It's naturally fizzy and mildly alcoholic — mare's milk ferments so readily that kumys was one of the first alcoholic drinks many steppe peoples ever produced, centuries before wine or beer reached the region.
Kumys is made by fermenting raw mare's milk with a live culture over one to several days, producing a tangy, faintly sour, lightly carbonated drink with a low alcohol content. In Bashkortostan, roadside stands and market vendors sell it chilled from bottles or barrels, especially in summer.