Water
Distillation
Water Distillation’ brings the botanical material
into direct contact with water within the retort (tank,
vessel) of the still. It is employed for plant material
such as flower petals of rose and neroli so that they
can ‘float’ freely, as steam distillation
can coagulate them into unmanageable masses. When dealing
with finely powdered plant materials water distillation
is also used to create a freely moving “soup”.
This method needs to be closely monitored as it puts
the essential oil at higher risk of being ‘burnt’,
which not only disrupts it’s fragrance, but can
destroy many of the therapeutic components of your oil.
As with other forms of distillation, only the essential
oil that steam comes in direct contact with can be vaporized.
Any oil held within the plant tissue must first be extracted
from the glands and brought to the surface of the plant
by hydrodiffusion. But these forces of hydrodiffusion
work very slowly and this can cause long distillation
times. The plant material must be properly prepared
prior to entering the retort and then enough water added
to fully cover the entire charge. It is important to
leave ample vapor space above the charge to avoid boiling
over and carrying over of spray into the condenser.
Once the charge has reached its boiling point, either
through direct firing of the retort or through indirect
steam, the condenser will start to produce distillate,
which will run directly into a separator to separate
the essential oil from the hydrosol, or hydrolat. (the
distillation water)
Many water distillation systems incorporate cohobation,
which is the return of this distillation water back
to the retort. This is advisable to prevent the plant
material from becoming exposed to the full heat of distillation
from the water level lowering below the plant material
as it evaporates. Cohobation can prevent this and thus
reduce the chances of the plant material becoming above
the water line and lumping together, becoming impenetrable
for steam, therefore not yielding its oil completely.
Cohobation also reduces the chances of the charge becoming
burnt.
Distillation times must be adjusted to the particular
material being distilled, as well as to the particular
still being used. The goal being to maintain the maximum
production of oil, representing a complete essential
oil of the botanic distilled. With some plant material
such as Vetiver root, distillation times can reach as
high as 24 hour or even greater, with older, less efficient
stills. Even with these long distillation times, one
of the disadvantages of water distillation is that the
plant material cannot always be completely exhausted.
This is due in part to the partial hydrolyzation of
“somewhat” water-soluble oil constituents.
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