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Dairy ferment

Sour cream / crème fraîche

Beginner

Cream cultured at room temperature until thick and tangy.

Temperature
20–26 °C
Time
12–24 hours
Plus chilling to firm.

Timeline

Sour cream / crème fraîche timeline

  1. Stage 1: Inoculatestart · about 12 min

    Hands-on

  2. Stage 2: Culturefrom 12 min · about 18 h

    Fermenting / waiting — 20–25 °C

  3. Stage 3: Chillfrom 18 h · keeps about 10 days

    Cold storage — Fridge, about 1–2 weeks

Ingredients

  • 250 ml pasteurised cream (single/light for sour cream, double/heavy for crème fraîche)
  • 1 tbsp live cultured buttermilk or a mesophilic culture

Equipment

  • Clean jar with lid

Steps

  1. Stir the culture into the cream.
  2. Cover and leave at 20–25 °C for 12–24 hours until thick.
  3. Chill — it thickens further.

Is it working?

  • Spoonable and thick
  • Clean, tangy, buttery smell

Smell & texture: Clean and tangy; smooth.

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 sour the cream and thicken it; the higher fat makes a richer, more heat-stable result (crème fraîche, with more fat, can be boiled without splitting).

Organisms

  • Mesophilic lactic cultures (Lactococcus, Leuconostoc)

Troubleshooting

Thin
Give it longer or a warmer spot; use higher-fat cream.

A dish (not a ferment) gone wrong? Try Recipe Rescue.

Cook with it

Learn more

Sources

Guidance changes: check the source for current wording. Original text; figures quoted from the sources where stated.