freeze drying (lyophilization) The removal of liquid from heat-sensitive materials. The material is frozen, placed under a high vacuum, and maintained at a low temperature (–40°C or below). The pressure generated by the vacuum causes the ice to turn from a solid to a gaseous form without passing through a liquid state. This allows the removal of water from the material without otherwise disturbing its composition. Freeze drying is used to preserve tissues (e.g. blood plasma) and foods and to concentrate solutions.

freeze drying Also known as lyophilization. A method of drying in which the material is frozen and subjected to high vacuum. The ice sublimes off as water vapour without melting.

Freeze‐dried food is very porous, since it occupies the same volume as the original and so rehydrates rapidly. There is less loss of flavour and texture than with most other methods of drying. Controlled heat may be applied to the process without melting the frozen material; this is accelerated freeze drying.