Among the fermented beverages which are made from milk kefir has a high rank. It is a beverage prepared from cow's milk by the addition of a special yeast, commonly called kefir grains. Kefir, is nearly related to koumys, and has its origin in the same country. It is made especially in the northern part of the Caucasian mountains. Koumys, is or should be prepared exclusively from mare's milk, and with a different kind of yeast.