Raw onions can overpower a salad or sandwich with a sharp taste that lingers after each bite. Red onions, in particular, can have enough pungency to compete with the other ingredients. One preparation step involves soaking the sliced onions in cold water before adding them to a dish.
Cold water helps remove some of the sulfur-containing compounds responsible for the sharp flavor. These compounds develop when an onion is cut, triggering reactions between substances stored in separate parts of its cells.
The method takes about 10 to 15 minutes and doesn’t require cooking, salt, or vinegar. The onions retain their crunch while losing some of the harshness that makes raw slices difficult to eat.
Cold Water Reduces Some of the Compounds Behind Onion Sharpness
Onions contain sulfur compounds and enzymes stored in different parts of their cells.
Cutting or slicing an onion damages those cells, allowing the enzymes to react with sulfur-containing substances.
These reactions produce compounds responsible for the onion’s pungent smell, sharp taste, and eye irritation during cutting.
Some of the compounds and their reaction products can move into water when the sliced onion is submerged.
Soaking helps wash away part of the material responsible for the sharp bite, reducing its intensity without cooking the onion.
Cold water also keeps the slices firm, unlike heat, which softens onion tissue and changes its flavor.
The effect depends on onion variety, slice thickness, and soaking time. A strong yellow onion may retain more pungency than a mild sweet onion after the same treatment.
Soaking doesn’t remove every sulfur compound or eliminate the onion’s flavor. It reduces some of the sharpness while preserving the raw texture.
How to Soak Raw Onions Before Adding Them to Food
Start with one red, white, or yellow onion and remove the outer skin.
Slice the onion into thin rings or half-moons, keeping the pieces close in thickness.
Place the slices in a bowl and cover them with cold water.
Let them soak for 10 to 15 minutes, keeping the bowl refrigerated if preparing the onions ahead of serving.
Drain the water and rinse the slices once under fresh cold water.
Transfer them to a clean kitchen towel or paper towels and remove excess moisture before adding them to food.
Drying prevents water from diluting salad dressings or making sandwich bread damp.
For a stronger onion, taste a piece after the first soak. If the flavor remains too sharp, another short soak may reduce it further, although some onion flavor will also be lost.
Use the drained slices in salads, burgers, sandwiches, tacos, or other dishes where raw onion provides crunch.
The technique works best when the goal is to soften the onion’s pungency without changing its texture through cooking or pickling.
Cold water removes some of the compounds responsible for an onion’s sharp bite, leaving the slices crisp but less pungent when served raw.
Sources: Library of Congress — Why Do Onions Make You Cry?, Encyclopaedia Britannica — Onion, National Onion Association
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