Equal parts butter and flour. That is all it is. Yet three quarters of the classical sauce kitchen starts with it, from the béchamel in a lasagne to the brown sauce with a stew. Whoever masters roux has half the sauce kitchen in hand.
A roux is a thickening base of fat and flour that you cook briefly together and then turn into a sauce with liquid (milk, stock or fond). Depending on how long you cook the roux, you get a white, a blond or a brown roux, each with its own flavour, colour and thickening power.
What is a roux?
The flour contains starch. When you let the starch swell in hot liquid, the liquid thickens. The fat in the roux coats the starch granules, so they distribute evenly and don’t clump together. That is why you always make a roux with a fat, usually butter, and add the liquid gradually afterwards.
In classical cuisine the basic ratio is equal parts by weight of butter and flour. So 50 grams of butter to 50 grams of flour.
Three kinds of roux
| Kind | Cooking time | Colour and flavour | Use |
|---|---|---|---|
| White roux | about 1 to 2 minutes | pale, neutral, raw flour just gone | béchamel, cheese sauce, croquettes |
| Blond roux | about 4 to 6 minutes | golden, slight nutty flavour | velouté, creamy soups |
| Brown roux | 10 to 20 minutes or longer | brown, nutty, deep flavour | espagnole, brown sauces, stews |
The longer you cook the roux, the darker and more flavourful it becomes, but the less it thickens. The starch partly breaks down during cooking. A brown roux therefore needs more flour than a white one to reach the same thickness.
The darker the roux, the more flavour and the less thickening power.
How to make a roux
Step 1 – Melt the butter
Use a pan with a thick base over medium to low heat. Melt the butter without letting it brown. For a brown roux you can use clarified butter or a neutral oil, because they burn less easily than ordinary butter.
Step 2 – Add the flour
Sprinkle the flour into the butter in one go and stir straight away with a whisk or wooden spoon until a smooth paste forms. It bubbles lightly and smells like warm biscuits.
Step 3 – Cook the roux
Keep stirring, and cook the roux for as long as the kind you want to make. A white roux stays pale, a blond one gets a golden colour, and a brown one turns nut brown. Keep the heat moderate: a roux that browns too fast can taste bitter.
Step 4 – Add the liquid gradually
This is the most important step. The rule is: cold roux with warm liquid, or warm roux with cold liquid, but not both hot. Pour a splash of liquid into the roux and whisk vigorously until a smooth paste forms. Then keep adding more while you keep whisking.
Step 5 – Let the sauce cook through
Bring the sauce to the boil while whisking and then let it simmer gently for 10 to 15 minutes. That removes the taste of raw flour and the sauce reaches its full thickness. Stir regularly, because the sauce can burn on the bottom.
Step 6 – Season and strain
Season the sauce with salt, pepper and for example nutmeg. Strain it if you like for a very smooth texture.
How much roux do you need?
The amount of roux determines the thickness of the sauce. Use this guideline per litre of liquid:
| Desired thickness | Butter | Flour | Use |
|---|---|---|---|
| Thin | 30 g | 30 g | soup, light sauce |
| Medium | 50 g | 50 g | sauce with meat and fish |
| Thick | 80 to 100 g | 80 to 100 g | croquettes, ragout, soufflé |
These are guide weights. A sauce thickens a little more as it cools.
The three sauces that begin with roux
Béchamel
White roux with milk, seasoned with nutmeg. The base for lasagne, gratins, cheese sauce and croquettes.
Velouté
Blond roux with a light stock of chicken, veal or fish. Velvety and neutral, the base of many creamy sauces and soups.
Espagnole
Brown roux with a brown stock, tomato purée and vegetables. A deep, dark sauce, the base of many stews and classical brown sauces.
Together with hollandaise and tomato sauce they form the five mother sauces. Countless other sauces are derived from each of them. You can read more about different ways to thicken under thickeners and liaisons.
Storing roux
You can make roux in advance. Let it cool, keep it covered in the fridge for about two weeks, or freeze it in cubes or in an ice cube tray. That way you always have a quick thickening base. Warm the roux lightly before adding the liquid.
Preventing and fixing lumps
Lumps form when flour in hot liquid forms a layered crust straight away. Prevent them by:
- adding the liquid gradually;
- whisking vigorously with a whisk;
- not using both, roux and liquid, hot;
- stirring the roux smooth first before the liquid goes in.
Are there lumps after all? Whisk the sauce vigorously, strain it or use a stick blender. That solves almost everything.
Alternatives for those who avoid gluten or dairy
A roux contains gluten (in the flour) and milk (in the butter). Those who avoid them can make a roux with olive oil or a plant-based margarine, and replace flour with a gluten-free flour mix or rice flour. For a simple thickening cornflour mixed with cold water also works. Note: the flavour and texture differ slightly.
The most common mistakes
The roux isn’t cooked long enough
The sauce tastes of raw flour.
Solution: cook the roux for at least 1 to 2 minutes and let the sauce simmer for 10 to 15 minutes.
The liquid goes in all at once
Lumps form.
Solution: add the liquid gradually and whisk vigorously.
Both are hot
The flour clumps instantly.
Solution: use cold roux with warm liquid, or the other way around.
The roux burns
The sauce tastes bitter.
Solution: keep the heat moderate, stir constantly and start over if it smells black.
You use too much flour
The sauce becomes sticky and pasty.
Solution: stick to the ratio per litre and dilute if necessary.
Practise with a béchamel
- Melt 50 g of butter in a saucepan.
- Stir in 50 g of flour and cook for 2 minutes, without colour.
- Warm 500 ml of milk and add it bit by bit while whisking.
- Bring to the boil and let it simmer gently for 10 minutes.
- Season with salt, pepper and nutmeg.
You now have a medium-thick béchamel. Add grated cheese and you have a cheese sauce, or let it thicken more for croquettes.
Frequently asked questions about roux
Can I make roux with oil?
Yes. Oil works well and gives a more neutral taste. Butter gives more aroma, especially with white and blond roux.
How long should the sauce simmer?
At least 10 minutes, so the taste of raw flour disappears and the sauce reaches its full thickness.
Why is my sauce too thin or too thick?
Too thin: simmer it down further or add a little beurre manié, balls of equal parts soft butter and flour. Too thick: dilute it with some warm milk or stock.
Can I reheat a sauce made with roux?
Yes, over low heat while stirring. Add a little milk or stock if needed, because it thickens as it cools.
Is brown roux harder to digest?
That is a persistent idea, but there is no reason for it. It is mostly fat and flour. Use it in moderation, like all fatty sauces.
Roux at a glance
- Roux is equal parts butter and flour, weight for weight.
- You make a white, blond or brown roux, depending on the cooking time.
- The darker, the more flavour and the less thickening power.
- Cold roux with warm liquid, or warm roux with cold liquid.
- Add liquid gradually and whisk vigorously.
- Let the sauce simmer for 10 to 15 minutes.
- Béchamel, velouté and espagnole begin with roux.
Remember this
A roux seems like a simple mixture, but it is one of the most important building blocks of classical cuisine. It isn’t about reaching a certain colour. It is about control: adding liquid gradually, whisking calmly and giving the sauce time to cook through.