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Tomato Ketchup

A homemade tomato ketchup made by boiling tomatoes, spices, onions, and vinegar.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 8 ingredients
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Why it works: Mustard and onion match in chemistry and in kitchens. They rank in the top 6% of all ingredient pairs, and cooks put them together in 9,259 recipes. Both carry 2-isopropyl-3-methoxypyrazine, which smells earthy, pea. The science ↓

Tomato Ketchup

Ingredients

Directions

  1. Boil the ripe tomatoes for one hour and strain through a sieve.

  2. To the quart of juice, add cinnamon, black pepper, cayenne, ground mustard, coarse sea salt, and chopped onions.

  3. Boil the mixture for three hours.

  4. Add one pint of cider vinegar to each quart of juice and boil for an additional half hour.

  5. Bottle the ketchup while hot.

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. Mustard + oniontop 6% of all pairs
    Smell alikestrong
    Cooked together9,259 recipes

    Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).

  2. Cider + vinegartop 6% of all pairs
    Smell alikemoderate
    Cooked together3,431 recipes

    Shared aroma: 4-ethyl-2-methoxyphenol (smoky, clove).

  3. Cinnamon + mustardtop 7% of all pairs
    Smell alikestrong
    Cooked together1,581 recipes

    Shared aroma: guaiacol (smoky, sweet).

  4. Tomato + peppertop 7% of all pairs
    Smell alikemoderate
    Cooked together17,923 recipes

    Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).

  5. Mustard + vinegartop 7% of all pairs
    Smell alikemoderate
    Cooked together14,067 recipes

    Shared aroma: isobutyraldehyde (malty, green).

Ranks compare each pair with 20,000 random ingredient pairs on CompKitchen. How we score pairs

What each ingredient does

Ripe tomatoes
Provide the main body, liquid and flavour of the ketchup once cooked down.
Onions
Add savoury depth and body as they soften during the long simmer.
Cider vinegar
Adds acidity that sharpens flavour and helps keep the finished ketchup stable.
Coarse sea salt
Seasons the sauce and draws out flavour from the tomatoes and spices.

The step that matters

Boiling the mixture for three hours. Long simmering evaporates water and concentrates the tomato solids, so the sauce thickens and its flavours deepen. Stopping early leaves it thin and watery.

Swap the cinnamon

How well each one fits the dish's main ingredients (tomato, pepper, mustard, onion, cider, vinegar):

  1. Garlicfits better
  2. Thymefits better
  3. Tarragonfits better
  4. Cinnamonthe original

Fit is the average pairing score against tomato, pepper, mustard, onion, cider, vinegar. 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.

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