Steam distillation brings steam in direct contact with the plant material in the retort from an outside source. A steam boiler is generally used, producing live steam, usually of a pressure higher than atmospheric. From here the steam is injected into the retort which may operated at or about atmospheric pressure, or may also run above or below atmospheric pressure. Steam distillation is the most common of distillation methods today with most of our essential oils being produced via steam distillation. Similar care must be taken with the plant material as in steam and water distillation, however, it is also important with steam distillation to consider the wetness factor of the steam being employed. All steam is not created equal, superheated steam is considered a “dry” steam and can cause a charge to dry out while saturated steam can have the opposite effect and result in the problems associated with a steam and water distillation. It is important to monitor steam dampness and adjust to the plant material being distilled to achieve efficient and complete distillation. Overheating of the plant charge can be a result of superheated steam. As mentioned, hydrodiffusion is of major importance in distillation of essential oils. It is this process that allows essential oil to interact with water to draw the essential oil to the surface a plant material where the essential oil is found within the plant structure. If a plant material becomes overly dry, due to superheated steam, this hydrodiffusion is halted and essential oil recovery again incomplete. The ability to control the wetness factor of steam distillation is one of its major advantages over water and water and steam distillation. |
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