Yoghurt (traditional spelling) or yogurt (modern spelling) is a dairy product produced by bacterial fermentation of milk. 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.

Yogurt making 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 Lactobacillus 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.

Yogurt is often sold sweetened and flavored, or with added fruit on the bottom, to offset its natural sourness. If the fruit is already stirred into the yogurt it is referred to as Swiss-style.

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 Ilya Ilyich Mechnikov 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, Mechnikov worked to popularize yogurt as a foodstuff throughout Europe. It fell to a Spanish entrepreneur 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 (or thrifty!), 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 43 °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 110 °F (43 °C)
• Mix in 1/2 cup (120ml) of warmed plain active-culture yogurt and cover tightly.
• After about six hours of incubation at precisely 110 °F (43 °C), the entire mixture will have become a very plain but edible yogurt with a loose consistency.
  • If a precise means of temperature control is not available, put the culture in a warm place such as on top of a water heater or in a gas oven with just the pilot flame burning. The further below 43 °C the temperature, the longer it will take for the yoghurt to solidify; you can tell it is done when it no longer moves if you tilt the jar.

See also: Cheese, Kephir