Fermented milk results from the fermentation of lactose, which involves acidification of the end product.
The consumption of fermented milk is very old, in the Mediterranean basin in particular where a large variety of such milks exists (called leben in Egypt, mast in Iran, iben in North Africa, etc...).
Fermented milk of mare (koumisz), or of cow (kefir) is being consumed in the Caucasus and in Central Asia.
Yoghourt is the form in which fermented milk is mainly consumed. Its consumption has been considerably increased in association with the industrialization of its production, and its distribution by supermarkets.