Science Fair Project Encyclopedia
Yoghurt or yogurt, less commonly yoghourt or yogourt (French-Canadian), 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 milk sugar (lactose) into lactic acid that gives yoghurt its gel-like texture and characteristic tang.
The word derives from the Turkish "yoğurt," deriving from the verb yoğurtmak, which means "to blend," a reference to how yoghurt is made. In Turkish, the word's ğ, indicates its pronunciation [yaw-ghurt], where the gh is similar to the ch used in loch, but voiced. English pronunciation varies in different regions according to the local accent but common pronunciations include , /joʊgɚt/, and /jɔγɚt/ (using IPA).
Yoghurt is traditionally believed to be an invention of the Bulgars people of central Asia, although there is evidence of cultured milk products in other cultures as far back as 2000 BCE. 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 theorised 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 popularise yoghurt as a foodstuff throughout Europe. It fell to a Spanish entrepreneur named Isaac Carasso to industrialise 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 U.S.)
Yoghurt was first commercially produced and sold in the United States in 1929 by Armenian immigrants, Rose and Sarkis Colombosian, whose family business later became Colombo Yogurt.
Yoghurt making involves the introduction of specific "friendly" bacteria into preferably unpasturised, unhomogenised milk (to maintain the healthy balance of bacteria and enzymes of milk in its unprocessed state) 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, (curd). Generally a culture includes two or more different bacteria for more complete fermentation, most commonly Streptococcussalivarius and thermophilus , Lactobacillus bulgaricus, and Lactobacillus genus members, 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. In Spain, the yoghurt producers were divided among those who wanted to reserve the name yogur for live yoghurt and those who wanted to include pasteurised yoghurt under that label (mostly the Pascual Hermanos group). Pasteurised yoghurt has a shelf life of months and does not require refrigeration. Both sides submitted scientific studies claiming differences or their lack between both varieties. Eventually the Spanish government allowed the label yogur pasteurizado instead of the former postre lácteo ("dairy dessert").
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 or high in fat as the milk it is made from.
Yoghurt is often sold sweetened and flavored, or with added fruit on the bottom (often referred to as fruit bottom, to offset its natural sourness. If the fruit is already stirred into the yoghurt it is sometimes referred to as Swiss-style.
Greek "full" yoghurt is made from milk that has been blended with cream to a fat content of exactly ten percent. Standard (5%), low-fat (2%) and non-fat (0%) versions are also made. It is often served with honey or fruit preserves as a dessert. Greek homemade yoghurt is often strained, i.e. put in cheesecloth and left to hang for a few hours to reduce water content. The resulting yoghurt is creamier, richer and milder in taste because of increased fat content. Commercial versions of strained yoghurt are also made.
Lassi is a refreshing yoghurt-based beverage, originally from India where two basic varieties are known: salty and sweet. Salty lassi is usually flavored with ground-roasted cumin and chili peppers; the sweet variety with rosewater and/or lemon, mango, or other fruit juice. A lassi-like, salty drink called Ayran is also quite popular in Turkey. It is made by mixing yoghurt with water and adding salt. The same drink is known as Tan in Armenia. Commercial products resembling sweet lassi began appearing on the U.S. market during 2002, with names like "Drinkable Yogurt" and "Yogurt Smoothie". Many also enjoy yogurt topped with fresh or frozen fruit, often complimenting the fruit taste of the yogurt.
Home made yoghurt is consumed by many people throughout the world, and is the norm in countries where yoghurt has an important place in traditional cuisine, such as Turkey, Bulgaria, and India. Yoghurt can be made at home 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 109.4°F (43°C) for several hours. Yoghurt-making machines are available for this purpose. As with all fermentation processes, cleanliness is very important.
- 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-pasteurised milk into a tall, sterile container and allow to cool to 110°F(43°C)
- Mix in ½ cup (120mL) of the warmed yoghurt 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 yoghurt 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. An electric oven with the light on may work nicely, depending on the bulb size. The further below 110°F (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.
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