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 ↓
Tomato Soup
Ingredients
Directions
Make the soup
In a bowl, rub together the flour and butter with 1 tablespoon of tomato.
In a pot, bring the hot water to a boil and add the canned tomatoes, salt, and sugar.
Stir in the flour and butter mixture, and boil for 15 minutes.
Finish and serve
Rub the soup through a sieve and serve with toast crumbs.
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.
Photo for illustrative purposes only · Contact us to use it
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 pairsSmell alikelowCooked together124,287 recipes
Shared aroma: isobutyraldehyde (malty, green).
-
Flour + sugartop 15% of all pairsSmell alikemoderateCooked together92,116 recipes
Shared aroma: phenylacetaldehyde (hawthorne, honey).
-
Butter + sugartop 17% of all pairsSmell alikemoderateCooked together98,233 recipes
Shared aroma: guaiacol (smoky, sweet).
-
Tomato + buttertop 22% of all pairsSmell alikemoderateCooked together6,918 recipes
Shared aroma: 3-hexenal (apple, fruity).
-
Tomato + flourtop 22% of all pairsSmell alikemoderateCooked together7,065 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
- Canned tomatoes
- Form the body and the tangy, acidic flavour of the soup.
- Flour
- Thickens the soup as its starch cooks in the hot liquid.
- Butter
- Adds fat that enriches the flavour and helps the flour blend smoothly.
- Sugar
- Softens the tomato's acidity with a small amount of sweetness.
The step that matters
Stir in the flour and butter mixture. Flour clumps if it is not dispersed evenly into the liquid. Boiling the mixture for the full 15 minutes cooks the starch, which thickens the soup and removes the raw floury taste.
Swap the tomato
How well each one fits the dish's main ingredients (flour, butter, sugar):
- Arrowrootfits better
- Shallotfits better
- Sweet potatofits better
- Tomatothe original
Fit is the average pairing score against flour, butter, sugar. 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.
More tomato soup recipes
You might also like
The free Flavor Lab newsletter: one surprising pairing a week and the molecular reason it works, in 60 seconds. No spam, unsubscribe anytime.
Prefer an account? Create a free account to save pairings and unlock the full chemistry.

Tomato Bisque61 recipes
Tomato Fritters23 recipes
Tomato Puree23 recipes
Macaroni with Tomato Sauce16 recipes