Flash freezing

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Flash freezing refers to the process in various industries whereby objects are quickly frozen by subjecting them to cryogenic temperatures, or in direct contact with liquid nitrogen at -196°C.

Flash freezing is used in the food industry to quickly freeze perishable food items (see frozen food). In this case, food items are subjected to temperatures well below water's melting/freezing point. The freezing process results in ice crystals formed from intra- and extracellular water, and subsequent crystal growth. The freezing speed directly influences the nucleation process and ice crystal size. Decreased growth of the initially formed ice crystals is a result of a high heat removal rate and causes an increased rate of nucleation. Smaller, more ubiquitous ice crystals cause less damage to cell membranes. [1]

Flash freezing techniques are also used to freeze biological samples fast enough that large ice crystals cannot form and damage the sample.[2] This rapid freezing is done by submerging the sample in liquid nitrogen or a mixture of dry ice and ethanol.[3]

A supercooled liquid will stay in a liquid state below the normal freezing point when it has little opportunity for nucleation; that is, if it is pure enough and has a smooth enough container. Once agitated it will rapidly become a solid.

American inventor Clarence Birdseye developed the quick-freezing process of food preservation in the 20th century.[4]

This process was further developed by American inventor Daniel Tippmann[5] by producing a vacuum and drawing the cold air through palletized food. His process has been sold and installed under the trade name "QuickFreeze" [6] and enables blast freezing of palletized food in 35% less time than conventional blast freezing.[7]

References[edit]

  1. ^ Da-Wen Sun (2001), Advances in food refrigeration, Yen-Con Hung, Cryogenic Refrigeration, p.318, Leatherhead Food Research Association Publishing, http://www.worldcat.org/title/advances-in-food-refrigeration/oclc/48154735
  2. ^ "Freezing Tissue". Biotech.ufl.edu. Retrieved 2009-07-03. 
  3. ^ "Preparing Competent E. coli with RF1/RF2 solutions". Personal.psu.edu. Retrieved 2009-07-03. 
  4. ^ "Quick-Frozen Food Exactly Like Fresh." Popular Science Monthly, September 1930, pp. 26-27.
  5. ^ http://www.google.com/patents/US20110107784
  6. ^ http://www.tippmannengineering.com/quickfreeze
  7. ^ http://www.gcca.org/cold-facts/cover-story-innovation-on-display.html