Why it works: Milk and butter are a kitchen classic. They rank in the top 7% of all ingredient pairs, and 81,283 recipes mention both. Both carry (z)-4-heptenal, which smells biscuit, cream. The science ↓
Tomato Soup
Ingredients
Directions
Make the tomato stock
Place fresh tomatoes in a saucepan with 1 quart of water; if using canned tomatoes, use slightly more than 1 pint.
Add peppercorns and onion, and boil for 30 minutes.
Add baking soda and strain through a sieve.
Finish the soup
In another saucepan, boil the milk and butter.
Thicken the milk mixture with flour until it resembles cream.
Once boiling, add the tomato stock and boil again.
Season with salt and serve.
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 aroma chemistry they share, and how many recipes mention both.
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Milk + buttertop 7% of all pairsAroma overlapmoderateMentioned together81,283 recipes
Shared aroma: (z)-4-heptenal (biscuit, cream).
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Tomato + oniontop 8% of all pairsAroma overlapmoderateMentioned together20,633 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Butter + flourtop 12% of all pairsAroma overlaplowMentioned together124,287 recipes
Shared aroma: isobutyraldehyde (malty, green).
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Milk + flourtop 14% of all pairsAroma overlaplowMentioned together78,219 recipes
Shared aroma: isobutyraldehyde (malty, green).
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Butter + oniontop 15% of all pairsAroma overlapmoderateMentioned together42,912 recipes
Shared aroma: decanal (soap, orange peel).
Butter and flour share little aroma chemistry, yet 124,287 recipes mention both: they likely 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
- Tomatoes
- Provide the main flavour and the soup's base, with natural acidity.
- Milk
- Gives the soup its creamy body and mild sweetness.
- Flour
- Thickens the milk mixture so the soup becomes creamy rather than watery.
- Butter
- Adds fat for richness and a smoother mouthfeel.
- Baking soda
- Neutralises some of the tomato acidity, making the soup taste less sharp.
The step that matters
Adding the tomato stock to the milk mixture. Tomato is acidic, and acid combined with heat can curdle milk proteins, leaving a grainy soup. Baking soda in the stock neutralises some of that acid, and the milk mixture should be boiling but thickened first so it can hold together when the stock is added.
Flavor stand-ins for the onion
How well each one fits the dish's main ingredients (tomato, milk, butter, flour):
- Potatobetter flavor fit
- Capsicumbetter flavor fit
- Okrabetter flavor fit
- Onionthe original
Fit is the average pairing score against tomato, milk, butter, flour. Candidates are from the same food group and used in at least 100 recipes. This compares flavor only: it does not check the job the ingredient does in the dish (bulk, moisture, acidity, structure).
“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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