What is the concentration of glycerol used for storage of bacteria?

The point of the glycerol used for storage of bacteria is preventing freezing damage, such as ice crystal formation. At lower glycerol concentrations like 10-20% the frozen stock will be fairly solid at -80C, while at higher concentrations (30-50%) it may remain partially liquid. Either is fine but over time (years) the cells will settle down at bottom if still liquid. So, anything over 10% should be ok. Normally, 20%, 25%, 40%, 50% are often used.

Souce: NovoPro    2018-02-07