Snap freezing is the technique in which a sample is rapidly frozen using dry ice, a dry ice/ethanol slurry or liquid nitrogen. Samples frozen in this manner include bacteria and viral stocks, cell lysates, proteins, and tissues. Snap freezing reduces the chance of water present in the sample forming ice crystals during the freezing process, and better maintains the integrity of the sample. In the case of tissue or lysates, snap freezing slows the actions of proteases and nucleases to inhibit degradation of molecules such as RNA or proteins.
Snap-freezing is a commonly used technique in both the food industry and for biological sample preservation because it preserves moisture content and structural integrity.
https://en.wikipedia.org/wiki/Snap_freezing