Essential oils
Practical Action
burning of the charge. The quality of the oils produced in such traditional stills can be improved
if they are heated by steam generated in a separate boiler. This, however, requires more
expenditure in capital equipment. Water distillation remains the recommended method for
barks, such as cinnamon and sandlewood, and certain flowers.
Water-steam distillation is an improvement Baffle
of simple water distillation. The charge
of plant material is supported on a mesh Still head
or grill above boiling water as shown in
clamps
Figure 2. The water is boiled, either over
a fire or by steam from a boiler using a
steam coil or jacket. This system greatly
reduces local overheating and burning of the
charge. It is important that the charge is
packed evenly and not too tightly into the
still. Over-packing will result in back-pressure
and the steam finding channels through the
charge leaving zones that have not been
extracted.
Vapour to
condenser
Plant
material
Support
grid
Water
Steam distillation is the most advanced
method and depends on live steam being
supplied from an external boiler. The
charge is again supported on a mesh above the
base of the still and above a steam coil as
shown in Figure 3.
Heat
Drain valve
The principle advantage of this method is that
“dry steam” is used which results in reduced
distillation times and hence greater outputs.
All still bodies should be insulated to reduce heat
losses and fuel consumption. In some cases they
are mounted on frames that allow them to be
inverted in order to rapidly remove the hot charge
after distillation. This reduces “turn round times”
and increases daily outputs.
Modern still bodies are usually made from
stainless steel while traditional systems use mild
steel. For the reasons described below, in many
cases, the use of expensive stainless steel is not necessary.
Open steam
ring
delivering
dry steam
Condensers
Steam containing the essential oil vapour leaves the still via a head, known as a gooseneck, and
passes to a condenser as shown in Figure 4. Simple condensers consist of a metal coil in a tank
of flowing cold water. Ideally the coil of the condenser should be constructed from an inert
material such as stainless steel in order to prevent the oil chemically reacting with mild steel. In
many traditional stills the gooseneck and condenser coil were constructed from copper or brass
that had been internally tinned to provide a reasonably inert surface. It is very important that the
condensed steam (water) leaving the condenser is thoroughly cooled. If it is still warm there will
be a loss of essential oil.
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