Thickening

The six methods

Reduction

Boil off water. No additions, concentrates flavour, and it takes time. The best-tasting option and the slowest.

Roux

Flour cooked in fat, then liquid whisked in. Opaque, stable, reheats and freezes well. The base of most classical sauces.

Slurry (cornflour or arrowroot)

Starch slaked in cold liquid and stirred into a simmering sauce. Fast, glossy, semi-clear. Cornflour goes cloudy; arrowroot stays clearer.

Beurre manié

Equal soft butter and flour kneaded together and whisked in at the end. The rescue for a sauce that is nearly finished.

Purée

Blended vegetables, bread, nuts or pulses. Adds flavour and body, and it is what thickens many traditional sauces.

Emulsion

Butter or cream whisked in. Thickens by suspension rather than starch, and it is the least stable.

How each behaves later

This is the part that decides which to use.

• Reduction — reheats and freezes perfectly. Nothing to break.
• Roux — the most robust. Reheats, freezes and holds at temperature. This is why restaurant sauces so often start with one.
• Cornflour — thins on prolonged heating, and can break down if boiled hard or held. It also weeps when frozen and thawed.
• Arrowroot — sets clearer and breaks down faster still with heat. Add it at the very end and do not boil it.
• Beurre manié — behaves like a roux, on a smaller scale.
• Purée — very stable. Freezes and reheats well.
• Butter or cream emulsion — splits on reheating. Make it at the last moment and do not save it.

Avoiding lumps, whichever you use

1. Roux: cook the flour in the fat for a minute or two first, then add the liquid gradually, whisking hard, adding the next splash only once the last is smooth.
2. Slurry: slake the starch in cold liquid until completely smooth before it goes anywhere near heat. Starch added dry to a hot sauce lumps instantly and permanently.
3. Add slurry to a simmering sauce off the boil, stirring as it goes, and give it a minute to thicken before adding more.
4. Beurre manié: knead it completely smooth first, then whisk small pieces into the sauce one at a time.
5. Anything lumpy: whisk hard, then push it through a sieve. A sieve rescues almost every lumpy sauce.
6. Judge it hot. Starch-thickened sauces thicken considerably as they cool, so stop while it looks slightly loose.

Which to choose

For a sauce that will be made and eaten straight away and where clarity matters — a stir-fry sauce, a fruit glaze — use a slurry. It is fast and glossy.

For anything that will be reheated, frozen, or held warm — a lasagne, a pie filling, a gravy made ahead — use a roux. It is the only method that reliably survives all three.

For the best flavour and no additions at all, reduce. For a sauce that is nearly right and slightly thin, beurre manié at the last minute. And for a rustic sauce with flavour as well as body, purée something into it.

Common questions