Since ancient time milk has been a staple part of human diet. In antiquity people mostly used milk from sheep and goats. Cow's milk is the preferred choice today. The contemporary technological methods allow for the milk to be stored for up to six months and this makes the product accessible in all parts of the world.
Sour milk and yogurt are a result of the lacto acid fermentation which is caused by a group of bacteria. The main bacteria in this group are Lb. Bulgaricum discovered and described by Bulgarian scientist Dr Stamen Grigorov in 1905. Herodotus was the first author who wrote that the Thracians who used to live on the territory of modern Bulgaria gave us the sheep milk. It is thought that the word yogurt has Thracian origin and it is a compound of the words yogu-hard and rt – milk or if literally translated from ancient Thracian – hard milk.