Ingredient

Crème fraîche

Crème fraîche is cream soured by bacterial culture, and its useful property is that it has enough fat to be boiled without splitting — which soured cream and yoghurt do not.

Why it does not split

When dairy is heated, its proteins tighten and can squeeze out the water and fat around them — which is what curdling is. Fat gets in the way of that process, so the more fat a dairy product has, the more heat it tolerates.

Full-fat crème fraîche is around 30–40% fat, comfortably above the threshold where boiling causes a problem. Soured cream is nearer 18–20% and will split if boiled. Yoghurt is lower still and splits readily.

Acid makes splitting more likely too, which is why an acidic sauce is harder on dairy than a neutral one. Crème fraîche is itself acidic and still survives, because the fat is doing the protecting.

The important consequence: half-fat crème fraîche will split. If a recipe relies on boiling it, buy the full-fat one.

The soured dairy family

Crème fraîche

30–40% fat. Thick, mildly tangy, boils safely. The one to cook with.

Soured cream

18–20% fat. Tangier and thinner. Add off the heat.

Yoghurt

0–10% fat. Sharpest. Splits readily; stabilise with a little cornflour or add at the end.

Double cream

48% fat, unsoured. Boils safely and reduces well, with no acidity.

Mascarpone

Around 40%, barely soured. Very rich, and it holds heat well.

Quark and skyr

Very low fat, high protein. Will split if heated.

Where to use it

• Stirred into a hot sauce at the end, where it enriches and adds a gentle acidity without the flatness of plain cream.
• In a pan sauce after searing chicken or pork, with mustard and a little stock.
• Over hot soup, where it will not split as it warms through.
• In a tart or a quiche filling, in place of some of the cream.
• As a substitute for cream in a reduction where you want acidity to cut the richness.
• Cold, on desserts and fruit. Its acidity balances sweetness far better than plain cream.

Practical points

• Buy full-fat if it is going to be heated. Half-fat is for cold uses only.
• Stir it in off the heat where you can — even a robust dairy is happier not boiled hard.
• It thins when stirred into a hot dish. Add it near the end and let it warm through rather than reducing it.
• You can make a rough version by stirring a spoonful of buttermilk or live yoghurt into double cream and leaving it somewhere warm overnight.
• It keeps well — considerably longer than cream — because the acidity inhibits spoilage. Follow the pack date.
• It does not freeze; it separates.

In baking and puddings

The half of its usefulness that gets forgotten, because it is thought of as a savoury finishing cream.

• In a cake batter, in place of soured cream or yoghurt. The fat gives a tender crumb and the acid reacts with bicarbonate of soda.
• Spooned over hot fruit — a crumble, roasted plums, a tarte tatin — where its sourness cuts sugar better than double cream does.
• Whipped, which it does, to soft peaks. Slightly denser and much tangier than whipped cream.
• Folded into a fruit fool, half and half with whipped cream, which stops the whole thing being cloying.
• In a cheesecake, replacing some of the soured cream, for a sharper set.
• In scones and soda bread, where the acid does the lifting.
• As the base of an ice cream, which gives something close to a frozen yoghurt with a much better texture.

Common questions