Mursik is the fermented milk of the Kalenjin communities of Kenya’s Rift Valley. Boiled cow’s or goat’s milk is poured into a gourd whose inside has been coated with fine charcoal, and left to ferment for several days. The charcoal gives it a smoky taste and a grey tint. It’s part of daily life – traditionally drunk after every meal (Kigen et al., 2017).
How Mursik Is Made
A review by doctors at Moi University in Eldoret describes the traditional method (Kigen et al., 2017):
- The gourd (sotet): a new gourd is first “sweetened” – bark is placed inside, it’s filled with water and left to cure for three days to remove the bitter taste.
- The charcoal (suteiywo): charcoal from selected trees and shrubs – most often Senna didymobotrya, Juniperus procera, Plectranthus barbatus, wild olive (Olea europaea) and wattle – is ground against the inner wall with a bow-shaped stick (sosiot) until the inside is evenly coated with fine dust.
- The milk: boiled milk is poured in and left to ferment in a cool, dry place – typically 3–5 days (Mutai & Mweu, 2025). The gourd is reused, so microbes carry over from batch to batch.
What Ferments It
When researchers fermented milk with starter cultures from eight Kalenjin families, using the families’ own method, each starter held 2–8 microbial species (5 on average). Yeasts were present in every one, making up anywhere from 7% to 90% of the microbes, alongside lactobacilli (Nieminen et al., 2013). That yeast share is what sets mursik apart from yogurt-type milks, and it matters for the next section.
Other Kenyan fermented milks look different again: in the Maasai fermented milk kule naoto, lactic acid bacteria dominated, mainly Lactobacillus plantarum, and the pH was below 4.5 (Mathara et al., 2004).
Mursik and Oesophageal Cancer: What the Research Says
Oesophageal cancer is unusually common in western Kenya, especially among Kalenjin communities, and researchers have looked at mursik as one possible reason:
- Acetaldehyde: 7 of the 8 family starters above produced acetaldehyde – a carcinogen formed from alcohol – at levels considered mutagenic (over 100 µmol/L), and 4 produced more than 1,000 µmol/L. The same milks contained alcohol. A mix of the yeast Candida krusei and Lactobacillus kefiri went with the highest levels (Nieminen et al., 2013). One author disclosed links to a company working on acetaldehyde reduction.
- A case-control study: at two hospitals in Nandi County, people with oesophageal cancer (33 cases, compared with 131 other patients) were far more likely to drink mursik: about 9 times the odds for frequent drinkers and 3 times for infrequent ones, after adjusting for smoking, alcohol and other factors. The authors suggest charcoal, a possible source of polycyclic aromatic hydrocarbons, may play a role alongside acetaldehyde, and call for safe, community-owned ways of fermenting milk (Mutai & Mweu, 2025).
- Other explanations: a review of the region’s risk factors judged mycotoxins in poorly stored maize, together with traditional alcohol, to be the most likely main cause, with mursik one of several candidates (Kigen et al., 2017).
These are small studies that show an association, not proof that mursik causes cancer. But taken together they are the reason this page doesn’t give a home recipe for charcoal-lined, yeast-rich mursik, or suggest drinking it daily for health.
If You Want a Fermented Milk to Make at Home
Room-temperature fermented milks made with pasteurized milk and a lactic starter are well studied and simple: South Africa’s amasi, Morocco’s raib and Sweden’s filmjölk all have tested recipes on this site. For a drinkable fermented milk with yeasts, kefir is the better-studied choice.