text: After the sample has been processed for cryoprotection, the sperm is stored in small vials or straws holding between 0.4 and 1.0 ml of sperm and then cryogenically preserved in liquid nitrogen tanks. Two approaches for sperm cryoperservation include conventional freezing and vitrification. The conventional technique consists of a slow freezing process that is most commonly used for assisted reproduction technologies (ART). Whereas the vitrification method is a faster approach for sperm cryopreservation in converting liquid to solid state. The disadvantage of this latter process is increase in contamination from the liquid nitrogen and smaller sperm sample size to improve the speed for high cooling rate.
  It has been proposed that there should be an upper limit on how long frozen sperm can be stored; however, a baby has been conceived in the United Kingdom using sperm frozen for 21 years and andrology experts believe sperm can be frozen indefinitely. The UK government places an upper limit for storage of 55 years.
  Following the necessary quarantine period, which is usually six months, a sample will be thawed. To thaw a sperm sample, the vial or straw is left at room temperature for approximately 30 minutes, and then brought to body temperature by holding it in the hands of the person performing the insemination. Once a sperm sample is thawed, it cannot be frozen again, and should be used to artificially inseminate a recipient or used for another assisted reproduction technologies (ART) treatment immediately.
  Freeze-drying is another promising alternative for storing semen for its accessibility with regular refrigerator. This method has been successfully replicated in animal species. However, DNA can be damaged in this process, therefore further research is warranted to determine factors that can effect the efficacy of this method.