Yogurt
Yogurt is a dairy product made by curdling milk through bacterial fermentation. Any sort of milk may be used to make yogurt, but modern production is dominated by cow's milk. It is the fermentation of the milk sugar lactose into lactic acid that gives yogurt its gel-like texture and characteristic tang.
Yogurtmaking involves the introduction of specific "friendly" bacteria into pasteurized milk under very carefully controlled tempurature and environmental conditions. The bacteria ingest the natural milk sugars and release lactic acid as a waste product; the increased acidity, in turn, causes the milk proteins to tangle into a solid mass, or curdle. Generally a culture includes two or more different bacteria for more complete fermentation; the most commonly used microbes are Streptococcus salivarius and Lactobacillus bulgaricus, although sometimes another member of the Lactobacillus genus is used, such as L. acidophilus. If the yogurt is not heated to kill the bacteria after fermentation it is sold as containing "live active culture", which some believe to be nutritionally superior.
Because live yogurt culture contains enzymes that break down lactose, some individuals who are otherwise lactose intolerant find that they can enjoy yogurt without ill effects. Nutritionally, yogurt is rich in protein as well as several B-vitamins and essential minerals, and it is as low in fat as the milk it is made from.
History
Yogurt is traditionally believed to be an invention of the Bulgar people of central Asia, although there is evidence of cultured milk products in other cultures as far back as 2000 BC. The earliest yogurts were probably spontaneously fermented, perhaps by wild bacteria residing inside goatskin bags used for transportation.
Yogurt remained primarily a food of central and eastern Europe until the 1900s, when a Russian biologist named Elie Metchnikoff theorized that heavy consumption of yogurt was responsible for the unusually long lifespans of the Bulgar people. Believing lactobacillus to be essential for good health, Metchnikoff worked to popularize yogurt as a foodstuff throughout Europe. It fell to a Spanish entrepeneur named Isaac Carasso to industrialize the production of yogurt, however; in 1919 he started a commercial yogurt plant in Barcelona, naming the business Dannon after his son.
Homemade yogurt
Yogurt can be made at home by the curious or daring, using a small amount of store-bought plain yogurt as the starter culture. One very simple recipe starts with a quart (litre) of lowfat milk, but requires some means to incubate the fermenting yogurt at a constant 46 °C for several hours.
- Bring the milk to (185 °F) 85 °C over a stove and keep it there for two minutes, to kill any undesirable microbes.
- Pour the re-pasteurized milk into a tall, sterile container and allow to cool to 115 °F (46 °C)
- Mix in 1/2 cup (120ml) of plain active-culture yogurt and cover tightly.
- After about six hours of incubation at precisely 115 °F (46 °C), the entire mixture will have become a very plain but edible yogurt with a somewhat custard-like consistency.