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Fermentation Atlas

Fermented milk from Rift Valley and western Kenya

Mursikmursik

Boiled and cooled cow's milk is poured into a gourd (sotet) whose inside has been coated with fresh charcoal from chosen trees, then left closed for three to five days or longer and stirred or shaken. Lactic bacteria and yeasts sour it, and the charcoal turns it bluish-grey and smoky. Mursik is the hospitality drink of the Kalenjin and is served to returning athletes. Made in 5 steps over 3.1 months. The longest step, shake and serve, or keep in the gourd, takes up to 3 months (Mureithi W 2000). Lactobacilli and Yeasts in every starter studied (Candida krusei, C. kefyr, Cyberlindnera sphaerica, Saccharomyces fermentati); 7–90 % of the microbes do most of the fermenting.

Key numbers
Main stepup to 3 monthsReported[mureithi2000]Shake and serve, or keep in the gourd
AciditypH 3.5Measured[hawaz2025]Ferment in the closed gourd
Fully documentedFermented milk3.1 monthsMore fermented milkMore from Kenya

Recipe

No fixed amounts recordedHousehold method with no fixed amounts; a gourd is filled with the day's surplus milk.
Cow's milk, boiled and cooled · Milk is usually boiled before natural fermentation all over Kenya[fao-tmp][hawaz2025]
Charcoal from a chosen tree · Senna didymobotrya is the first choice in Trans-Nzoia; the Tugen use Euclea divinorum[mureithi2000]
No added starter · The gourd and the household's milk carry the microbes[hawaz2025]
Starter: spontaneous (backslopping through the gourd)

Total time across the recorded steps: 3.1 months

Start
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What changes: The milk gourd is cleaned out and left to dry

Step 1 of 5
Clean and dry the gourd
Time
Not documented
Temperature
Not documented
Salt
None given
Acidity
Not documented
Which microbes the steps name, step by step
Lactobacilli sour
Yeasts
L. entilactobacillus
L. casei
Levilactobacillus brevis

Output: clean, dry gourd.

Flavour
Not documented
Texture
Not documented
Colour
Not documented

Microbes at work in this step

Not documented for this step.

Method

Measured measured in a studySet fixed by a specification or tested recipeReported one source reports itTypical a general value, not sourced for this fermentUnconfirmed not yet checked against a source

What makes this one different

Mursik is boiled before souring and fermented in a gourd lined with crushed charcoal, which gives its grey colour and smoky taste. It is also stirred while it ferments, which most other Kenyan sour milks are not, and Maasai kule naoto is made from unboiled milk.

Related ferments

Variants

  • MariwaAnother Kenyan milk coloured with charcoal of the senetwet tree (FAO).
  • Tugen murskik (Baringo)Charcoal from Euclea divinorum.

Safety

Seven of eight family starter cultures studied made acetaldehyde above the 100 µmol/L level counted as mutagenic, and four made more than 1,000 µmol/L; the four strongest also had about 79.4 mmol/L ethanol (Nieminen et al. 2013). A Nandi County case-control study linked frequent mursik drinking with about nine times the odds of oesophageal cancer (Mutai and Mweu 2025), and the charcoal may add polycyclic aromatic hydrocarbons. Gourd hygiene and boiled milk remain the basics.

History and sources

Every number is labelled with how it is known. How this atlas is made

Treating milk with tree charcoal is an old practice of Kenya's pastoral peoples, who used it to keep milk through the dry season, to improve its taste and smell and for its colour; farmers in Trans-Nzoia still rank and plant the trees for it (Mureithi et al. 2000). Mursik is the Kalenjin word for fermented milk.

  1. [hawaz2025] Hawaz H., Bottari B., Scazzina F., Carini E. 2025, Eastern African traditional fermented foods and beverages, advancements, challenges, and perspectives, Compr. Rev. Food Sci. Food Saf. 24(2):e70137 (Table 5 citing Mathara 1999; process citing Nduko et al. 2016)paper
  2. [mureithi2000] Mureithi W., den Biggelaar C., Wesakania E.W., Kamau K., Gatundu C. 2000, Management of trees used in mursik (fermented milk) production in Trans-Nzoia District, Kenya, J. Ethnobiol. 20(1):75–91paper
  3. [nieminen2013] Nieminen M.T., Novak-Frazer L., Collins R. et al. 2013, Alcohol and acetaldehyde in African fermented milk mursik, Cancer Epidemiol. Biomarkers Prev. 22(1):69–75, doi:10.1158/1055-9965.EPI-12-0908 (abstract)paper
  4. [mutai2025] Mutai R.C. and Mweu M.M. 2025, Association between traditional fermented milk (mursik) consumption and oesophageal carcinoma in Nandi County, Kenya, a case-control study, PLoS ONE 20(9):e0324412 (abstract)paper
  5. [fao-tmp] FAO 1990, The technology of traditional milk products in developing countries, II. Acidified milks, 1.1 (mursik, mariwa)gov
  6. [wp] Wikipedia, Mursik (outline only)wiki