The process of semen cryopreservation consists of suspending sperm in a mixture that dehydrates the cell enough not to form ice crystals that would cause lysis (cell rupture) while the cell is freezing. Semen is cooled at a designated rate. Once frozen, the semen is stored in liquid nitrogen at -196°C until it is needed.

No one really knows how long semen can stay viable but some animals’ semen has been used successfully 50 years after the initial freezing.