Fermented Milks Around the World
Fermentation may be the oldest form of food preservation humans know. Long before refrigeration, before canning, before the germ theory of disease, people discovered that milk transformed by bacterial and yeast activity became something safer, more flavourful, and more shelf-stable than fresh milk. The six fermented milk traditions in the Milkapedia collection span continents, climates, and millennia — and each one creates something that could not exist without the specific community of microorganisms that defines it.
What fermentation does to milk
Fresh milk contains lactose — a sugar. When specific bacteria are introduced to milk and held at the right temperature, they consume the lactose and produce lactic acid. That acidification does several things simultaneously: it lowers the pH, which inhibits the growth of many pathogens; it causes the milk proteins to partially denature, producing a thicker, more gel-like texture; and it creates dozens of flavour compounds that give fermented dairy its characteristic tang.
Some fermented milks also involve yeasts, which convert sugars into carbon dioxide and ethanol. This is why kefir has a slight effervescence and kumis — traditionally made from mare's milk — has a mild alcoholic content (0.7–2.5% ABV). The bacteria-yeast combination produces a different product than bacteria alone: more complex, more variable, and harder to standardise.
The Codex Alimentarius standard CXS 243-2003 sets international definitions for yogurt, kefir, kumis, and fermented milks generally — including required starter cultures and minimum viable microorganism counts at the time of consumption. But traditional preparations often meet different cultural expectations than these standardised commercial definitions, and the Milkapedia entries maintain this distinction throughout.
Quick comparison
| Product | Origin | Milk base | Culture type | Texture | Notable |
|---|---|---|---|---|---|
| Yogurt | Balkans/Middle East | Any dairy | Thermophilic bacteria | Creamy, set or stirred | Oldest mainstream fermented dairy |
| Kefir | Caucasus Mountains | Any dairy | Bacteria + yeasts (grains) | Liquid, mildly effervescent | Up to 50+ microbial species |
| Kumis | Central Asian steppe | Mare's milk | Bacteria + yeasts | Liquid, mildly alcoholic | 0.7–2.5% ABV; 5,500+ year tradition |
| Cultured Buttermilk | South Asia / globally | Cow milk | Mesophilic bacteria | Liquid, tangy | Not the same as traditional churned buttermilk |
| Viili | Finland | Cow milk | Mesophilic bacteria + mould | Ropy, stretchy gel | Geotrichum candidum surface mould |
| Filmjölk | Sweden | Cow milk | Mesophilic bacteria | Pourable, viscous | One of Sweden's most consumed dairy products |
The six fermented milks
🥛 Yogurt
Yogurt is the world's most produced and consumed fermented dairy product. Its legal definition is precise: the Codex Alimentarius standard CXS 243-2003 requires two specific starter cultures — Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus — working in symbiosis. The standard also recognises "alternate culture yoghurt" made with S. thermophilus plus another Lactobacillus species, allowing some variation in the Lactobacillus component. The total starter microorganisms must reach a minimum of 10⁷ CFU per gram at the time of consumption — this is the combined total, not a per-species requirement.
The two cultures work together: S. thermophilus provides the initial acidification; L. bulgaricus breaks down milk proteins and releases amino acids that stimulate S. thermophilus growth. Bulgaria holds a PDO for "Bulgarian yogurt" specifically because the Lactobacillus strain was first documented and isolated there — though the practice of fermenting milk with similar cultures is far older, with evidence of dairy fermentation in Central Asia and the Middle East stretching back 5,000–6,000 years.
🧫 Kefir
Kefir is the most microbially complex fermented milk in the Milkapedia collection. Unlike yogurt — which uses two defined bacterial strains — kefir is produced by "grains": rubbery, cauliflower-like structures containing a symbiotic community of bacteria and yeasts embedded in a polysaccharide matrix (kefiran). Research has identified up to 50 or more different microbial species in artisanal kefir grains, and one amplicon sequencing study found over 200 yeast taxa in traditionally propagated grains. The exact composition varies by grain, region, and how long the culture has been propagated.
The dual bacterial-yeast fermentation produces a mildly effervescent, tangy, slightly alcoholic liquid (0.5–2% ABV in traditional preparations, essentially 0% in commercial versions where yeast activity is suppressed). Kefir's origin is the Caucasus Mountains — the word itself is of Turkic origin. Traditional preparation involved fermenting milk in leather pouches or wooden barrels, adding fresh milk to old grains indefinitely and passing grain cultures between families.
