Name: Sweet Pepper Catsup
Ingredients: 100 large red sweet peppers; 2 large onions; vinegar

Why it works: Pepper and onion 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 ↓

Sweet Pepper Catsup

Ingredients

100 large red sweet peppers
2 large onions
vinegar

Directions

Prepare

Boil the sweet peppers and onions until soft.
Strain off the water and rub the pepper pulp through a colander.

Finish and bottle

Thin the mixture to the desired consistency with vinegar.
Heat the catsup and bottle it.

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.

Pepper + oniontop 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).
Pepper + vinegartop 14% of all pairs

Smell alikemoderate

Cooked together27,814 recipes

Shared aroma: 4'-methylacetophenone (bitter almond).

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

What each ingredient does

Red sweet peppers: Provide the main body, flavour and pulp that forms the ketchup.
Onions: Add savoury depth and soften to blend into the pulp.
Vinegar: Adds acidity and sets the final consistency by thinning the mixture.