Oleoresins
and Resinoids
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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