The most common method for essential oil extraction is steam distillation. This is a process whereby steam and cold water is used to help separate the essential oil from its host. Steam is passed through a dome-like vessel - sometimes known as a 'still' - containing plant material. The aromatic molecules of the plant are then released as vapours that rise along with the steam to the top of the vessel. These vapours then travel into a cooling chamber that is surrounded by cold water - also known as a condenser. The rapid change of temperature forces the vapours and steam to turn back into liquid form.