If steam is generated, instead, by an external boiler it is introduced into the base of the vessel via an open coil, jets or similar device(s). The advantages of this type of distillation are that it is relatively rapid and capable of greater control by the operator. The vessel can be emptied and recharged quickly and with the immediate reintroduction of steam there is no unnecessary delay in the commencement of the distillation process. Oils produced by this means are more likely to be of acceptable quality than those produced using the more direct method.