Kefir

Kefir is a fermented milk drink, tangy and lightly effervescent, made by fermenting milk with kefir grains, a symbiotic culture of bacteria and yeast bound together in a gelatinous matrix. It originates among the peoples of the North Caucasus mountains, where kefir grains were traditionally treated as a family or clan possession, passed down and shared rather than sold. The exact date of kefir's first use is not established in the historical record. Kefir spread to wider Russian and then international use from the early twentieth century onward, and is now produced industrially and valued for its live bacterial cultures.