Blanching in Cooking and Food Preservation

Blanching tomatoes
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The word blanch refers to a cooking technique in which food is briefly immersed in steam or boiling water or fat, usually followed by shocking, which is rapidly cooling the food in an ice bath or with cold air. Blanching is used both in cooking and in preparing vegetables and fruits for preservation. When you blanch a food for the right amount of time you help maintain flavor, color, texture, and nutritional value before canning or freezing. It also helps soften the food items and loosens skin to assist in peeling. Blanching is used both by home cooks and in industrial food processing.

The Blanching Process

When you see a recipe instruction to blanch a vegetable or fruit, note the length of time suggested for blanching and whether to use salted water (which is primarily done for seasoning). Recipes may or may not explicitly say to shock the food items after blanching, but that is usually desired.

Here is how to blanch:

  1. Set a large pot of water to boil.
  2. Once it is boiling, immerse the vegetable or fruit in the boiling water and return the pot to a boil.
  3. Once the water is boiling again, begin timing for the length of blanching recommended, usually just a couple of minutes.
  4. At the end of that time, remove the food items from the boiling water and plunge them into an ice water bath.
  5. As soon as they're cool, drain them and set them aside either to use in a recipe or to process for canning or freezing.

The Chemistry of Blanching

Blanching begins the cooking process but ends it at just the desired point. As long as something is hot, it's cooking. All the molecular and other changes that result from this are happening—vegetable fibers soften, pigments change color, and enzymes (which are proteins) are inactivated. Because vegetables and fruits are delicate, cooking them for two minutes instead of one can turn them limp, soggy and drab.

Plunging the food items into an ice water bath halts the cooking process. Ice water works best because it cools quickly. Even a few cubes from your ice tray will make a difference. But if all you have is cold tap water, then use that. It helps to run the tap for a few seconds until the water runs cooler. However, leaving the food items in the ice bath for too long will turn them soggy as well. Be sure to drain the veggies completely after shocking them.

Uses of Blanching

Blanching vegetables soften them just enough so that they can then be quickly cooked over high heat, such as in a stir-fry. A short time in the pan wouldn't be enough to soften vegetables, but cooking them longer would tend to overcook the other items in the pan. In this case, you wouldn't shock the vegetables after blanching them.

Blanching and shocking is a good technique to use for vegetables that will be featured in salads. They're softened just enough so that you can eat them more or less raw, but they won't be excessively difficult to chew. Think of carrots or broccoli in that regard.

Vegetables such as green beans are often blanched in order to enhance their natural green color, as well as softening them. You'd want to blanch and shock green beans before using them in a Niçoise salad, for example.

Another use for blanching is to help loosen the skins on tomatoes, peaches, and other foods. If you make your own marzipan, you need to blanch the almonds to remove their skins. Also, when preparing white stocks such as chicken or veal stock, the bones are blanched beforehand in order to rid them of impurities.

When making french fries, the cut potatoes are often blanched in medium-heat oil and then cooled before frying them a second time at a higher temperature. Believe it or not, blanching is also an excellent technique for preventing avocados from turning brown.