Name: Cucumber Catsup
Ingredients: 12 large ripe cucumbers; 10 small onions; 2 tablespoons grated horseradish; ½ teaspoon cayenne pepper; 1 teaspoon white sugar; ¼ teaspoon salt; ¼ teaspoon black pepper; cold vinegar; ½ teaspoon mustard (optional)

Why it works: Horseradish and mustard match in chemistry and in kitchens. They rank in the top 1% of all ingredient pairs, and cooks put them together in 1,832 recipes. Both carry coumarin, which smells sweet, hay. The science ↓

Cucumber Catsup

Ingredients

Directions

Prepare

Pare the cucumbers and remove the seeds.
Grate the cucumbers finely.

Make the ketchup

In a bowl, combine the grated cucumbers, chopped onions, horseradish, cayenne pepper, sugar, salt, and black pepper.
Cover the mixture with cold vinegar and seal the container.
Add mustard for improved flavor, if desired.

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.

Horseradish + mustardtop 1% of all pairs

Smell alikestrong

Cooked together1,832 recipes

Shared aroma: coumarin (sweet, hay).
Cucumber + horseradishtop 2% of all pairs

Smell alikestrong

Cooked together640 recipes

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

Smell alikestrong

Cooked together2,281 recipes

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

Smell alikestrong

Cooked together9,259 recipes

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

Smell alikestrong

Cooked together1,784 recipes

Shared aroma: coumarin (sweet, hay).

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

What each ingredient does

Cucumbers: Form the bulk of the ketchup, providing moisture and a fresh, watery base.
Onions: Add pungent savoury flavour and aroma that balances the cucumber.
Horseradish: Contributes sharp pungency that gives the ketchup its bite.
Vinegar: Acts as the acidic liquid that preserves the mixture and adds tang.

“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.