blanch
Briefly boil, then immediately transfer to ice water to stop the cooking. Used to partially cook vegetables while preserving color and crispness, or to loosen skins for peeling.
How to do it
Bring a generous amount of water to a strong boil, and salt it if the vegetable will actually be eaten rather than just peeled. Add the food without overloading the pot -- too little water means the temperature drops sharply the moment the food goes in, and it needs to come back to a boil quickly. Cook only until it reaches the point you're after, then, if the process needs to stop, transfer the food immediately into a large bowl of ice and cold water. Once it's fully cool, drain it thoroughly -- leaving vegetables sitting in the ice bath indefinitely waterlogs them.
Common pitfalls
- Too little water -- adding the food drops the temperature dramatically and slows everything down.
- Overcooking -- without watching the clock, a blanch turns into a full boil.
- Not enough ice -- lukewarm water doesn't actually stop the cooking.
- Leaving food in the ice bath too long -- cooling should be quick, not indefinite.
- Skipping the dry-off afterward -- leftover surface water works against a later roast or sauté.
Why it works
Heat softens plant tissue partly by changing cell-wall materials like pectin. Green vegetables also contain chlorophyll, and brief cooking can make their color look especially vivid as gas trapped between the cells escapes and the tissue turns slightly more translucent -- but prolonged heat, especially with any acidity, converts that same chlorophyll into duller, olive-colored compounds. Rapid cooling in the ice bath slows those reactions down before they go further than intended. For skinning tomatoes or peaches, the same brief heat weakens the tissue just under the skin enough that it slips off easily.
Equipment
Use a large pot so the water temperature stays relatively stable when food goes in. A wire skimmer, spider, or slotted spoon makes it easy to pull food out quickly; for larger batches, a removable basket insert helps. Set up the ice bath before the food goes into the boiling water, not after.