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French Mustard

A mustard condiment made with onion, vinegar, egg, salt, sugar, and mustard.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 6 ingredients
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Why it works: Onion and mustard match in chemistry and in kitchens. They rank in the top 6% of all ingredient pairs, and cooks put them together in 9,259 recipes. Both carry 2-isopropyl-3-methoxypyrazine, which smells earthy, pea. The science ↓

French Mustard

Ingredients

Directions

Infuse the vinegar

  1. Cover the sliced onion with vinegar and let it sit for two days.

  2. After two days, pour off the vinegar.

Make the mustard

  1. To the vinegar, add salt, sugar, beaten egg, and enough mustard to thicken.

  2. Set the mixture over boiling water and stir until it boils.

  3. Let it cool before using.

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. Onion + mustardtop 6% of all pairs
    Smell alikestrong
    Cooked together9,259 recipes

    Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).

  2. Vinegar + mustardtop 7% of all pairs
    Smell alikemoderate
    Cooked together14,067 recipes

    Shared aroma: isobutyraldehyde (malty, green).

  3. Onion + vinegartop 14% of all pairs
    Smell alikemoderate
    Cooked together18,226 recipes

    Shared aroma: acetic acid (sour, vinegar).

  4. Vinegar + sugartop 15% of all pairs
    Smell alikemoderate
    Cooked together20,806 recipes

    Shared aroma: beta-damascenone (apple, rose).

  5. Sugar + mustardtop 19% of all pairs
    Smell alikemoderate
    Cooked together8,424 recipes

    Shared aroma: guaiacol (smoky, sweet).

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

What each ingredient does

Mustard
Gives the main flavour and, with the egg, helps thicken the sauce.
Egg
Thickens the mixture as it heats, because egg proteins set when cooked.
Vinegar
Provides the sharp acidity and carries the onion flavour into the sauce.
Onion
Flavours the vinegar during the long soak before the vinegar is poured off.
Sugar
Balances the sharpness of the vinegar with a hint of sweetness.

The step that matters

Stirring the mixture over boiling water. Egg proteins set when heated, so the mixture must be stirred constantly and kept over gentle, steady heat. Stirring spreads the heat evenly, helping the egg thicken the mustard smoothly instead of curdling or scrambling in pockets.

Swap the onion

How well each one fits the dish's main ingredients (vinegar, egg, sugar, mustard):

  1. Horseradishfits better
  2. Cucumberfits better
  3. Shallotfits better
  4. Onionthe original

Fit is the average pairing score against vinegar, egg, sugar, mustard. 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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