Dairy ferment
Cultured buttermilk
Milk thickened and soured by cool-loving (mesophilic) cultures — for baking, marinades and drinking.
- Temperature
- 20–26 °C
- Mesophilic cultures prefer about 22 °C.
- Time
- 12–24 hours
- Set like thin custard when tilted.
Timeline
Stage 1: Inoculatestart · about 12 min
Hands-on
Stage 2: Culture at room temperaturefrom 12 min · about 18 h
Fermenting / waiting — 20–25 °C
Stage 3: Chillfrom 18 h · keeps about 10 days
Cold storage — Fridge, about 10 days
Ingredients
- 1 litre pasteurised milk
- 60 ml shop cultured buttermilk with live cultures, or a mesophilic starter sachet
Equipment
- Clean jar with lid
Steps
- Bring milk to room temperature (or warm to about 22 °C).
- Stir in the buttermilk or culture.
- Cover and leave at 20–25 °C.
- When thick like single cream and pleasantly sour (12–24 hours), refrigerate.
Is it working?
- Thickened, coats a spoon
- Buttery, tangy smell
Smell & texture: Clean, sour and buttery; pourable.
Signs tell you it's fermenting, not that it's safe: never rely on smell or appearance alone.
Safety, mould and discard rules
Mould or yeast?
Dairy ferments should not grow anything on the surface. Any fuzz, spots or coloured patches (pink, orange, green, black) mean contamination: discard the whole batch — don't scrape it off.
Storage
Refrigerate.
Shelf life: About 1–2 weeks in the fridge.
The science: what's happening
Mesophilic lactic bacteria work at room temperature, souring milk and producing diacetyl, the buttery aroma. (Traditional buttermilk and chaas are the liquid left after churning butter, or thinned dahi — different things.)
Organisms
- Lactococcus lactis (incl. diacetylactis)
- Leuconostoc mesenteroides subsp. cremoris
Troubleshooting
- Didn't thicken
- Kitchen too cold or culture inactive — use fresh live buttermilk.
A dish (not a ferment) gone wrong? Try Recipe Rescue.
Cook with it
Learn more
Sources
- Potential Hazards with Fermented Foods — Association of Food and Drug Officials
- Chilling — UK Food Standards Agency
Guidance changes: check the source for current wording. Original text; figures quoted from the sources where stated.