How do I thicken a sauce?

Thickening is either removing water or adding something that binds it. Reduction does the first. Starches, roux, cream and purées do the second, and each brings a different texture and flavour, which is why the right choice depends on the sauce.

What you'll need

• Cornflour (optional)
• Butter and plain flour (optional)
• Whisk (optional)

Step by step

1. First decide whether reduction will do the job.Simmer uncovered and let water evaporate. Slowest method, but it concentrates flavour rather than diluting it. Best for pan sauces, tomato sauces and stews.
2. For a fast fix, make a cornflour slurry.One tablespoon cornflour to two tablespoons cold water, mixed smooth. Stir into simmering sauce and cook one minute. Never add dry cornflour straight in — it lumps instantly.
3. For gravies and creamy sauces, use a roux or beurre manié.Beurre manié is equal parts soft butter and flour mashed together, whisked in a small lump at a time. It gives a richer result than cornflour.
4. For soups and stews, blend a ladleful and stir it back.This thickens using the ingredients already in the pot, with no starch flavour and no extra calories.
5. For cream sauces, reduce the cream itself.Cream thickens substantially as it reduces. Do not boil it hard or it can split.
6. Simmer for at least a minute after adding any starch.Undercooked cornflour or flour tastes raw and chalky, and the sauce keeps thickening for a minute after it looks right.

Tips

• Cornflour gives a glossy, slightly translucent finish; flour gives an opaque, matte one. Choose by how you want the sauce to look.
• Cornflour thins again if boiled hard for a long time or if the sauce is very acidic. Flour is more stable for long cooking.
• Add thickener gradually. Thin sauce is easy to fix; over-thickened sauce needs more liquid, which dilutes the seasoning.

Common mistakes

• Adding dry cornflour or flour to hot liquid — The outside gelatinises instantly and seals dry powder inside, producing lumps that never disperse.
• Judging thickness at a rolling boil — Sauces look thinner when hot and thicken further as they cool. Check at a simmer and slightly under-thicken.
• Not cooking the starch out — A raw floury taste is obvious and cannot be seasoned away.

Questions people ask