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Roux

A brown roux is a mixture of butter and flour cooked until it turns brown, used as a thickening agent.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 3 ingredients
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Why it works: Butter and flour are a kitchen classic. They rank in the top 12% of all ingredient pairs, and cooks put them together in 124,287 recipes. Both carry isobutyraldehyde, which smells malty, green. The science ↓

Roux

Oven, in the book's wordsA cool oven

Ingredients

Directions

  1. Melt the butter in an enamelled pan and skim off any sediment.

  2. Gradually add the flour while stirring continuously.

  3. Once boiling and starting to color, stir more quickly.

  4. Remove from heat if boiling too fast.

  5. Add onion slices when boiling (if desired).

  6. Remove from heat.

  7. Stir until bubbling stops.

  8. Pour off the thick liquid and let it cool before storing in small jars.

Recipe from a historical cookbook (Internet Archive).

Transcribed from a scanned cookbook and modernised for today's kitchens. Where the book gave no heat or time, or said "a moderate oven", the temperatures and times here may be modern equivalents rather than the book's own figures.

Explore the science

The flavor team

The pairs that carry this dish. Each one is judged two ways: how much their aromas overlap, and how often cooks already put them together.

  1. Butter + flourtop 12% of all pairs
    Smell alikelow
    Cooked together124,287 recipes

    Shared aroma: isobutyraldehyde (malty, green).

  2. Butter + oniontop 15% of all pairs
    Smell alikemoderate
    Cooked together42,912 recipes

    Shared aroma: decanal (soap, orange peel).

  3. Flour + oniontop 17% of all pairs
    Smell alikemoderate
    Cooked together32,460 recipes

    Shared aroma: isobutyraldehyde (malty, green).

Butter and flour barely smell alike, yet cooks put them together in 124,287 recipes: they work on texture and structure more than aroma.

Ranks compare each pair with 20,000 random ingredient pairs on CompKitchen. How we score pairs

What each ingredient does

Butter
Provides fat that coats the flour particles and carries the roux's rich flavour.
Fine flour
Starch that thickens the mixture once cooked, and browns as the roux darkens.

The step that matters

Stir quickly once the roux starts to colour. As the flour darkens, it can scorch quickly and turn bitter. Constant stirring and removing the pan from heat when boiling too fast keeps the colour even and the flavour clean.

Swap the onion

The recipe marks onion as optional. How well each one fits the dish's main ingredients (butter, flour):

  1. Shallotfits better
  2. Leekfits better
  3. Arrowrootfits better
  4. Onionthe original

Fit is the average pairing score against butter, flour. Candidates are from the same food group and used in at least 100 recipes.

“What each ingredient does” and “The step that matters” were written by Claude from this recipe’s own method and reviewed in samples by CompKitchen.

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