Name: Lentil Soup
Ingredients: ½ lb lentils; 3 onions; a little celery top; 2 teaspoons salt; 1 teaspoon pepper; 2 quarts cold water

Why it works: Celery and pepper match in chemistry and in kitchens. They rank in the top 5% of all ingredient pairs, and cooks put them together in 16,012 recipes. Both carry 4'-methylacetophenone, which smells bitter almond. The science ↓

Lentil Soup

Ingredients

Directions

Prepare

Wash the lentils well in several waters.
Wash the celery and cut it small.
Peel the onions.

Cook

Add all ingredients to a saucepan.
Boil slowly for 1½ hours, stirring well.
Strain through a colander, keeping only the pulp.
Reheat the soup in the saucepan and serve.

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.

Celery + peppertop 5% of all pairs

Smell alikestrong

Cooked together16,012 recipes

Shared aroma: 4'-methylacetophenone (bitter almond).
Lentils + celerytop 6% of all pairs

Smell alikestrong

Cooked together316 recipes

Shared aroma: coumarin (sweet, hay).
Onion + celerytop 7% of all pairs

Smell alikemoderate

Cooked together18,518 recipes

Shared aroma: guaiacol (smoky, sweet).
Lentils + oniontop 8% of all pairs

Smell alikestrong

Cooked together1,221 recipes

Shared aroma: coumarin (sweet, hay).
Onion + peppertop 11% of all pairs

Smell alikemoderate

Cooked together68,474 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

Lentils: Break down as they cook, thickening the soup and giving it body.
Onions: Release sweetness and aroma into the broth as they simmer.
Celery: Adds aromatic, savory flavor to the broth.

The step that matters

Boil slowly for 1½ hours. A gentle simmer cooks the lentils evenly and tender without breaking them up too fast. A hard boil can scorch the bottom of the pan as the liquid reduces, so stirring well helps keep the lentils from sticking and burning.