Kumis (/ˈkuːmɪs/ KOO-mis, rarely /ˈkʌmɪs/ KUM-is), alternatively spelled coumis or kumyz,[a] also known as airag (/ˈaɪræɡ/ EYE-rag),[b] is a traditional fermented dairy product made from mare milk.

[9] Rinchingiin Indra, writing about Mongolian dairying, says "it takes considerable skill to milk a mare" and describes the technique: the milker kneels on one knee, with a pail propped on the other, steadied by a string tied to an arm.

A foal starts the milk flow and is pulled away by another person, but left touching the mare's side during the entire process.

Traditionally, this fermentation took place in horse-hide containers, which might be left on the top of a yurt and turned over on occasion, or strapped to a saddle and joggled around over the course of a day's riding.

[12] In modern, controlled production, the initial fermentation takes two to five hours, at a temperature of around 27 °C (81 °F); this may be followed by a cooler aging period.

[13] Kumis itself has a very low level of alcohol, between 0.7 and 2.5%,[14] comparable to small beer, the common drink of medieval Europe that also helps to avoid the consumption of potentially contaminated water.

[17] No specific evidence for its fermentation has yet been found, but considering the location of the Botai culture and the nutritional properties of mare's milk, the possibility is high.

[19] Apart from the idiosyncratic method of mare-milking,[20] it matches up well enough with later accounts, such as this one given by 13th-century traveller William of Rubruck: This cosmos, which is mare's milk, is made in this wise.

[21]Rubruk also mentions that the Mongols prized a variety of kumis he calls caracomos ("black comos"), which was reserved for "great lords".

The serving of it is an essential part of Kyrgyz hospitality on the jayloo or high pasture, where they keep their herds of animals (horse, cattle, and sheep) during the summer phase of transhumance.

[24][25][26][27] The famous Russian writer Leo Tolstoy in A Confession spoke of running away from his troubled life by drinking kumis.

[28] The Russian composer Alexander Scriabin was recommended a kumis diet and "water cure" by his doctor in his twenties, for his nervous condition and right-hand injury.