Name: Cold Catsup
Ingredients: 8 ripe tomatoes; 6 cups sugar; 5 green peppers; ½ cup whole mustard; 5 onions; 1 quart vinegar (scant); ½ cup coarse sea salt (formerly 'bay salt')

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 ↓

Cold Catsup

Ingredients

Directions

Peel the tomatoes, chop them, and drain well.
Remove seeds from the peppers, chop them, and chop the onions.
Mix all ingredients together.
This catsup is ready for use at any time.

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.

Mustard + oniontop 6% of all pairs

Smell alikestrong

Cooked together9,259 recipes

Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
Tomato + peppertop 7% of all pairs

Smell alikemoderate

Cooked together17,923 recipes

Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
Mustard + vinegartop 7% of all pairs

Smell alikemoderate

Cooked together14,067 recipes

Shared aroma: isobutyraldehyde (malty, green).
Tomato + oniontop 8% of all pairs

Smell alikemoderate

Cooked together20,633 recipes

Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
Pepper + mustardtop 9% of all pairs

Smell alikemoderate

Cooked together15,430 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 and fresh tomato flavour of the catsup.
Sugar: Adds sweetness and balances the sharpness of the vinegar.
Vinegar: Adds acidity that gives the catsup its tang and helps preserve it.
Green peppers: Add a grassy, slightly bitter vegetable flavour and crisp texture.
Onions: Add savoury depth and aroma to the catsup.
Whole mustard: Adds sharp, pungent flavour that complements the tomatoes and vinegar.

Swap the tomato

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

Horseradishfits better
Capsicumfits better
Broccolifits better
Tomatothe original

Fit is the average pairing score against sugar, pepper, mustard, onion, 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.