Milk kefir

Milk kefir is a fermented dairy drink made by adding milk kefir grains, small cauliflower-like clusters of bacteria and yeast, to fresh milk and letting it sit at room temperature for roughly a day. The grains ferment lactose in the milk, thickening it slightly and giving it a tangy, faintly effervescent flavor somewhere between yogurt and buttermilk.

Once fermentation is finished, the grains are strained out of the finished kefir and can be reused immediately in a fresh batch of milk, which makes milk kefir one of the more sustainable home cultures since the grains keep multiplying with regular use. Many people drink milk kefir plain, blend it into smoothies, or use it as a starter for other dairy ferments.

A common early mistake is straining kefir with a metal strainer that reacts with the culture, so many guides suggest plastic or fine mesh nylon instead. Another is letting kefir ferment too long in a warm kitchen, which causes it to separate into curds and a thin, yellowish liquid called whey, a sign that fermentation has gone further than intended rather than a failure, though the flavor becomes noticeably more sour.