttermilk and sour cream, like yogurt, are produced by the breakdown of lactose by bacteria. Cultured buttermilk used to be made from buttermilk, but is now more commonly made from skim milk. Sour cream is made from cream. Both have a tangy, sour taste imparted by lactic acid.
Cheese making is a complex process, with each of the more than 400 varieties of cheeses differing in the details of the process. However, most cheese making follows the same basic steps. Bacteria are introduced into milk that consume lactose and produce lactic acid. Cheeses are allowed to ferment longer than yogurt, buttermilk, and sour cream, which gives the bacteria time to also digest some of the fat and protein present. The waste products produced by bacteria from digesting fats and proteins provide cheeses with their distinctive and stronger flavors. Acidification of milk or the addition of the enzyme rennin precipitates moist lumps of protein called curds. The curds contain all of the milk’s protein and most of the fat, minerals, and vitamins. The residual thin liquid is known as whey. The curds are salted (for taste) and pressed into shape, which eliminates more of the whey. The pressed curd is then cured under controlled temperature and humidity for varying lengths of time to produce cheese.
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