Definition: Freezing straws

Explanation: A semen sample, is mixed with a cryoprotectant (similar to antifreeze in a car) and drawn into thin plastic freezing straws. Normally between 5 and 20 straws may be prepared from each single ejaculate. The straws are coloured and a coloured plug is used to seal the end. These colour combinations are unique for each man. The man’s file number and sample number is also recorded on each straw. These straws are then placed into a programmable freezing machine and liquid is pumped into it at a controlled rate. This allows the sperm straws to be frozen in a scientifically controlled manner.