The procedure for slow freezing typically involves several steps. First, the tissue is placed in a cryoprotectant solution to protect it from ice damage. Then, the temperature is gradually reduced, usually in a programmable freezing machine. The cooling rate is generally around 0.3°C to 0.5°C per minute until it reaches around -30°C to -40°C. After this, the samples are plunged into liquid nitrogen at -196°C for long-term storage.
