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Dessert

Boiled Icing

A boiled sugar icing made with sugar, water, egg whites, and lemon juice.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 4 ingredients
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Why it works: Sugar and lemon are a kitchen classic. They rank in the top 18% of all ingredient pairs, and cooks put them together in 53,532 recipes. Both carry 2-nonenal, which smells fatty, green. The science ↓

Boiled Icing

Ingredients

Directions

Make the syrup

  1. Combine sugar and water in a saucepan.

  2. Boil until it forms threads when dropped from a spoon or hardens in cold water.

Make the icing

  1. Beat the egg whites to stiff peaks.

  2. Stir the egg whites into the sugar mixture briskly for a few minutes until smooth.

  3. Add the lemon juice and mix well.

Use

  1. Use the icing to fill between layers of a medium-sized cake or to frost the top and sides.

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. Sugar + lemontop 18% of all pairs
    Smell alikelow
    Cooked together53,532 recipes

    Shared aroma: 2-nonenal (fatty, green).

  2. Egg + lemontop 19% of all pairs
    Smell alikelow
    Cooked together44,316 recipes

    Shared aroma: (e,e)-2,4-decadienal (fatty, deep fried).

  3. Sugar + eggtop 21% of all pairs
    Smell alikemoderate
    Cooked together122,807 recipes

    Shared aroma: 2-nonenal (fatty, green).

Sugar and lemon barely smell alike, yet cooks put them together in 53,532 recipes: they work on texture and structure more than aroma.

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

What each ingredient does

Sugar
Forms the syrup that sets into a glossy, sweet icing structure.
Egg whites
Whipped to stiff peaks, they add airy volume and body to the icing.
Lemon juice
Adds acidity that balances the sweetness and helps keep the icing stable.

The step that matters

Boiling the sugar syrup to the right stage. Sugar syrup must reach the correct concentration to set properly. Boiling too little leaves the icing runny, while boiling too long makes it hard and grainy once cooled.

Swap the lemon

How well each one fits the dish's main ingredients (sugar, egg):

  1. Vanillafits better
  2. Raisinfits about as well
  3. Lemonthe original
  4. Datesfits less well

Fit is the average pairing score against sugar, egg. 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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