Roux
A roux is a cooked paste of fat and flour, usually in equal weights, used to thicken sauces, soups, stews and gravies. Cooking the flour in fat coats each starch granule so it disperses smoothly in liquid and removes the raw flour taste. Roux is the base of béchamel, velouté, espagnole and gumbo.
How roux thickens
Flour is about 70–75% starch. When liquid is added and heated, the starch granules absorb water and swell, a process called starch gelatinization, which happens mostly between about 60 and 95 °C / 140 and 203 °F. Swollen granules and leaked starch chains tangle together and thicken the liquid.
The fat's job is to separate granules before they meet water. Without it, flour clumps into lumps with dry centres.
Types of roux
| Roux | Cook time (medium-low) | Colour and flavour | Used for |
|---|---|---|---|
| White | 2–5 min | Pale, neutral | Béchamel, cream soups |
| Blond | 5–10 min | Straw, lightly nutty | Velouté, gravies |
| Brown | 15–30 min | Peanut-butter brown, toasty | Espagnole, dark gravy |
| Dark (Cajun) | 30–60 min | Chocolate, deep roasted | Gumbo, étouffée |
As roux darkens, heat breaks starch into shorter chains (dextrins). That adds a nutty, roasted flavour but reduces thickening power. A dark roux may need roughly twice as much to thicken the same liquid as a white roux.
Thickening guide
Per 250 ml (1 cup) of liquid:
- Thin (soup): 1 tbsp butter + 1 tbsp flour (about 8 g flour)
- Medium (sauce): 2 tbsp + 2 tbsp (about 16 g flour)
- Thick (binding, croquettes): 3 tbsp + 3 tbsp (about 24 g flour)
Bring the sauce to a simmer and cook at least 5–10 minutes; flour-thickened sauces reach full thickness only near the boil.
Chef Fizz says: Hot roux plus cold milk, or cool roux plus hot stock. Hot plus hot equals lumps!
Tips
- Whisk liquid in gradually, about a third at a time, smoothing out each addition.
- Use butter for flavour in light roux; use oil for dark roux, since butter's milk solids burn.
- Make extra roux and refrigerate it for up to 2 weeks or freeze it in cubes.
- If a dark roux develops black specks or smells burnt, start over. There is no rescue.
For no-cook alternatives, see beurre manié and slurry.
Questions
What is the ratio for a roux?
Equal weights of fat and flour, such as 30 g butter and 30 g flour. By volume, that is roughly 2 tbsp butter to 3–4 tbsp flour, but many cooks simply use equal tablespoons.
How much roux do I need per cup of liquid?
For 250 ml (1 cup) liquid, use about 1 tbsp each of butter and flour for a thin sauce, 2 tbsp each for medium and 3 tbsp each for thick.
Why is my roux sauce lumpy?
The liquid was added too fast or both the roux and liquid were very hot. Add liquid gradually while whisking, or let one of them cool first.
Can you make roux with oil?
Yes. Neutral oil, bacon fat, duck fat or ghee all work. Oil is the usual choice for dark Cajun roux because it tolerates long cooking without burning milk solids.
Why does dark roux thicken less?
Long cooking breaks starch molecules into shorter chains through dextrinization, so they can't build as thick a network. Dark roux can need up to about twice as much for the same thickness.