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French Mustard

A mustard condiment made by steeping onion in vinegar, then adding salt, sugar, egg, 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

Prepare the onion

  1. Slice the onion and cover it with vinegar.

  2. After two days, pour off the vinegar.

Make the mustard

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

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

Cool and use

  1. Let it cool; it is ready for use.

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. Sugar + vinegartop 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

Egg
Sets as it heats, thickening the mixture into a smooth, creamy body.
Mustard
Provides the sharp, pungent flavour and helps thicken the liquid.
Vinegar
Adds acidity that gives the mustard its tang and softens the onion.
Onion
Contributes aroma and savoury flavour as it steeps in the vinegar.
Sugar
Adds sweetness that balances the sharpness of the vinegar and mustard.

The step that matters

Stirring the egg mixture over boiling water. The egg proteins set as they heat, which thickens the mustard. Constant stirring keeps the heat even and prevents the egg from scrambling into lumps, so the result stays smooth and thick.

Swap the onion

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

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

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