Whoever wants to stop biological processes, must freeze. The longer the chilled
product needs to be stored, the lower should be the choice of temperature.
In the case of storage times lasting a number of weeks or months, deep freezers
are sufficient. Storage temperatures down to -80 °C are generated with cold
aggregates. If long-term storage is necessary, liquid nitrogen is selected as
the method of cryopreservation.
While freezing life samples, the cell water passes through crystalline transformations. By doing so the growing ice crystals are able to damage the cell and cause a loss of vitality. Out of this reason the freezing procedure has to be done with equipment, which is able getting the cells alive while freezing them using a cell compatible gradient of temperature. If the temperature comes up to -130 °C the glass point is reached. The crystal structure of the cell water is transformed into a high viscously, amorphously fluid. The biological clock of the cell stops. But it is ingenious to choose a storage temperature which is a little bit lower to avoid crossing the glass point temperature while taking samples with forced heating.