Name: Pickled Onions
Ingredients: small onions; boiling water; spiced vinegar; horse-radish root; celery; nasturtium seed; red peppers; prepared spices

Why it works: Horse and radish work together. They rank in the top 4% of all ingredient pairs, and cooks put them together in 529 recipes. Both carry 2-methylbutyraldehyde, which smells malty, chocolate. The science ↓

Pickled Onions

Ingredients

Directions

Pour boiling hot salt water over small onions and let them stand until cool, three times: once before peeling and twice after.
Peel the onions.
Cover the peeled onions with hot spiced vinegar.
Add pieces of horse-radish root, celery, nasturtium seed, a few red peppers, and any other prepared spices to the vinegar.

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.

Horse + radishtop 4% of all pairs

Smell alikemoderate

Cooked together529 recipes

Shared aroma: 2-methylbutyraldehyde (malty, chocolate).
Celery + peppertop 5% of all pairs

Smell alikestrong

Cooked together16,012 recipes

Shared aroma: 4'-methylacetophenone (bitter almond).
Onion + celerytop 7% of all pairs

Smell alikemoderate

Cooked together18,518 recipes

Shared aroma: guaiacol (smoky, sweet).
Radish + celerytop 8% of all pairs

Smell alikemoderate

Cooked together101 recipes

Shared aroma: 2-methoxy-4-vinylphenol (clove, smoky).
Vinegar + radishtop 8% of all pairs

Smell alikemoderate

Cooked together508 recipes

Shared aroma: isobutyraldehyde (malty, green).

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 (vinegar, horse, radish, celery, pepper):

Mustardfits better
Cucumberfits better
Cabbagefits better
Onionthe original

Fit is the average pairing score against vinegar, horse, radish, celery, pepper. Candidates are from the same food group and used in at least 100 recipes.