Why it works: Tomato and pepper are a kitchen classic. They rank in the top 7% of all ingredient pairs, and cooks put them together in 17,923 recipes. Both carry 2-isopropyl-3-methoxypyrazine, which smells earthy, pea. The science ↓
Tomato Catsup
Ingredients
Directions
Make the ketchup
In a large pot, combine the peeled tomatoes, salt, brown sugar, sliced onions, red pepper, and mixed ground spices.
Boil the mixture until the tomatoes and onions are soft.
Strain the mixture through a sieve to remove solids.
For every gallon of liquid, add 1 pint of vinegar.
Boil again until the catsup reaches your desired thickness.
Bottle
Bottle the hot catsup and seal.
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.
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Tomato + peppertop 7% of all pairsSmell alikemoderateCooked together17,923 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Tomato + oniontop 8% of all pairsSmell alikemoderateCooked together20,633 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Onion + peppertop 11% of all pairsSmell alikemoderateCooked together68,474 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Onion + vinegartop 14% of all pairsSmell alikemoderateCooked together18,226 recipes
Shared aroma: acetic acid (sour, vinegar).
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Pepper + vinegartop 14% of all pairsSmell alikemoderateCooked 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
- Peeled tomatoes
- Form the bulk of the ketchup and provide its main body and flavor.
- Sliced onions
- Soften during boiling and add savory depth to the sauce.
- Vinegar
- Adds acidity that gives the ketchup its tang and helps preserve it.
- Brown sugar
- Adds sweetness that balances the acidity of the vinegar and tomatoes.
The step that matters
Boil again until the thickness is right. Boiling evaporates water, so the ketchup thickens gradually. Stopping too early leaves it thin, while overcooking makes it dense and can scorch the bottom of the pot.
Swap the onion
How well each one fits the dish's main ingredients (tomato, sugar, pepper, vinegar):
- Capsicumfits better
- Cucumberfits better
- Mustardfits better
- Onionthe original
Fit is the average pairing score against tomato, sugar, pepper, vinegar. 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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