Name: An Old Recipe for Tomato Catsup
Ingredients: ½ bushel skimmed tomatoes; 1 quart best cider vinegar; 2 pounds brown sugar; 1 pound coarse sea salt; 6 large onions, sliced; ½ pound black pepper; ½ pound allspice (whole grains); ½ pound English mustard; ½ pound whole cloves; ½ ounce cayenne pepper; a handful of peach leaves, washed; a little fresh grated horseradish

Why it works: Allspice and mustard match in chemistry and in kitchens. They rank in the top 2% of all ingredient pairs, and cooks put them together in 1,928 recipes. Both carry methyleugenol, which smells clove, spice. The science ↓

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.

Allspice + mustardtop 2% of all pairs

Smell alikestrong

Cooked together1,928 recipes

Shared aroma: methyleugenol (clove, spice).
Pepper + allspicetop 5% of all pairs

Smell alikestrong

Cooked together6,395 recipes

Shared aroma: estragole (anise, licorice).
Onion + mustardtop 6% of all pairs

Smell alikestrong

Cooked together9,259 recipes

Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
Cider + vinegartop 6% of all pairs

Smell alikemoderate

Cooked together3,431 recipes

Shared aroma: 4-ethyl-2-methoxyphenol (smoky, clove).
Tomato + peppertop 7% of all pairs

Smell alikemoderate

Cooked together17,923 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

Skimmed tomatoes: Provide the main body, moisture and tomato flavour of the ketchup.
Cider vinegar: Adds acidity that sharpens flavour and helps preserve the finished sauce.
Brown sugar: Adds sweetness and depth, and helps balance the acidity of the vinegar.
Onions: Contribute body and savoury sweetness as they break down during boiling.

The step that matters

Boil for 3 hours, stirring often. Long simmering thickens the sauce by evaporating water, but the sugars and tomato solids can scorch on the bottom of the pot. Frequent stirring prevents burning and keeps the flavour clean.

Swap the onion

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

Capsicumfits better
Horseradishfits better
Cucumberfits better
Onionthe original

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

An Old Recipe for Tomato Catsup