Yoghurt, also spelled Yoghourt or yogurt, is a dairy product produced by bacterial fermentation of milk. Any sort of milk may be used to make yoghurt, but modern production is dominated by cow's milk. It is the fermentation of the milk sugar (lactose) into lactic acid that gives yoghurt its gel-like texture and characteristic tang.
The word derives from the Turkish yogurt, deriving from the verb yogurtmak, which means to blend, referring to how yoghurt is made. In Turkish, the word has a soft g, and is pronouced [yaw-ghurt], where the gh is similar to the ch used in loch but voiced, and thus the European/American pronunciation of the word comes from a misunderstanding of the Turkish soft g.
Yoghurt making involves the introduction of specific "friendly" bacteria into pasteurized milk under very carefully controlled temperature 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 curd. 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 yoghurt is not heated to kill the bacteria after fermentation it is sold as containing "live active culture" (or just as "live" in some countries), which some believe to be nutritionally superior.
Because live yoghurt culture contains enzymes that break down lactose, some individuals who are otherwise lactose intolerant find that they can enjoy yoghurt without ill effects. Nutritionally, yoghurt 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.
Yoghurt 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 yoghurt it is referred to as Swiss-style.
Yoghurt 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 yoghurts were probably spontaneously fermented, perhaps by wild bacteria residing inside goatskin bags used for transportation.
Yoghurt 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 yoghurt was responsible for the unusually long lifespans of the Bulgar people. Believing lactobacillus to be essential for good health, Mechnikov worked to popularize yoghurt as a foodstuff throughout Europe. It fell to a Spanish entrepreneur named Isaac Carasso to industrialize the production of yoghurt. In 1919 he started a commercial yoghurt plant in Barcelona, naming the business Danone after his son (the group trades as Dannon in the US).
Yoghurt can be made at home by the curious or daring (or thrifty!), using a small amount of store-bought plain live active culture yoghurt as the starter culture. One very simple recipe starts with a litre of low-fat milk, but requires some means to incubate the fermenting yoghurt at a constant 43°C for several hours. Yoghurt-making machines are available for this purpose.
History
Homemade yoghurt
See also: Cheese, Kephir