The target for humidifying the air in the incubator is to stop evaporation of culture liquid or reduce evaporation. To reach this target, in many cases it is not necessary to select the maximum setpoint of 85% rH. If a humidification is required and at which setpoint depends on the following factors:
 

• Type and size of the culture vessel
• Filling volume
• Temperature
• Duration of the cultivation
• Acceptable evaporation loss

General rules when using flasks:

• For cultivaton in large Erlenmeyer- and Fernbachflasks (2 – 5 L total volume), a humidification is usually not required.
• For cultivations in small Erlenmeyerflasks 75% rH is fully sufficient to stop evaporation. As an example: the evaporation rate from 125 mL Corning cell culture flasks with 15 mL filling volume is only 1% in 24 H (measured at 37°C/75% rH/100 min^-1).

General rules when using microtitre plates:

• For bacterial cultivations in deep well plates with 2 mL filling volume per well (typically E. coli over night at 37°C), a humidification is not required.
• For bacterial cultivation in 96well plates with 150 µL of filling volume per well, the combination of humidification with setpoint as high as possible together with the box for microtitre plates is recommended.
• For cell culture in 6well plates, a humidification with setpoint as high as possible together with the box for microtitre plates is mandatory.

For details of operating the humidity option please refer to the operating manual.