What Is Kefir? Definition, Origin & How It Is Made

Kefir is a fermented milk drink made by culturing milk with kefir grains, a living mix of bacteria and yeast. It is tangy, lightly fizzy, and thinner than yogurt, and water kefir is the dairy-free version made with sugar water.

Kefir is prepared by inoculating milk, most commonly from cows, goats, or sheep, with kefir grains and letting it ferment at room temperature. Over roughly 18–24 hours, the culture breaks down lactose into lactic acid and produces a small amount of carbon dioxide and alcohol, giving kefir its characteristic tang and light fizz.

Unlike yogurt, which uses a small, defined set of bacterial strains, kefir’s culture is a whole community working together, which is part of why it ferments and tastes noticeably different.

Despite the name, kefir grains are not seeds or cereal grains. They are small, rubbery, cauliflower-like clusters made of a symbiotic colony of bacteria and yeasts living together inside a polysaccharide matrix that the culture itself produces.

To learn what they are made of and how they are classified, see what are kefir grains.

Kefir’s origins trace back to the Caucasus Mountains in southern Russia, where local mountain communities are believed to have discovered the fermentation process, likely by accident, when milk stored in animal-skin bags picked up wild bacteria and yeast. The practice spread through Eastern Europe and Russia over centuries before reaching wider global popularity in more recent decades.

Once you understand what kefir is, what are kefir grains covers the culture itself in more depth, and kefir vs. yogurt walks through how it compares to its closest cultured-dairy relative.