Why it works: Potato and onion are a kitchen classic. They rank in the top 3% of all ingredient pairs, and cooks put them together in 9,023 recipes. Both carry 2-isopropyl-3-methoxypyrazine, which smells earthy, pea. The science ↓
Lentil Soup
Ingredients
Directions
Prepare the base
Chop the onion roughly and fry it in the butter until it begins to brown.
Pick and wash the lentils, then set them over the fire with 8 cups of water or vegetable stock, adding the fried onion.
Peel, wash, and cut the potatoes, prepare the celery, and cut it into small pieces, then add all to the lentils.
Cook and finish
When the lentils are nearly soft, add the tomatoes.
Once all ingredients are tender, strain them through a sieve.
Return the soup to the saucepan, add pepper and salt, and more water if the soup is too thick.
Serve with slices of toast.
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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Potato + oniontop 3% of all pairsSmell alikemoderateCooked together9,023 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Celery + tomatotop 4% of all pairsSmell alikemoderateCooked together3,377 recipes
Shared aroma: 4'-methylacetophenone (bitter almond).
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Celery + peppertop 5% of all pairsSmell alikestrongCooked together16,012 recipes
Shared aroma: 4'-methylacetophenone (bitter almond).
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Potato + tomatotop 5% of all pairsSmell alikestrongCooked together2,798 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Lentils + celerytop 6% of all pairsSmell alikestrongCooked together316 recipes
Shared aroma: coumarin (sweet, hay).
Ranks compare each pair with 20,000 random ingredient pairs on CompKitchen. How we score pairs
What each ingredient does
- Lentils
- Form the body of the soup and thicken it as they break down during cooking.
- Potatoes
- Add starch that gives the soup a creamier, thicker texture as they cook.
- Tomatoes
- Add acidity and savoury flavour that balances the earthy lentils.
- Butter
- Carries the flavour of the onion and adds richness when frying.
- Onion
- Browning in butter builds sweet, savoury depth as the base of the soup.
The step that matters
Straining the soup through a sieve. Straining after the vegetables are fully tender removes fibrous celery and skins, giving a smooth texture. Adding the tomatoes only when the lentils are nearly soft prevents them from breaking the lentils down too early and dulling the flavour.
Swap the lentils
How well each one fits the dish's main ingredients (potato, onion, celery, tomato, butter, pepper):
- Beansfits better
- Chickpeafits better
- Black-eyed peafits about as well
- Lentilsthe original
Fit is the average pairing score against potato, onion, celery, tomato, butter, pepper. 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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