Flash freezing

Flash freezing refers to the process in various industries whereby objects are frozen in a few hours by subjecting them to cryogenic temperatures, or in direct contact with liquid nitrogen at −196 °C (−320.8 °F).

The freezing process results in ice crystals formed from intra- and extracellular water, and subsequent crystal growth. 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 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.

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

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.

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