Ask the expert - Answer by Dr. Jessica Wagener, Application Specialist Cell Handling at Eppendorf
For optimal survival rates animal cells should be stored below -130°C. Storing at higher temperatures negatively impacts viability of most animal cells over time. A temperature decrease of -1 to -3°C per minute is optimal for freezing most cell lines. This can be achieved by a programmable freezer unit or by a two-step freezing procedure. In the presence of cryoprotectants cells can be placed in a freezing container that is placed in an -80°C freezer overnight. In a second step, the cryotubes are transferred to a liquid nitrogen tank or a -152°C freezer. This controlled freezing procedure will result in optimal recovery of cultures.