What is a Roux? The Foundation of 5 Mother Sauces
A roux is two ingredients and one pan. But it's also the technical foundation of classic French cooking — and the difference between a sauce that coats and one that runs.
Definition
A roux is a cooked paste made from equal weights of fat and flour. In practice, this usually means butter and all-purpose flour, stirred together in a pan over medium heat until the raw flour taste cooks out. The roux is then used as a thickening agent — liquid (milk, stock, or both) is added and whisked in, and the starch in the flour absorbs the liquid and thickens it into a sauce.
When to Use It
Use a roux when you need to thicken a sauce with a smooth, velvety consistency rather than the slippery, starchy quality you get from cornstarch. Béchamel (milk + white roux) is the base for macaroni and cheese, lasagna, croque madame sauce, and cream soups. Velouté (stock + blonde roux) is the base for light cream sauces and gravies. In Cajun cooking, a dark or brick roux is the foundation of gumbo and étouffée.
How to Make a Roux
- Melt butter in a heavy-bottomed pan over medium heat.
- Add an equal weight of flour all at once and stir immediately with a wooden spoon or whisk.
- Cook, stirring constantly, for the length of time appropriate to the roux type you're making (see types below).
- Add your liquid (warm stock or milk) gradually at first, whisking constantly to prevent lumps.
- Once all liquid is incorporated and no lumps remain, continue cooking over medium heat, stirring, until the sauce thickens to your desired consistency.
Roux types: White (2–3 min) → Blonde (5–7 min) → Brown (10–15 min) → Dark/Brick (30–45 min)
Common Mistakes
- Adding liquid too fast. Adding too much liquid at once creates lumps before the starch has a chance to disperse. Add liquid gradually and whisk constantly.
- Wrong liquid temperature. Cold milk added to a roux too quickly creates lumps. Warm your liquid first or add it very slowly.
- Not cooking the flour long enough. A roux that hasn't cooked at least 2–3 minutes will give your sauce a raw, pasty flour flavor.
- Burning the roux. Dark roux requires patience and attention — stir constantly and reduce heat if the color progresses too fast.
If your sauce turns out lumpy, see Fixing a Watery or Broken Sauce — a lumpy roux can sometimes be rescued by whisking and gentle heat.
Recipes That Use a Roux
- Creamy Mushroom Orzo — béchamel-style sauce thickened with a brief roux
- Rotisserie Chicken and White Bean Soup — light velouté-style thickening
- 30-Minute Lentil Soup — optional roux for creamier consistency
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Frequently Asked Questions
- What is a roux in cooking?
- A cooked paste of equal parts fat and flour, used to thicken sauces. The foundation of béchamel, velouté, and espagnole — three French mother sauces.
- What are the types of roux?
- White (2–3 min, pale) → Blonde (5–7 min, golden) → Brown (10–15 min, nutty) → Dark/Brick (30–45 min, used in gumbo). Each is darker, more flavorful, and a slightly less effective thickener than the last.
- Does a roux have to use butter?
- No — any fat works. Duck fat, lard, vegetable oil, or drippings all produce a roux. The fat's flavor carries through into the sauce.
- Why does my sauce made with roux turn out lumpy?
- Adding liquid too fast or at the wrong temperature. Add liquid gradually while whisking constantly. Warm the liquid before adding to hot roux.
Further reading: What is Reducing a Sauce? — roux-based sauces are often finished with reduction for additional concentration.