Traditions
Kefir, Kumis, Kashk and Skyr: How the World Ferments Milk
The families of fermented dairy, the organisms behind each, and why some are drinks, some are solid, and some keep for years without refrigeration.
8 min read ·
What is kumis, and why is it slightly alcoholic?
Kumis — also written kymyz, qymyz or koumiss — is fermented mare's milk, the traditional drink of the Kazakh, Kyrgyz, Mongolian and Bashkir steppe. It is thin, sharply sour, faintly effervescent and mildly alcoholic, and it is made by souring raw mare's milk in a skin or wooden vessel with vigorous, repeated agitation over hours.
The alcohol comes from the substrate. Mare's milk contains substantially more lactose than cow's milk and far less casein, so it does not set into a curd; instead, lactose-fermenting yeasts convert sugar to ethanol and carbon dioxide while lactic acid bacteria acidify in parallel. The result is a mixed lactic-alcoholic fermentation, typically finishing at a low single-figure alcohol percentage. Cow's milk fermented the same way gives a different product — kefir's near relative — because there is simply less sugar to convert.
What is kashk?
Kashk is a concentrated, salted dairy product of the Iranian plateau, the Caucasus and Central Asia, made by fermenting milk or buttermilk, straining out the whey, salting the solids and drying them. The Turkish keş and the Central Asian qurut belong to the same family. Depending on where it is made and how far it is taken, kashk arrives as a thick pourable cream, a soft paste, or rock-hard white balls that keep for years in a dry room.
The fermentation is the flavour step; the drying is the preservation step. Removing water below the level at which microorganisms can grow is what allows a dairy product to survive a summer without a refrigerator, and it explains why this family appears wherever herding traditions had to store the spring milk surplus for later. Rehydrated in water and stirred into a soup or a dish of aubergine, kashk returns to something close to its original texture — with a sharpness that has been concentrating the whole time.
How does kefir differ from yoghurt?
Yoghurt is a two-organism, thermophilic, purely lactic ferment: Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus grown together at 42–45 °C for four to eight hours until the milk sets. It is not effervescent, contains no meaningful alcohol, and is reproducible enough to be an industrial commodity.
Kefir is a mesophilic, mixed ferment carried by kefir grains — irregular cauliflower-like structures in which dozens of bacterial and yeast species are embedded in a polysaccharide called kefiran. It ferments at room temperature in twelve to twenty-four hours, produces carbon dioxide and a trace of ethanol, and pours rather than sets. The grains are recovered by straining and used again indefinitely, which makes kefir one of the very few dairy ferments where the culture is a physical object you keep rather than a starter you buy.
Why are some fermented milks drinks and others solid?
Straining. A set yoghurt is roughly the composition of the milk that made it; hang that same yoghurt in a cloth and the whey drains away, leaving a product that can be twice as concentrated in protein and fat. Icelandic skyr, Levantine labneh, Turkish süzme yoğurt and Greek-style strained yoghurt are all points along that single axis, differing mainly in how far the draining goes and whether the starting milk was skimmed.
Beyond straining lies drying, and beyond drying lies the pressed, salted, stored products — kashk, qurut, chhurpi — which are no longer recognisable as milk at all. Read the family in that order and the world's fermented dairy stops looking like a list of unrelated names and starts looking like one process taken to different distances.
Which fermented milks keep without refrigeration?
Only the ones where water has been removed or salt added in quantity. Dried kashk and qurut are the clearest cases: hard, salted, dehydrated, and stable for months to years in dry storage. Long-aged cheeses belong to the same logic. Fresh yoghurt, kefir and ayran do not — acidity slows spoilage but does not replace cold storage, and all three continue to ferment and separate at room temperature.
This is the practical reason the drying traditions cluster in pastoral and high-altitude regions. A herding household with a seasonal milk surplus and no cold storage does not need a better yoghurt; it needs a product that survives until the next season.