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[1]) to halt the cooking process. There are two main blanching techniques including steam blanching and water-submersion blanching.[2]

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).[3]

When almonds or pistachios are blanched, the skin of the nut (botanically the seed coat surrounding the embryo) softens and can be easily removed later.


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,.[4] Catalase, peroxidase, lipoxygenase, polyphenoloxidase are some of the commonly inactivated enzymes taken into consideration during processing. [4] [5] These enzymes are attributed to the loss of flavor, color, texture and nutritional qualities during product storage. [6] Moreover, due to the heat treatment, intercellular gases are removed which results in color retention.[7] 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.

Other definitions

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.[8]

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.[9] In addition celery, "which is almost always a component of these salads…should be treated so as to minimize its bacterial content".[9]

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.[10]

See also


  • Desrossier, NW, The technology of food preservation, The AVI Publishing Company, 1965, p. 150–151
  1. ^ Ruhlman, Michael. 2013
  2. ^ Fellows, P.J. (2009). Food processing technology (3rd ed.). Woodhead Publishing Limited. p. 371. ISBN 978-1-84569-216-2. 
  3. ^ Child, J.; Bertholle, L.; Beck, S. 1961, 1983, 2001. Mastering the art of French cooking. Alfred A. Knopf.
  4. ^ a b "Peroxidase and Lipoxygenase Inactivation During Blanching of Green Beans, Green Peas and Carrots". LWT - Food Science and Technology. 26 (5): 406–410. 1993-10-01. doi:10.1006/fstl.1993.1080. ISSN 0023-6438. 
  5. ^ "Steam blanching effect on polyphenoloxidase, peroxidase and colour of mango (Mangifera indica L.) slices". Food Chemistry. 113 (1): 92–95. 2009-03-01. doi:10.1016/j.foodchem.2008.07.027. ISSN 0308-8146. 
  6. ^ "Effects of polyphenol oxidase and peroxidase activity, phenolics and lignin content on the browning of cut jicama". Postharvest Biology and Technology. 33 (3): 275–283. 2004-09-01. doi:10.1016/j.postharvbio.2004.03.009. ISSN 0925-5214. 
  7. ^ Krokida, M; Kiranoudis, Chris; Maroulis, Zacharias; Marinos-Kouris, D (2000-07-01). "Effect of pretreatment on color of dehydrated products". Drying Technology. 18: 1239–1250. doi:10.1080/07373930008917774. 
  8. ^ Aminigo ER, Metzger LE: Pretreatment of African yam bean (Sphenostylis stenocarpa), effect of soaking and blanching on the quality of African yam bean seed [1]
  9. ^ a b "Food Protection Training Manual" (PDF). New York City Department of Health & Mental Hygiene. 2010. 
  10. ^ Blumenthal, Heston (17 April 2012). "How to cook perfect spuds". the age. Retrieved 12 October 2012.