The Botai people of modern-day Kazakhstan tamed wild horses on the steppes of Central Asia over five thousand years ago. There, they fermented a beverage, kumis, from the milk of domesticated mares that modern tasters liken to “Champagne mixed with sour cream.” 

For thousands of years, kumis perfectly fit the nomadic, horse-centric life of the steppes. Due to the milk’s naturally high sugar content, making kumis requires nothing but a mare. Mongolian nomads simply churned horse milk in vats, much like butter, until the milk acidified and yeasts produced alcoholic carbonation. People then transported the liquid in leather bags, often hanging them where passersby could easily punch the sack to keep the kumis agitated. For roaming warriors such as Genghis Khan and Attila the Hun, mares provided kumis, meat, and transportation all in one.

The primary reason mare-milkers culture the liquid is to make it drinkable. Unlike cow’s or yak’s milk, mare’s milk contains so much lactose that it has a severe laxative effect. For this reason, unfermented mare’s milk bears certain medicinal qualities, but it’s not considered a nourishing daily staple.

In Central Asia, mothers fed their babies a mild style of nutritious kumis that was low in (but not entirely free of) alcohol, while adults concocted a boozier version for themselves. Around 1250, explorer William of Rubruck journeyed across the steppes and raved about the drink, stating that “Koumiss makes the inner man most joyful!”

Today, companies produce kumis. But it’s rarely fermented long enough to liven up a party—at most, it contains 2 percent alcohol—and it’s usually made with fortified cow’s milk. It’s only steppe-dwellers that make traditional, boozier kumis.