Why it works: Mustard and onion match in chemistry and in kitchens. They rank in the top 6% of all ingredient pairs, and cooks put them together in 9,259 recipes. Both carry 2-isopropyl-3-methoxypyrazine, which smells earthy, pea. The science ↓
Tomato Ketchup
Ingredients
Directions
Boil the ripe tomatoes for one hour and strain through a sieve.
To one quart of juice, add cinnamon, black pepper, cayenne, ground mustard, coarse sea salt, and chopped onions.
Boil the mixture for three hours.
To each quart of juice, add one pint of cider vinegar and boil for an additional 30 minutes.
Bottle the ketchup while hot.
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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Mustard + oniontop 6% of all pairsSmell alikestrongCooked together9,259 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Cider + vinegartop 6% of all pairsSmell alikemoderateCooked together3,431 recipes
Shared aroma: 4-ethyl-2-methoxyphenol (smoky, clove).
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Cinnamon + mustardtop 7% of all pairsSmell alikestrongCooked together1,581 recipes
Shared aroma: guaiacol (smoky, sweet).
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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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Mustard + vinegartop 7% of all pairsSmell alikemoderateCooked together14,067 recipes
Shared aroma: isobutyraldehyde (malty, green).
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, moisture and tomato flavour that the ketchup is built on.
- Onions
- Add savoury depth and aroma that rounds out the sweetness and acidity.
- Cider vinegar
- Adds acidity that brightens the flavour and helps preserve the finished ketchup.
- Black pepper
- Contributes sharp, aromatic heat that balances the tomato's sweetness.
The step that matters
Boil the mixture for three hours. Long simmering evaporates water and concentrates the tomato solids, which thickens the ketchup and deepens its flavour. Stopping early leaves it thin and watery.
Swap the cinnamon
How well each one fits the dish's main ingredients (tomato, pepper, mustard, onion, cider, vinegar):
- Garlicfits better
- Thymefits better
- Tarragonfits better
- Cinnamonthe original
Fit is the average pairing score against tomato, pepper, mustard, onion, cider, 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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