"To blanch" means to very briefly cook vegetables (sometimes fruit) in boiling water. You can also steam or microwave, but boiling water is the usual method at home. (Though some of my acquaintances have ex's who can make vegetables blanch just by looking at them.)
Blanch can also be used in a sense that is actually much closer to what it really means, which is to "make white." It's the process by which produce such as Belgian Endive, White Asparagus, Seakale and Champagne Rhubarb are grown, deprived of light, so that they don't develop any colour.
Blanching in the kitchen can be done for varying reasons:
- Prepare vegetables for freezing and longer storage life. The scalding destroys enzymes which are otherwise "programmed" to decompose the produce and destroy its nutritional value and eventually its appearance and texture;
- Make it easier to peel some items (such as almonds, peaches and tomatoes);
- Develop a bit of taste in a vegetable otherwise intended to be served raw (this is also called parboiling);
- Make the taste of produce such as garlic or kale milder, or to make meats such as salt pork or bacon less salty.
Onions, mushrooms and green peppers don't need to be blanched before freezing.
You don't want to under blanch or over blanch; times vary according to what you are processing. Put vegetables into water that is already boiling. So that the water doesn't stop boiling when you add the vegetables, use about 1 gallon of water per 1 pound of prepared vegetables (4 litres of water per 450g of veg.) Cover and start counting the blanching time from when the water returns to a full boil. When the time is up, remove with a slotted spoon or drain them by another method, and plunge them into a sink (or other container) full of water as cold as you can get it. Allow the veg to chill for a number of minutes equal to the time that you blanched them for, then drain, pack and freeze.
Steam blanching is recommend for more delicate items such as grated zucchini or sprouts.
Some university research has found that microwave blanching doesn't always destroy all the enzymes that should be rendered ineffective before freezing vegetables. The studies did find, however, that in terms of energy being used (not counting your own physical exertion, of course), there are no energy savings to be realized by microwaving versus boiling.
"Oh look, we have created enchantment". Blanche DuBois in A Streetcar Named Desire, 1951(written by Tennessee Williams).
Literature & Lore
From the French verb, "blanchir", which means to turn white. The verb in turn comes from the French word for white, blanc (in fact, the feminine version of the word, which is "blanche".)
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Blanchir (French); Blanchieren (German); Escaldar (Spanish); Aquecer (Portuguese)