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.