A rotary evaporator (or rotovap) is a piece of distilling equipment which, like a pot or column still, exploits the different boiling points of ethanol and water to separate the two during a distillation process. However, there is a crucial difference: pressure.
A rotary evaporation system includes a vacuum pump, which lowers the pressure within the system. The lower pressure at which the distillation takes place means the ethanol and water inside will evaporate at a lower temperature. Distilling at a lower temperature means it is possible to extract more delicate congeners (flavours compounds) from botanicals that it may not be possible to extract during a traditional pot still or column still distillation (for example, from more delicate fruit or floral botanicals). A pioneer of this ‘vacuum distillation’ process using a rotovap was Sacred Spirits, founded in London in 2008.
In the general rotary evaporator set-up, the liquid to be distilled is placed in a round-bottomed flask, which is placed into a bath (normally filled with water) to ensure even heating. Throughout the distillation, this flask is rotated (hence ‘rotary evaporation’) to spread the liquid evenly around the sides of the flask. In the distillation of alcohol, the ethanol in the liquid in the flask volatises (evaporates) and is channeled into a condenser, wheere it condenses back into a liquid before being captured in a receiver.