How to Make a Roux (Blond to Dark)

What a roux does

A roux coats every grain of flour in fat, so when liquid goes in, the starch swells evenly instead of clumping into lumps. Cooking it first also gets rid of the raw, pasty taste of flour. That's the whole idea behind baked mac and cheese with a crisp crumb top, country gravy, chowder and a good pot pie filling.

As the roux cooks longer, the flour toasts and turns nutty, then roasty, then almost like coffee. But browning also breaks down the starch, so a dark roux thickens much less than a pale one. That trade is the most important thing to know: pick the color for flavor, then use enough of it to get the body you want.

The ratio

Use equal parts fat and flour by weight. By volume, that works out to about 1 tablespoon of fat to a slightly heaping tablespoon of flour, or 1/2 cup of oil to 2/3 cup of flour. If you only have measuring spoons, equal volumes are close enough for a light roux; it will just be a little looser.

Which fat: Butter tastes best in light roux for cream sauces and gravy, but its milk solids burn before the roux gets past peanut butter. For anything darker, use a neutral oil like vegetable, canola or peanut, or a mix of oil and bacon or sausage fat. Lard and duck fat work well too.

Which flour: All-purpose. Whole-wheat browns faster and thickens less. Gluten-free blends are uneven; sweet rice flour makes a good light roux for sauces.

How to make a roux, step by step

1. Measure everything first, and have your vegetables or liquid ready next to the stove. Once a roux is going, you can't leave it to chop an onion.
2. Heat the fat in a heavy pot or skillet over medium heat. Cast iron or an enameled Dutch oven holds heat evenly and is less likely to scorch.
3. Add the flour all at once and stir with a flat-edged wooden spoon or heatproof spatula until smooth. It should look like wet sand, then loosen into a paste.
4. Turn the heat to medium-low and keep stirring, getting into the corners and across the whole bottom. For a light roux, a whisk works; for a long dark one, a flat spoon reaches the edges better.
5. Cook until it's the color you want (see the chart). It should smell toasty, never sharp or burnt.
6. Add your vegetables or liquid. Chopped onion, celery and pepper stop a dark roux from cooking further and soften in the heat. For a sauce, whisk in liquid a little at a time at first, then the rest, and bring it to a simmer. It reaches full thickness only once it bubbles.

Roux colors, times and uses

Times are for a medium-low flame and about 1/2 cup each of fat and flour. More roux takes longer; higher heat is faster but much easier to burn.

How much liquid a roux thickens

For a white or blond roux, a tablespoon of flour (with its tablespoon of fat) per cup of liquid is the place to start. Darker roux needs more flour for the same body, because the browned starch has lost much of its power.

The oven method for dark roux

If an hour of stirring isn't in the cards, let the oven do most of it. Heat the oven to 350°F. Whisk equal weights of oil and flour together in a heavy ovenproof pot (a Dutch oven is ideal), slide it in uncovered, and stir every 20 to 30 minutes. It reaches peanut butter in about an hour and dark chocolate in 1 1/2 to 2 hours. Finish it on the stove for a minute or two if you want it a shade darker, then add the vegetables.

It's slower than the stove but almost impossible to burn, and it frees your hands for the chopping. A dark roux also keeps: cool it, cover it, and it lasts 3 months in the fridge. Spoon what you need into a simmering soup and whisk until it melts in.

Common mistakes

• Turning the heat up to hurry. A roux that browns fast browns unevenly and burns at the edges. Medium-low is faster than starting over.
• Walking away. Even for a minute. Flour on the bottom of the pot can scorch in the time it takes to answer the door.
• Keeping a scorched roux. If you see black flecks or smell something sharp, it will make the whole pot bitter. Start over; it's only flour and oil.
• Adding cold liquid all at once to a hot roux, or hot liquid all at once to a cold one. Either can clump. Add the first cup gradually while whisking, then pour in the rest.
• Judging thickness before it boils. Starch only thickens fully at a simmer. Give it 3 to 5 minutes of bubbling before you add more.
• Using a dark roux to thicken a gravy. It won't get thick. Make a lighter roux for body and add flavor another way.
• Getting splattered. A dark roux runs hotter than boiling oil. Add the vegetables carefully, away from you, and keep kids and dogs out of range.