Blanching is a cooking technique often used in tandem with other techniques for a variety of reasons. Blanching is an important part of preparing fresh vegetables before freezing them. Sometimes, it's used to remove undesirable flavors from foods before using them in a recipe, or to soften and separate the skins from fruits and nuts.
In food science blanching is the process of quickly and minimally cooking food in boiling water or, sometimes, hot fat. The food is usually only submerged for two to three minutes, though longer times may be necessary for denser foods. Food blanched in boiling water is most often used in conjunction with shocking, or immediately placing the blanched food in cold water or an ice bath to halt the cooking process.
Reasons for Blanching
Especially in the case of vegetables that are to be frozen, blanching brings out the flavor of the food while maintaining its color, texture and nutritional qualities. For a quick snack, blanching vegetables enhances the flavor of raw vegetables without making them too soft. Blanching can also be used to aid in peeling the outer skin from fruits, nuts or vegetables before adding them to a recipe.
Function of Blanching
Scientifically, the high heat from the boiling water begins breaking down the cell walls of the vegetable. According to Alan Davidson in "The Oxford Companion to Food," this deactivates enzymes in the vegetable that would cause it to continue breaking down once it's frozen. Blanching also removes excess gases from the plant tissues resulting in less oxidation in food as it freezes. This is how blanching works to preserve the color, texture, flavor and nutrition of vegetables before they're frozen.
When blanching vegetables to be frozen, cut them into uniform pieces. This facilitates even cooking so smaller pieces don't accidentally get overcooked. Place the cut vegetables in a wire basket and place in a pot of boiling water. Different vegetables have different blanching times so be sure to blanch them separately. Start with those lighter in color, as colors transferred to the blanching water can soak into lighter-colored foods. It's a good idea to consult a food blanching chart like the one by Carol Burtness, University of Minnesota extension educator, on the school's website, where you can find suggested blanching times for many kinds of vegetables and beans. See chart under Resources, below.
- University of Wisconsin Madison: Preservation by Heat
- University of Minnesota Extension: Food Safety, Blanching Vegetables
- NNY Living: Master the Art of Blanching Vegetables
- The Oxford Companion to Food; Alan Davidson
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