In physics and chemistry, flash freezing is the process whereby objects are frozen in just a few hours by subjecting them to cryogenic temperatures, or through direct contact with liquid nitrogen at −196 °C (−320.8 °F).
Flash freezing is commonly used in the food industry to quickly freeze perishable food items. In this case, food items are subjected to temperatures well below water’s melting/freezing point. Thus, smaller ice crystals are formed, causing less damage to cell membranes.
Flash freezing techniques are also used to freeze biological samples quickly so 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.