How do I make a roux?

A roux is flour cooked in fat so the starch can thicken liquid without clumping or tasting raw. It underlies white sauce, gravy, soups and stews, and once you can make one, a whole family of sauces follows.

What you'll need

• Butter or oil
• Plain flour
• Whisk
• Warm liquid (optional)

Step by step

1. Melt equal weights of fat and flour together.Butter is standard, but any fat works — including the fat left after roasting meat, which is how gravy starts.
2. Cook it for at least two minutes, stirring.This cooks out the raw flour taste. Undercooked roux makes a sauce taste chalky, which no seasoning fixes.
3. Choose how far to take the colour.Pale blond for white sauces, golden for velouté, deep brown for gumbo and rich gravies. Darker roux tastes better but thickens less.
4. Add liquid gradually, whisking constantly.A splash at a time at first, whisking smooth before adding more. This is where lumps are prevented.
5. Use warm liquid if you can.It incorporates more easily than cold, though whisking properly matters more than temperature.
6. Simmer for a few minutes after all the liquid is in.It thickens fully and the flour finishes cooking. Sauces thicken more than you expect during this stage.
7. Sieve it if it does lump.Almost every lumpy sauce is recoverable by passing it through a fine sieve. Nobody will know.

Tips

• Roughly 30g each of butter and flour thickens 500ml of liquid to a pouring consistency. Double it for a coating sauce.
• Roux freezes well. A batch in an ice cube tray turns a sauce into a five-minute job.
• For gravy, use the fat in the roasting tin instead of butter — it carries all the flavour of what you roasted.

Common mistakes

• Adding all the liquid at once — The flour cannot disperse and it clumps immediately. Gradual addition with whisking is the entire technique.
• Not cooking the flour before adding liquid — The sauce tastes raw and chalky, and cooking it later does not fix it properly.
• Expecting a dark roux to thicken like a pale one — Browning breaks down the starch. A dark roux tastes better and thickens considerably less.

Questions people ask