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Processing Onions

A method for preserving onions using alum, salt, and vinegar.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 5 ingredients
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Processing Onions

Ingredients

Directions

Prepare the brine

  1. Place the onions in a large tank.

  2. Add 2 pounds of alum to 50 gallons of cold fresh water.

  3. Heat the mixture to 100°F (38°C), ensuring it does not exceed 110°F (43°C).

Soak and peel

  1. Let the onions soak for 24 hours.

  2. Transfer the onions to cold fresh water and let them sit for 2 to 3 days until peeled.

Preserve

  1. After peeling, place the onions in a cask and cover with water mixed with 1 pound of powdered alum or 5 pounds of salt if not using alum.

  2. After 2 days, drain the onions and cover them with 40 grain vinegar.

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

What each ingredient does

Alum
Firms the onion tissue so the onions stay crisp during long soaking.
Salt
Draws water out of the onions and inhibits spoilage microbes as an alternative to alum.
Vinegar
Adds acidity that preserves the onions and gives them a sharp flavor.

The step that matters

Keeping the alum solution between 100°F and 110°F. The record sets a target of 100°F and a ceiling of 110°F. Holding the solution in this range keeps the alum working evenly on the onions without overheating and softening them.

“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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