Roux

A roux is flour cooked in fat, usually butter, and used to thicken liquids. It is the base of béchamel, velouté, espagnole, cheese sauce and most gravies. The longer you cook it, the darker, nuttier and thinner-thickening it gets. The word is French for "reddish", from the color of a cooked roux.

How to do it

1. Melt equal weights of fat and flour, for example 30 g (2 tablespoons) butter and 30 g (1/4 cup) flour.
2. Stir in the flour over medium-low heat until smooth.
3. Keep stirring until it reaches the color you need.
4. Whisk in the liquid a little at a time until smooth. A very hot roux and boiling liquid together tend to clump, so use warm liquid.
5. Bring to a simmer and cook for at least 5 minutes so the flour taste cooks out.

How to tell it is done

Roux	Cooking time	Color and smell	Use
White	2 to 3 minutes	Pale, smells like cooked pastry	Béchamel, cheese sauce
Blond	5 to 8 minutes	Light golden, smells like popcorn	Velouté, chicken gravy
Brown	15 to 20 minutes	Peanut butter color, nutty	Espagnole, beef gravy
Dark	30 to 45 minutes	Milk chocolate or darker	Gumbo

Why it works

Fat coats each grain of flour so it spreads through the liquid without clumping. When heated, the starch swells and thickens the sauce. Browning breaks down some of the starch, so a dark roux thickens much less than a white one but adds deep flavor.

Common mistakes

• Burning it. Black specks or a bitter smell mean start over.
• Adding hot liquid to a very hot roux all at once, which makes lumps.
• Not cooking the sauce long enough after adding the liquid, so it tastes floury.
• Using high heat to rush a dark roux.

In recipes

In Cajun and Creole cooking, a dark roux is cooked in oil, then the holy trinity goes in to stop it from cooking further. As a rule of thumb, 1 tablespoon each of butter and flour thickens 250 ml (1 cup) of liquid to a thin sauce.