Why it works: Pepper and tomato 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
Prepare the tomatoes
Slice the tomatoes and stew them in their own juice until soft.
Rub the mixture through a fine sieve to remove seeds.
If desired, add sliced onions 15 minutes before adding vinegar and spices.
Make the ketchup
Boil the pulp and juice until thick, like apple butter, stirring constantly to prevent burning.
Mix the vinegar with sugar and spices, then add to the thickened mixture.
Boil twice, then remove from heat and let cool.
Bottle the catsup.
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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Pepper + tomatotop 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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Pepper + cinnamontop 9% of all pairsSmell alikestrongCooked together4,890 recipes
Shared aroma: methyl cinnamate (strawberry).
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Cinnamon + sugartop 10% of all pairsSmell alikelowCooked together30,779 recipes
Shared aroma: guaiacol (smoky, sweet).
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Cinnamon + tomatotop 11% of all pairsSmell alikemoderateCooked together1,348 recipes
Shared aroma: beta-phellandrene (minty, terpene).
Cinnamon and sugar barely smell alike, yet cooks put them together in 30,779 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
- Tomatoes
- Provide the main body, pulp and flavor of the ketchup.
- Vinegar
- Adds acidity that gives the ketchup its tang and helps preserve it.
- Sugar
- Adds sweetness that balances the acidity of the vinegar and tomatoes.
- Black pepper
- Adds sharp aromatic heat to the sauce.
The step that matters
Boil the pulp until thick, stirring constantly. Tomato pulp is thick and sugary, so it scorches easily on the bottom of the pan. Constant stirring prevents burning and lets the mixture reduce evenly to a thick, spreadable consistency.
Swap the onion
The recipe marks onion as optional. How well each one fits the dish's main ingredients (vinegar, pepper, cinnamon, sugar, tomato):
- Capsicumfits better
- Mustardfits better
- Cucumberfits better
- Onionthe original
Fit is the average pairing score against vinegar, pepper, cinnamon, sugar, tomato. 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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