Kefir purportedly from either the Turkish "keyif" (joy/pleasure) or "köpür" ((milk) froth, foam), is a fermented milk drink that originated with shepherds of the Caucasus region, who discovered that fresh milk carried in leather pouches would occasionally ferment into an effervescent beverage. It is prepared by inoculating cow, goat, or sheep's milk with kefir grains. Traditional kefir was made in skin bags that were hung near a doorway; the bag would be knocked by anyone passing through the doorway to help keep the milk and kefir grains well mixed. Dairy-free alternatives are available, such as coconut milk kefir and soy milk kefir.