A process used for preserving biological material, by removing the water from the sample, which involves first freezing the sample and then drying it, under a vacuum, at very low temperatures.
Lyophilization, or freeze drying of bacterial cultures stabilizes them for long-term storage while minimizing the damage that may be caused by strictly drying the sample. Many microorganisms survive well when freeze-dried and can be easily rehydrated and grown in culture media, after prolonged periods of time in storage.
Lyophilization is also used in the biotechnology and biomedical industries to preserve vaccines, blood samples, purified proteins, and other biological material.
The process of lyophilization is actually an application of a physical phenomenon called sublimation: The transition of a substance from solid to a gaseous state, without first passing through the liquid phase. During lyophilization, the water in the frozen sample is removed as water vapor, without first thawing the sample.