A roux is equal parts fat and flour by weight (roughly equal by volume too), cooked together to thicken sauces, gravies and soups. Melt the fat, stir in the flour, and cook it: a couple of minutes makes a white roux for bechamel and mac and cheese, while 30 to 45 minutes makes a dark roux for gumbo. Here is the counter-intuitive part — the darker the roux, the more flavour it has but the LESS it thickens.
A roux is two things you already have — fat and flour — cooked together. That is all it is. From it come your cheese sauce, your gravy, your gumbo and your cream soups. Get the ratio right, mind the colour, and stir. That is the whole job. Here is how, from scratch.
| Colour | Cook time | Flavour | Thickening power | Best for |
|---|---|---|---|---|
| White | A couple of minutes | Almost none; raw flour just cooked off | Strongest | Bechamel, mac and cheese, cream soups |
| Blond | About 5 minutes | Lightly nutty, biscuity | Strong | Veloute, chicken pot pie, pale gravies |
| Brown | 15 to 20 minutes | Nutty, toasted | Medium | Dark gravies, stews, some gumbo |
| Dark / chocolate | 30 to 45 minutes | Deep, roasted, nutty | Weakest | Cajun and Creole gumbo |
The ratio: equal parts fat and flour by weight
A roux is equal parts fat and flour by weight, and they come out roughly equal by volume too, so a spoon of fat to a spoon of flour will not steer you wrong. Melt your fat over a medium heat — butter, oil, or drippings (the fat and browned juices in the pan) — then stir in the flour. Use plain flour, what American cooks call all-purpose. Cook it, stirring, until it looks and smells right for the job. One rule above all: never tip flour into hot fat and wander off. A roux catches and burns while your back is turned. Stir, and stay with it.
The four colours, set by time on the heat
The only thing that turns a roux from pale to deep is how long you cook it. A couple of minutes gives white; about 5 minutes gives blond; 15 to 20 minutes gives brown; 30 to 45 minutes gives a dark, chocolate-coloured roux for gumbo. As it darkens it grows nuttier and more toasted in flavour. And here is the part that trips people up: the darker it gets, the LESS it thickens. A dark roux has far less thickening power than a white one, which is exactly why gumbo needs so much of it. Pale roux for body, dark roux for flavour.
Roux for mac and cheese (and any cheese sauce)
Mac and cheese starts with a white roux turned into a bechamel. Melt 2 tbsp butter, stir in 2 tbsp plain flour (all-purpose), and cook it just a couple of minutes — you want the raw floury taste gone but no colour at all. Then add 250 ml (1 cup) cold milk gradually, whisking as you go, and it thickens into a smooth white sauce. Take it off the heat before you stir in your grated cheese, so the cheese melts without splitting. Because a white roux is the strongest thickener, a little goes a long way. This is a medium, pourable sauce that clings to the pasta.
Gumbo roux: the dark one
Gumbo wants a dark, chocolate-coloured roux, and that means patience — 30 to 45 minutes of near-constant stirring. Use a neutral oil here rather than butter; over that long a cook, butter's milk solids would burn. Keep the heat medium, keep stirring, and watch it move from blond to peanut butter to milk chocolate. Because a dark roux thickens far less than a pale one, gumbo uses a generous amount of it — you are cooking it for that deep, roasted, nutty flavour more than for thickening. If you see black specks or catch an acrid, burnt smell, it is gone. Tip it out and start again, because burnt roux turns the whole pot bitter.
Gravy from a roux: the '2 and 2'
For a medium gravy, use a '2 and 2': 2 tbsp fat and 2 tbsp flour per 250 ml (1 cup) of liquid. If you have roasted meat, use the drippings as your fat — that is the fat and browned juices left in the pan. Cook the flour in the fat for 1 to 2 minutes first, or the gravy tastes raw, then add your stock or broth gradually, whisking, to keep it smooth. Let it simmer a minute or two to come to full thickness. If you would rather thicken with cornflour (cornstarch), that is a different method — a slurry, not a roux — so keep the two separate.
How to fix a broken or lumpy roux
Lumps come from adding the liquid too fast. Whisk hard and most will smooth out; if a few stubborn ones remain, pass the sauce through a sieve or give it a quick blitz with a stick blender. Next time, add the liquid gradually and whisk between each addition. If the sauce looks oily and split, there is too much fat for the flour — whisk in a little more flour, or a fresh spoonful of roux, to bring it back together. If it has gone claggy and too thick, loosen it with a splash more warm liquid. But if your roux has black flecks or smells scorched, do not try to rescue it. Burnt roux is bitter and will not thicken. Start again.
Questions we get asked
What is the ratio for a roux?
Equal parts fat and flour by weight, which works out roughly equal by volume too — so 1 tbsp fat to 1 tbsp flour. For a medium gravy or sauce, use 2 tbsp fat and 2 tbsp flour per 250 ml (1 cup) of liquid.
Does a darker roux thicken more?
No, it is the opposite. The darker a roux cooks, the more flavour it gains but the LESS it thickens. A dark roux has far less thickening power than a white one, which is why gumbo needs so much more of it.
What fat should I use for a roux?
Butter for cheese sauces and bechamel; drippings (the fat and browned juices in the pan) for meat gravies; and a neutral oil for a long-cooked dark roux, because butter would burn over 30 to 45 minutes on the heat.
How long does it take to make a roux?
It depends on the colour you want. A couple of minutes for white, about 5 minutes for blond, 15 to 20 minutes for brown, and 30 to 45 minutes for a dark gumbo roux. The colour is set entirely by time on the heat.
How do I fix a lumpy roux sauce?
Whisk it hard and most lumps break up. For stubborn ones, pass the sauce through a sieve or blitz it with a stick blender. To avoid lumps in the first place, always add the liquid gradually and whisk as you go.
Can I use cornflour (cornstarch) instead of a roux?
You can thicken with cornflour, but it is a different method — a slurry of cornflour mixed into cold water and stirred into simmering liquid, not a cooked fat-and-flour paste. A roux also adds a flavour that a plain slurry does not.