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Lentil Soup

A hearty soup of lentils simmered with onion, bay leaf, and water, finished with a butter‑flour roux, salt, and lemon juice.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 8 ingredients
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Why it works: Lentils and flour match in chemistry and in kitchens. They rank in the top 5% of all ingredient pairs, and cooks put them together in 255 recipes. Both carry isobutyraldehyde, which smells malty, green. The science ↓

Lentil Soup

Ingredients

Directions

Cook the lentils

  1. Combine lentils, bay leaf, onion, and water in a pot.

  2. Bring the mixture to a boil.

  3. Reduce heat and simmer for three hours, or until lentils are tender.

  4. Strain the mixture through a colander.

Thicken and finish

  1. Rub together flour and butter in a bowl.

  2. Stir in a little of the soup.

  3. Add the roux back to the pot.

  4. Boil for five minutes.

  5. Add salt and lemon juice just before serving.

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.

  1. Lentils + flourtop 5% of all pairs
    Smell alikestrong
    Cooked together255 recipes

    Shared aroma: isobutyraldehyde (malty, green).

  2. Lentils + oniontop 8% of all pairs
    Smell alikestrong
    Cooked together1,221 recipes

    Shared aroma: coumarin (sweet, hay).

  3. Lentils + lemontop 11% of all pairs
    Smell alikestrong
    Cooked together249 recipes

    Shared aroma: coumarin (sweet, hay).

  4. Flour + buttertop 12% of all pairs
    Smell alikelow
    Cooked together124,287 recipes

    Shared aroma: isobutyraldehyde (malty, green).

  5. Butter + oniontop 15% of all pairs
    Smell alikemoderate
    Cooked together42,912 recipes

    Shared aroma: decanal (soap, orange peel).

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

Dry lentils
Main body of the soup; they soften during simmering and thicken the broth as they break down.
Flour
Thickens the soup when cooked with butter into a roux and stirred into the liquid.
Butter
Combined with flour to form a roux, which helps thicken the soup smoothly and adds richness.
Lemon juice
Adds acidity that brightens the flavour of the soup.

The step that matters

Stir the roux into a little soup before adding it to the pot. Flour dropped straight into hot liquid clumps as its starch grains swell unevenly. Thinning the roux with some hot soup first lets it disperse smoothly, so the soup thickens without lumps.

Swap the lemon

How well each one fits the dish's main ingredients (lentils, flour, butter, onion):

  1. Avocadofits better
  2. Coconutfits better
  3. Limefits better
  4. Lemonthe original

Fit is the average pairing score against lentils, flour, butter, onion. 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 lentil soup recipes

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