Fermentation Guide · Beginner

Cultured Sour Cream — Homemade in 24 Hours

How to make cultured sour cream at home — ferment heavy cream with live cultures for thick, tangy sour cream that is better than store-bought. Two ingredients, 24 hours.

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Thick cultured sour cream beside heavy cream and a small buttermilk portion

Updated September 2026 · 6 min read

Cultured sour cream is one of the easiest ferments you can make — heavy cream plus a spoonful of buttermilk, left at room temperature overnight. The lactic acid bacteria in the buttermilk ferment the cream, thickening it and producing the tangy flavour that makes sour cream what it is. No heating, no cooking, no special equipment.

How to make cultured sour cream

250ml Heavy cream
2 tbsp Cultured buttermilk
12–24 hours Fermentation time
~250ml Yield
  1. 1
    Mix Pour 250ml heavy cream into a clean glass jar. Add 2 tablespoons of cultured buttermilk. Stir well.
  2. 2
    Cover loosely Place a lid on the jar without sealing it tightly, or cover with a cloth. The bacteria need a little airflow.
  3. 3
    Leave at room temperature Set the jar on the counter at 20–24°C (68–75°F) for 12–24 hours. At 12 hours, check — the cream should have thickened noticeably and smell tangy. If it is still pourable like cream, give it more time.
  4. 4
    Refrigerate Once it is thick and tangy, seal the jar and refrigerate for at least 4 hours. The cold firms it up further. It will be spoonable and thick — proper sour cream consistency.
A measured yogurt starter portion beside milk and a freeze-dried culture sachet

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Tips for the best results

Use heavy cream, not light light cream and half-and-half do not have enough fat to thicken properly. 35%+ fat is essential.
Check your buttermilk the label must say "live active cultures" or "cultured". Many brands are acidified milk without live bacteria — those will not ferment your cream.
Taste at 12 and 24 hours 12 hours gives a mild tang; 24 hours is more assertive. Go with your preference.
Scale freely the ratio is roughly 1 tablespoon buttermilk per 125ml cream. Double, triple, or halve as needed.

Variations

Crème fraîche Crème fraîche is essentially the same thing — cultured cream. It tends to be slightly thinner and less tangy than sour cream, often because it is fermented for a shorter time (8–12 hours) or at a cooler temperature.
Herbed sour cream After fermentation, stir in finely chopped chives, dill, garlic, or any herbs you like. A squeeze of lemon juice brightens it further.
Mexican-style crema Use a 50/50 mix of heavy cream and whole milk for a thinner, pourable cultured cream similar to Mexican crema. Ferment 12–16 hours.

Watch for

  • Do not use ultra-pasteurised (UHT) cream if you can avoid it — it cultures more slowly and sometimes does not thicken properly.
  • If the cream develops pink, orange, or fuzzy spots, discard it. A thin layer of liquid on top is normal — stir it back in.

FAQ

Frequently asked questions

What is cultured sour cream?
Cultured sour cream is cream that has been fermented with lactic acid bacteria — the same process that makes yogurt and buttermilk. The bacteria produce lactic acid, which thickens the cream and gives it its characteristic tangy flavour. Commercial sour cream often uses thickeners and stabilisers instead of a full fermentation; homemade relies on the bacteria alone.
How do I make sour cream at home?
Stir 2 tablespoons of cultured buttermilk (with live active cultures) into 250ml of heavy cream. Cover loosely and leave at room temperature (20–24°C) for 12–24 hours until thickened and tangy. Refrigerate until set — about 4 hours. That is it.
Can I use yogurt instead of buttermilk as a starter?
Yes. Use 1–2 tablespoons of plain yogurt with live active cultures per 250ml of cream. The flavour will be slightly different — more yogurty than the clean tang of buttermilk-cultured sour cream — but it works well.
Why is my homemade sour cream thin?
It probably has not fermented long enough, or the room is too cold. Give it more time — up to 24 hours. Also make sure you are using heavy cream (35%+ fat), not half-and-half or light cream, which will not thicken properly. Refrigerating for several hours also firms it up significantly.
How long does homemade sour cream last?
2–3 weeks in the fridge in a sealed container. It may continue to thicken and get slightly tangier over time. If it develops mould, off-colours, or smells bad (not just sour), discard it.
Is homemade sour cream better than store-bought?
Most people think so. Commercial sour cream often contains gums, stabilisers, and preservatives, and many brands use a minimal fermentation before adding thickeners. Homemade is pure cream and cultures — the flavour is cleaner, tangier, and richer.
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