Cryopreservation of yeast cultures

A method is described that allows a wide range of yeast species to be stored in liquid nitrogen while maintaining a high level of viability. Yeast cultures are sealed in commercially available polypropylene straws after having been mixed with a glycerol-based cryoprotectant. Once placed in a secondary cryotube the temperature of the sealed straws is reduced slowly to -30 degrees C in a methanol bath over a period of up to 3 h. The straws are then transferred directly to the liquid nitrogen and placed in a racking system for long-term storage.