Kumis
Kumis is a fermented dairy product traditionally made from mares' milk. The drink remains important to the people of the Central Asian steppes, including the Bashkirs, Kazakhs, Kyrgyz, Mongols and Yakuts.
Kumis is a dairy product similar to kefir, but is produced from a liquid starter culture, in contrast to the solid kefir "grains". Because mare's milk contains more sugars than the cow's or goat's milk fermented into kefir, kumis has a higher, though still mild, alcohol content.  Even in the areas of the world where kumis is popular today, mare's milk remains a very limited commodity. Industrial-scale production of kumis therefore generally uses cow's milk, which is richer in fat and protein but lower in lactose than the milk from a horse. Before fermentation, the cow's milk is fortified in one of several ways. Sucrose, a simple sugar, may be added, to allow a comparable fermentation. Another technique adds modified whey in order to better approximate the composition of mare's milk.

# Terminology and etymology
Kumis is also transliterated  kumiss, koumiss, kymys or kymyz.  It comes from the Turkic word kmz. The word kumis is thought to derive from the name of the Turkic Kumyk people.
The drink is also called airag, ayrag or chigee in Mongolian. 

# Production of mare's milk
A 1982 source reported that 230,000 horses were kept in Russia specifically for producing milk to make into kumis.
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. One arm is wrapped behind the mare's rear leg and the other in front. A foal starts the milk flow and is pulled away by another person, but left touching the mare's side during the entire process.
In Mongolia, the milking season for horses traditionally runs between mid-June and early October. During one season, a mare produces approximately 1,000 to 1,200 kilograms of milk, of which about half is left to the foals.

# Nutritional properties of mare's milk
According to one modern source, "unfermented mare's milk is generally not drunk", because it is a strong laxative. Varro's On Agriculture, from the 1st century BC, also mentions this: "as a laxative the best is mare's milk, then donkey's milk, cow's milk, and finally goat's milk..." Yet today mare's milk is sometimes recommended as a substitute for cow's milk for people with milk allergies, and little mention is made of this laxative effect.
In fact, mare's milk is well-tolerated by people of northern European descent and others who are lactose tolerant. They can digest lactose even as adults; most of the world's population cannot, including the majority in the Central Asian steppes where kumis is popular. Mare's milk has almost 40% more lactose than cow's milk (and, validating Varro's observations, goat's milk has even less); drinking six ounces (190 ml) a day would be enough to give a lactose-intolerant person severe intestinal symptoms. During fermentation, the lactose is converted into lactic acid, ethanol, and carbon dioxide, and the milk becomes an accessible source of nutrition.

# Production of kumis
Kumis is made by fermenting mare's milk over the course of hours or days, often while stirring or churning.  During the fermentation, Lactobacilli bacteria acidify the milk, and yeasts turn it into a carbonated and mildly alcoholic drink.
Traditionally, this fermentation took place in a horse-hide container, which might be left on the top of the yurt and turned over on occasion, or strapped to the saddle and joggled around over the course of a day's riding. Today, a wooden vat or plastic  barrel may be used in place of the leather container.
In modern controlled production, the initial fermentation takes two to five hours at a temperature of around 27C (80F); this may be followed by a cooler aging period. The finished product contains between 0.7 and 2.5% alcohol.
Kumis itself has a very low level of alcohol, comparable to small beer, the common drink of medieval Europe that also avoided the consumption of potentially contaminated water.  Kumis can, however, be strengthened through freeze distillation, a technique Central Asian nomads are reported to have employed. It can also be distilled into the spirit known as araka or arkhi. 

# History
Kumis is an ancient beverage. Herodotus, in his 5th century BC Histories, describes the Scythians' processing of mare's milk:
The milk thus obtained is poured into deep wooden casks, about which the blind slaves are placed, and then the milk is stirred round. That which rises to the top is drawn off, and considered the best part; the under portion is of less account.
It is widely believed that this is a description of ancient kumis making, and 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.  When they have got together a great quantity of milk, which is as sweet as cow's as long as it is fresh, they pour it into a big skin or bottle, and they set to churning it with a stick  and when they have beaten it sharply it begins to boil up like new wine and to sour or ferment, and they continue to churn it until they have extracted the butter. Then they taste it, and when it is mildly pungent, they drink it. It is pungent on the tongue like rape wine when drunk, and when a man has finished drinking, it leaves a taste of milk of almonds on the tongue, and it makes the inner man most joyful and also intoxicates weak heads, and greatly provokes urine.

# Health
Toward the end of the 19th century, kumis had a strong enough reputation as a cure-all to support a small industry of "kumis cure" resorts, mostly in southeastern Russia, where patients were "furnished with suitable light and varied amusement" during their treatment, which consisted of drinking large quantities of kumis. W. Gilman Thompson's 1906 Practical Diatetics reports that kumis has been cited as beneficial for a range of chronic diseases, including tuberculosis, bronchitis, catarrh,  and anemia. Gilman also says that a large part of the credit for the successes of the "kumis cure" is due not to the beverage, but to favorable summer climates at the resorts. Among notables to try the kumis cure were writers Leo Tolstoy and Anton Chekhov. Chekhov, long-suffering from tuberculosis, checked into a kumis cure resort in 1901. Drinking four bottles a day for two weeks, he gained 12 pounds but no cure.

# Consumption
Strictly speaking, kumis is in its own category of alcoholic drinks because it is made neither from fruit nor from grain.  Technically, it is closer by definition to wine than to beer because the fermentation occurs directly from sugars, as in wine (usually from fruit), as opposed to from starches (usually from grain) that had been first worted to be converted to sugars, as in beer. But in terms of experience and traditional manner of consumption it is much more comparable to beer. It is even milder in alcoholic content than beer and is usually consumed cold. It is arguably the regions beer equivalent.
Kumis is very light in body compared to most dairy drinks. It has a unique, slightly sour flavor with a  bite from the mild alcoholic content. The exact flavor is greatly variable between different brewers.
As indicated above, kumis is usually served cold or chilled. Traditionally it is sipped out of small, handle-less, bowl-shaped cups or saucers, called pialkas.  The serving of it is an essential part of Kyrgyz hospitality on the jailoo or high pasture, where they keep their herds of animals (horse, cattle, and sheep) during the summer phase of transhumance.
One custom that may be disturbing to the visitor's notions of hygiene is that of pouring the dregs of each cup back into the kumis storage container.  That way, none is wasted, and the hostess assures herself that there will be enough for future visitors.

# Its cultural role
The capital of Kyrgyzstan, Bishkek, is named after the paddle used to churn the fermenting milk, showing the importance of the drink in the national culture.
In 2005, George W. Bush visited Mongolia, becoming the first U.S. president to do so, "and probably the first to drink fermented mare's milk in a felt tent guarded by the latter-day Golden Horde and a herd of camels and yaks", according to the Washington Post. The same article casts doubt on whether Bush actually drank: "No word on whether Bush actually swallowed or not, but some of his aides evidently did, judging by the looks on their faces afterward."