Name: Pickled Onions
Ingredients: small silver skin onions; coarse sea salt; white wine vinegar; white mustard seeds; grated horseradish

Why it works: Mustard and horseradish match in chemistry and in kitchens. They rank in the top 1% of all ingredient pairs, and cooks put them together in 1,832 recipes. Both carry coumarin, which smells sweet, hay. The science ↓

Pickled Onions

Ingredients

Directions

Peel and trim the onions to the same size.
Place the onions in a stone jar and cover them with a strong boiling salt brine. Let them stand overnight.
The next morning, pour off the brine, heat it again, and pour it over the onions.
On the second morning, heat some white wine vinegar with white mustard seeds and grated horseradish.
Drain the brine and pour the boiling vinegar over the onions.
Once cooled, bottle the onions 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.

Mustard + horseradishtop 1% of all pairs

Smell alikestrong

Cooked together1,832 recipes

Shared aroma: coumarin (sweet, hay).
Onion + mustardtop 6% of all pairs

Smell alikestrong

Cooked together9,259 recipes

Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
Onion + horseradishtop 7% of all pairs

Smell alikestrong

Cooked together1,784 recipes

Shared aroma: coumarin (sweet, hay).
Vinegar + mustardtop 7% of all pairs

Smell alikemoderate

Cooked together14,067 recipes

Shared aroma: isobutyraldehyde (malty, green).
White wine + vinegartop 11% of all pairs

Smell alikemoderate

Cooked together1,776 recipes

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

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

Swap the onion

How well each one fits the dish's main ingredients (white wine, vinegar, mustard, horseradish):

Shallotfits better
Radishfits better
Broccolifits better
Onionthe original

Fit is the average pairing score against white wine, vinegar, mustard, horseradish. Candidates are from the same food group and used in at least 100 recipes.