🐴 Kumis
Kumis is among the oldest fermented dairy products with a documented archaeological record — and the oldest with evidence specifically of mare milking at scale: evidence of large-scale mare milking and fermentation has been found at the Botai settlement in northern Kazakhstan, dating to approximately 3500 BCE. The Franciscan friar William of Rubruck described its production and consumption in detail in 1253 at the court of the Mongol ruler Möngke Khan. Leo Tolstoy famously used a kumis cure to treat his tuberculosis in the Samara steppe in the 1860s. Today kumis is still commercially produced and widely consumed in Kazakhstan, Kyrgyzstan, Mongolia, and Bashkortostan, Russia.
What makes kumis distinct from kefir is its milk base: authentic traditional kumis is made from mare's milk, not cow milk. Mare's milk has a different composition from cow milk — notably higher in lactose (5.8–7.0%), lower in fat (1–2%), and with a different protein structure. The higher lactose content provides more substrate for yeast fermentation, which is why traditionally produced kumis has a meaningful alcoholic content. Commercial versions — often made with cow milk — are lighter and less complex.
🥛 Cultured Buttermilk
Cultured buttermilk has a naming problem: it is not what the word "buttermilk" originally meant. Traditional buttermilk was the liquid left behind after churning cream into butter — a byproduct, slightly acidic from the natural fermentation of cream, with residual fat globules and a distinctive flavour. Modern "cultured buttermilk" sold in supermarkets is something else entirely: fresh low-fat milk deliberately fermented with lactic acid bacteria (Lactococcus lactis subsp. lactis and cremoris) to produce a tangy, pourable liquid that approximates the character of traditional buttermilk without requiring butter production.
The distinction matters in cooking: traditional buttermilk and cultured buttermilk can often be used interchangeably in recipes (both are acidic and react with baking soda), but they are different products. The traditional version was historically important across Ireland and India in particular — Irish soda bread relies on its acidity; South Asian chaas and majjiga are drinks made from the buttermilk produced during ghee and butter making.
🇫🇮 Viili
Viili is one of the most unusual fermented milks in the world. Its characteristic texture — a stretchy, ropy gel that can be pulled into long threads — comes from exopolysaccharides produced by its starter culture, primarily Lactococcus lactis subsp. cremoris. But viili is further distinguished by the presence of Geotrichum candidum, a mould that grows on the surface, giving authentic viili a distinctive white, velvety surface layer not found in any mainstream Western fermented dairy product.
Viili is fermented at room temperature — no heating required — and is eaten directly from the container, typically at breakfast with sugar or jam in Finland. It has been made in Finnish homes for generations. Related Nordic cultured-milk traditions include Swedish långfil and Norwegian tettemelk. Milkapedia keeps these room-temperature, mesophilic products separate from strained cultured products whose production methods differ.
🇸🇪 Filmjölk
Filmjölk (literally "film-milk" or "skin-milk" in Swedish) is one of Sweden's most consumed dairy products. Unlike yogurt, which is fermented warm and sets into a firm gel, filmjölk is fermented at room temperature by mesophilic cultures — primarily Lactococcus lactis and Leuconostoc mesenteroides. The Leuconostoc bacteria produce diacetyl during fermentation, giving filmjölk its characteristic buttery, mildly sour aroma that distinguishes it from the sharper, more purely acidic profile of yogurt.
Filmjölk is pourable and slightly viscous — thicker than drinking milk, thinner than yogurt. It is typically eaten with breakfast cereals, muesli, or as a drink. Its relationship to viili and tettemelk places it in the family of Nordic mesophilic fermented milks — all of which share the room-temperature fermentation and gentle sourness compared to the thermophilic yogurt family.
Sources & methodology
Key sources for claims specific to this guide:
- Codex Alimentarius — CXS 243-2003 (Fermented Milks, amended through 2024) — Basis for all Codex definitions, required starter cultures, CFU requirements, and product definitions for yogurt, kefir, and kumis
- PMC — Viili: Finnish Ropy Fermented Milk — Peer-reviewed source for viili starter cultures, Geotrichum candidum mould, and ropy texture mechanism
- PMC — Mare's Milk and Kumis Review — Basis for kumis alcohol content (0.7–2.5% ABV), William of Rubruck 1253 description, and Botai evidence
- Bulgaria PDO claim: EU Protected Geographical Indication register for "Bulgarian yoghurt"
- Tolstoy kumis cure (1860s): documented in multiple historical biographies and literary history sources