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Tomato Catsup

A homemade tomato-based condiment made by cooking tomatoes, onions, peppers, and spices, then thickening and bottling.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 9 ingredients
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Why it works: Onion and mustard 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 Catsup

Ingredients

Directions

Make the base

  1. In a porcelain kettle, combine the quartered tomatoes, sliced onions, and chopped peppers.

  2. Boil the mixture until perfectly done.

  3. Strain through a coarse sieve, mashing all the pulp through.

Season and thicken

  1. To the resulting juice, add the cider vinegar, coarse sea salt, mustard, ground black pepper, and sugar to taste.

  2. Boil the mixture until it thickens.

Bottle

  1. Bottle and seal the catsup.

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

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

  4. Vinegar + mustardtop 7% of all pairs
    Smell alikemoderate
    Cooked together14,067 recipes

    Shared aroma: isobutyraldehyde (malty, green).

  5. Tomato + oniontop 8% of all pairs
    Smell alikemoderate
    Cooked together20,633 recipes

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

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

What each ingredient does

Tomatoes
Provide the main body, pulp and flavor of the ketchup.
Onions
Add savory depth and aroma to the cooked base.
Cider vinegar
Adds acidity that sharpens flavor and helps preserve the ketchup.
Green peppers
Contribute vegetal flavor and aroma to the cooked mixture.
Red peppers
Add sweetness and color along with additional pepper flavor.

The step that matters

Boil until it thickens. Cooking the strained juice down reduces its water content and concentrates the flavor. Undercooking leaves the ketchup thin, while overcooking can make it too dense or scorch it on the bottom of the pan.

Swap the onion

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

  1. Capsicumfits better
  2. Cucumberfits better
  3. Horseradishfits better
  4. Onionthe original

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

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