Name: Pickled Onions
Ingredients: 3 quarts onions; boiling water; small handful coarse sea salt; vinegar; sugar to taste; 2 small red peppers (optional)

Why it works: Onion and pepper are a kitchen classic. They rank in the top 11% of all ingredient pairs, and cooks put them together in 68,474 recipes. Both carry 2-isopropyl-3-methoxypyrazine, which smells earthy, pea. The science ↓

Pickled Onions

Ingredients

Directions

Prepare the onions

Pour boiling water over the onions.
Add a small handful of coarse sea salt and cook briefly.

Pickle and bottle

In a separate bowl, mix vinegar with sugar to taste.
Pour the vinegar mixture over the onions in bottles.
If desired, add 2 small red peppers to each bottle for heat.

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.

Onion + peppertop 11% of all pairs

Smell alikemoderate

Cooked together68,474 recipes

Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
Onion + vinegartop 14% of all pairs

Smell alikemoderate

Cooked together18,226 recipes

Shared aroma: acetic acid (sour, vinegar).
Vinegar + peppertop 14% of all pairs

Smell alikemoderate

Cooked together27,814 recipes

Shared aroma: 4'-methylacetophenone (bitter almond).
Vinegar + sugartop 15% of all pairs

Smell alikemoderate

Cooked together20,806 recipes

Shared aroma: beta-damascenone (apple, rose).
Sugar + peppertop 32% of all pairs

Smell alikelow

Cooked together19,401 recipes

Shared aroma: 2-nonenal (fatty, green).

Sugar and pepper barely smell alike, yet cooks put them together in 19,401 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

Onions: Make up the bulk of the pickle and supply its mild, sharp onion flavor.
Vinegar: Provides the acidity that gives the pickle its tangy, sharp flavor.
Sugar: Balances the sharpness of the vinegar with sweetness.