Yoghurt or yogurt, or less commonly yoghourt or yogourt (see spelling below), is a dairy product produced by bacterial fermentation of milk. It can be made from any milk, including soy milk, but modern production is dominated by cow milk. The fermentation of milk sugar (lactose) produces lactic acid, which acts on milk protein to give yoghurt its gel-like texture and characteristic tang. Yoghurt is often sold in a fruit, vanilla, or chocolate flavor, but can be unflavored. In Tatarstan and some countries of Central Asia, it is known as Katyk.

History

There is evidence of cultured milk products being produced as food for at least 4,500 years, since the 3rd millennium BC. The earliest yoghurts were probably spontaneously fermented by wild bacteria living on the goatskin bags carried by the Bulgars (or Hunno-Bulgars), a nomadic people who began migrating into Europe in the 2nd century AD and eventually settled on the Balkans by the end of the 7th century.

Yoghurt remained primarily a food of South Asia, Central Asia, Western Asia, South Eastern Europe and Central 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 Bulgarian peasants. 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 industrialise the production of yoghurt. In 1919, Carasso started a commercial yoghurt plant in Barcelona, naming the business Danone after his son. It is better known in the United States as 'Dannon'.

Yoghurt with added fruit marmalade was invented to better protect yoghurt against decay. It was patented in 1933 by the Radlická Mlékárna dairy in Prague.