Name: Onion Gruel
Ingredients: 1 very small onion, sliced; ½ pint water; 2 teaspoons flour; 1 small piece of butter; salt to taste

Why it works: Flour and butter are a kitchen classic. They rank in the top 12% of all ingredient pairs, and cooks put them together in 124,287 recipes. Both carry isobutyraldehyde, which smells malty, green. The science ↓

Onion Gruel

Ingredients

Directions

Boil the sliced onion in ½ pint of water for 1 hour.
Mix 2 teaspoons of flour in a little water and add to the pot.
Stir in a small piece of butter 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.

Flour + buttertop 12% of all pairs

Smell alikelow

Cooked together124,287 recipes

Shared aroma: isobutyraldehyde (malty, green).
Onion + buttertop 15% of all pairs

Smell alikemoderate

Cooked together42,912 recipes

Shared aroma: decanal (soap, orange peel).
Onion + flourtop 17% of all pairs

Smell alikemoderate

Cooked together32,460 recipes

Shared aroma: isobutyraldehyde (malty, green).

Flour and butter barely smell alike, yet cooks put them together in 124,287 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

Onion: Softens as it simmers, releasing its flavour into the water to form the soup base.
Flour: Thickens the liquid as it is stirred in, giving the soup body.
Butter: Adds richness and a smooth fat note to the finished soup.