Freeze

Freeze is the process by which a substance changes from a liquid to a solid as heat is removed. The temperature at which this occurs is called the freezing point; it depends on the substance and on pressure and impurities. For water, the freezing point is 0°C at standard pressure. Freezing is a phase transition that releases latent heat of fusion. In common usage, "freezer" refers to a refrigerator compartment kept at low temperature to preserve items.

Ice formation begins with nucleation, where small ice crystals form, followed by growth as molecules arrange into a crystalline lattice. The rate of cooling and presence of impurities influence crystal size and texture. Supercooling can occur when a liquid remains liquid below its freezing point in the absence of nucleation, and a disturbance can trigger rapid solidification.

Freezing is widely used for food preservation, slowing microbial growth and enzymatic reactions. Home freezers typically operate around −18°C to maintain quality. Freeze-drying is a related technology that removes water by sublimation after freezing. Cryopreservation uses controlled freezing of biological samples with cryoprotectants to limit ice damage.

Biological adaptations include organisms that tolerate freezing by producing antifreeze proteins, sugars, or other solutes that lower the risk of intracellular ice formation. Others avoid freezing by remaining in a supercooled or desiccated state.

In computing and media: In computing, to freeze a program means to halt activity, preventing input or changes. In film and video, a freeze-frame is a still image captured from a moving sequence.