Blanching is a cooking process wherein the food substance, usually a vegetable or fruit, is scalded in boiling water, removed after a brief, timed interval, and finally plunged into iced water or placed under cold running water (shocking or refreshing) to halt the cooking process. There are two main blanching techniques including steam blanching and water-submersion blanching.
The meaning of blanch is "to whiten", but this is not always the purpose of blanching in cooking. Food is blanched to soften it, or to partly or fully cook it, or to remove a strong taste (for example of cabbage or onions).
Blanching is used for a variety of reasons commercially for economic and quality improvement of the product. Blanching is affected by factors such as Temperature and Time, which can have major organoleptic changes to the product if under-processed or over-processed. One of the cardinal uses of blanching is enzyme inactivation in green peas, green bean, carrots etc,. Catalase, peroxidase, lipoxygenase, polyphenoloxidase are some of the commonly inactivated enzymes taken into consideration during processing.   These enzymes are attributed to the loss of flavor, color, texture and nutritional qualities during product storage.  Moreover, due to the heat treatment, intercellular gases are removed which results in color retention. This can be credited towards the change in the wavelength of reflected light. Food is also blanched to soften vegetable tissues in order to facilitate packaging. During the process, surface contaminants are removed with certain types of blanching methods such as water blanching. Bacterial inactivation occurs during the process, however its not considered to be the most efficient at it and is combined with other technologies for sterilization to increase product shelf-life.
Blanching may simply mean boiling in water for an extended period to remove unpleasant flavours such as tannins. For example, a recommended treatment for African yam bean (Sphenostylis stenocarpa), is dehulling followed by blanching in water for 40 minutes at 100 °C.
It is recommended that protein-rich salads to be eaten cold (e.g., tuna, turkey, ham, shrimp, lobster, and chicken) be prepared by immersing these protein foods in boiling water for 30 seconds followed by fast chilling. In addition celery, "which is almost always a component of these salads…should be treated so as to minimize its bacterial content".
In the case of French fries, blanching consists of pre-cooking the French fries in oil at a lower temperature prior to finishing them at a higher temperature. The blanching step cooks the interior of the potato, while the second step at the higher temperature crisps the outside.
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