Name: Lentil Soup
Ingredients: 1 pint Egyptian lentils; 1 quart cold water; 1 small onion, shredded; 1 carrot, shredded; a little parsley; 1 slice fat bacon; milk (to desired consistency); pepper (to taste); coarse sea salt (to taste)

Why it works: Carrot and parsley match in chemistry and in kitchens. They rank in the top 1% of all ingredient pairs, and cooks put them together in 8,053 recipes. Both carry 2,4-decadienal, which smells seaweed. The science ↓

Lentil Soup

Ingredients

Directions

Make the soup

Combine lentils, cold water, onion, carrot, parsley, and bacon in a pot.
Bring to a boil, then reduce heat and simmer for 2 hours, stirring occasionally.
Rub the mixture through a fine sieve using the back of a spoon.

Finish and season

Add milk to achieve a creamy consistency.
Heat the soup again after adding milk, then season with pepper and salt to taste.

Recipe from a historical cookbook (Internet Archive).

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.

Carrot + parsleytop 1% of all pairs

Smell alikestrong

Cooked together8,053 recipes

Shared aroma: 2,4-decadienal (seaweed).
Parsley + peppertop 2% of all pairs

Smell alikestrong

Cooked together34,122 recipes

Shared aroma: 4'-methylacetophenone (bitter almond).
Lentils + parsleytop 5% of all pairs

Smell alikestrong

Cooked together322 recipes

Shared aroma: coumarin (sweet, hay).
Lentils + carrottop 5% of all pairs

Smell alikestrong

Cooked together505 recipes

Shared aroma: coumarin (sweet, hay).
Carrot + peppertop 6% of all pairs

Smell alikestrong

Cooked together14,555 recipes

Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).

Ranks compare each pair with 20,000 random ingredient pairs on CompKitchen. How we score pairs

What each ingredient does

Egyptian lentils: Form the body of the soup and thicken it as they break down during simmering.
Bacon: Adds savory, smoky fat that flavors the broth as it simmers.
Milk: Adds richness and softens the texture, giving a creamy finish.

The step that matters

Rubbing the mixture through a fine sieve. Pushing the cooked lentils and vegetables through a fine sieve breaks them into a smooth purée. Skipping or rushing this leaves the soup grainy, since lentil skins and fibers do not fully dissolve during simmering.

Swap the onion

How well each one fits the dish's main ingredients (lentils, carrot, parsley, milk, pepper):

Parsnipfits better
Turnipfits better
Spinachfits better
Onionthe original

Fit is the average pairing score against lentils, carrot, parsley, milk, 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.