First of all, what is the correct spelling yoghurt or yogurt?
The word is derived from Turkey : yoğurt and is related to yoğurmak 'to knead' and yoğun "dense" or "thick"
In Bulgaria, yogurt is called "кисело мляко" (kiselo mlyako), which means "sour milk"; in Serbia, yogurt is also called "кисело млеко" (kiselo mleko), while Serbian yogurt is a thick, milky liquid produced by fermentation of milk.
In English, there are several variations of the spelling of the word. In Australia and New Zealand "yoghurt" prevails. In the United Kingdom "yoghurt" and "yogurt" are both current, "yogurt" being more common on product labels, and "yoghourt" is an uncommon alternative. In the United States, "yogurt'" is the usual spelling and "yoghurt" a minor variant. In Canada, "yoghurt" is most common among English speakers, but many brands use "yogourt," since it is correct in both official languages.
Whatever the spelling, the word is usually pronounced with a short
o (
/ˈjɒɡət/) in the UK, with a long
o (
/ˈjoʊɡərt/) in North America, Australia and South Africa, and with either a long or short
o in New Zealand and Ireland.
There is evidence of precultured milk products being produced as food for at least 4,500 years.
It is believed that yogurt originated in Mesopotamia thousands of years ago. Evidence has shown that these people had domesticated goats and sheep around 5000
B.C. The milk from these animals was stored in gourds, and in the warm climate it naturally formed a curd.
This curd was an early form of yogurt. Eventually, a process for purposely producing yogurt was developed.
www.answers.com/topic/yoghurt
Fermentation of yogurt is one of the oldest methods practiced by human beings in order to transform milk into products. There is evidence of cultured milk products being produced as food for at least 4,500 years. The exact origin of making fermented milk could be date from some 10000 – 15000 years ago. It might dates back to pre-Biblical times, and Moses reputedly partook of it on his way to promised Land. The earliest yogurts were probably spontaneously fermented by wild bacteria living on the goat skin bags carried by the Bulgars (or Hunno-Bulgars), a nomadic people who began migrating into Europe in the second century AD and eventually settled in the Balkans at the end of the seventh century.
The oldest writings mentioning yogurt are attributed to Pliny the Elder, who remarked that certain nomadic tribes knew how "to thicken the milk into a substance with an agreeable acidity."

Yogurt on Turks
The use of yoghurt by medieval Turks is recorded in the books
Diwan Lughat al-Turk by Mahmud Kashgari and
Kutadgu Bilig by Yusuf Has Hajib written in the 11th century. Both texts mention the word "ortgu" or "yoghurt" in different sections and describe its use by nomadic Turks.
Yogurt on Europeans
The first account of a European encounter with yoghurt occurs in French clinical history: King Francois I suffering from an intestinal complaint (diarrhea) which no French doctor could cure. His ally Suleiman the Magnificent sent a Jewish doctor from Constantinople, who allegedly cured the patient with yoghurt. The doctor arrived on foot with flock of sheep and cured his royal client, but refused to divulge the secret of his concoctions.
A same version with a different ending to the story can be read from Wikipedia which narrates:
That being grateful for curing him, the French king spread around the information about the food which had cured him.
http://en.wikipedia.org/wiki/Yogurti/
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Lactobacillus delbrueckii subsp. bulgaricus |
Until the 1900s, yoghurt was a staple in diets of people in the Russian Empire (and especially Central Asia and the Caucasus), Western Asia, South Eastern Europe/Balkans, Central Europe, and India. Stamen Grigorov (1878–1945), a Bulgarian student of medicine in Geneva, first examined the microflora of the Bulgarian yoghurt. In 1905 he described it as consisting of a spherical and a rod-like lactic acid bacteria. In 1907 the rod-like bacteria was called
Lactobacillus bulgaricus (now
Lactobacillus delbrueckii subsp. bulgaricus).
The Russian Nobel laureate biologist Ilya Ilyich Mechnikov, from the Institut Pasteur in Paris, was influenced by Grigorov's work and hypothesised that regular consumption of yoghurt was responsible for the unusually long lifespans of Bulgarian peasants. Believing
Lactobacillus to be essential for good health, Mechnikov worked to popularise yogurt as a foodstuff throughout Europe.
http://en.wikipedia.org/wiki/Yogurt