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 ↓
Onions Boiled
Ingredients
Directions
Peel the whole onions.
Boil the onions in water for about 15 minutes.
Turn off the water and add enough hot water to cover the onions.
Boil down the mixture until it reduces to about 4 or 5 tablespoons.
Add salt, pepper, and butter, then serve 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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Onion + peppertop 11% of all pairsSmell alikemoderateCooked together68,474 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Onion + buttertop 15% of all pairsSmell alikemoderateCooked together42,912 recipes
Shared aroma: decanal (soap, orange peel).
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Butter + eggtop 17% of all pairsSmell alikemoderateCooked together118,967 recipes
Shared aroma: decanal (soap, orange peel).
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Pepper + buttertop 21% of all pairsSmell alikemoderateCooked together85,593 recipes
Shared aroma: trans-2-nonenal (cardboard, fatty).
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Pepper + eggtop 33% of all pairsSmell alikelowCooked together50,580 recipes
Shared aroma: 2-nonenal (fatty, green).
Pepper and egg barely smell alike, yet cooks put them together in 50,580 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
- Whole onions
- Main ingredient; boiling softens them and mellows their sharp flavor.
- Butter
- Adds richness and a smooth mouthfeel to the reduced liquid.
The step that matters
Boil down the mixture. As water evaporates, the remaining liquid becomes more concentrated in flavor and salt. Reducing it too far can leave it dry or scorched, so watch it closely until it reaches the target volume.
Swap the onion
How well each one fits the dish's main ingredients (pepper, butter, egg):
- Capsicumfits better
- Asparagusfits better
- Chivefits better
- Onionthe original
Fit is the average pairing score against pepper, butter, egg. 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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