Medicinal and Aromatic Plants—Industrial Profiles

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cohobation is more difficult. It is necessary to take the distillate water to a tank where it can
be adjusted for pH and possibly have boiler water treatment compounds added before being
reintroduced to the boiler.
It is worth noting that extraction of oil from various Melaleuca species is not difficult. It
is, in fact, a very simple operation.
In order to extract the oil we need to pack the plant material into a container, pass steam
through the container, collect the steam and oil vapour that distils off, condense the vapours
to water and oil, and separate the oil from the water.
Tea tree oil is a very amenable oil to distil. It comes from the leaf readily. It is not
adversely affected by the water with which it is distilled, or by atmospheric oxygen in the
brief periods between removing it from the receiver and packing in an air tight container.
Therefore no special equipment or action is required to preserve the oil at, or soon after
distillation. Separation of the oil and water is easily effected by using the immiscibility and
difference in density and of the two liquids of the distillate. The amount of oil dissolved in
the distillate water is small (negligible, if cohobation is used) and therefore recovery of oil
dissolved in the water unnecessary.
Until recently, tea tree oil was produced from natural stands and small, sometimes
movable, apparatus was required. In recent years plantations have supplied most of the oil
where larger, static and more sophisticated apparatus is used. In small plantations, and even
in the early stages of larger plantations, the small, low capital cost equipment is appropriate
and effective. A description of suitable equipment for both applications follows.
Plant Material
To obtain oil by steam distillation it is necessary to pass steam through the oil-bearing parts
of the plant. In the case of tea tree oil this means the leaves and terminal branchlets. The
main woody part of the plant does not contain oil. As the Melaleucas coppice well after
being cut, (except for the initial harvest) it is the coppice regrowth that is collected.
Consequently, the proportion of non oil-bearing material harvested is low and the whole of
the coppice regrowth can be put into the still. Where the trees are harvested by hand, some
stripping of the leaves from the larger woody stems is feasible, resulting in a higher proportion
of oil-bearing material in the still. However, for mechanical harvesting it is uneconomical
to separate the non oil-bearing part of the plant. Furthermore, there is nothing distilled out
of the woody part that is detrimental to the oil. The wood simply occupies space in the still.
For steam distillation of tea tree very simple apparatus can be effective. At present tea tree
oil is at a price where use of petroleum oil or gas for raising steam is economically feasible.
If the scale of operation is large, a steam boiler or steam generator can be used, as these
devices are efficient steam producers and can be automated. If the operation is small, the
high capital cost of establishing special steam raising equipment cannot be justified. Therefore
raising steam within the still is just as effective and more economical for the small operator,
particularly if wood or extracted leaf is the fuel used.
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

For a simple but effective direct fired still (
Plate 16
) the equipment consists of:
The firebox or boiler.
The still.
The condenser.
The receiver or separator.
The constant level tank.
Fire Box
The fire box is required if a boiler is not used and steam is generated in the still. It can be
made of metal, brick/concrete or, in some cases, earth. Its functions are to provide a base for
the still and to contain the fire. The dimensions will depend on the size of the still and the
fuel used. In all cases the box should allow the maximum area of the base of the still to be
exposed to heat from the fire, but ensure that no part of the base of the still that does not
have water above it is exposed to direct heat of the fire.
For tea tree, the cheapest fuel is dried leaf after the oil has been extracted. This requires
a fire box about 1 metre high. While the fuel is cheap and available, the necessity for constant
stoking makes use of this fuel unattractive in most circumstances. For wood fuel the box
needs to be about 500mm high, while for an oil burner 300mm is sufficient. The “box”,
which has neither top nor bottom, requires one side to be open to allow stoking of solid fuel,
or to have an aperture to take an oil or gas burner. At the opposite end an aperture to take a
flue is necessary. In the case of using an oil burner a baffle is required to distribute the flame
from the burner so that it impinges on the base of the still instead of going directly up the
The flue of at least 150mm diameter needs to be carried horizontally 3 or 4 metres from
the still to reduce smoke and heat near the still and then vertically about the height of the
still to cause a draught, or a straight flue can be set at an angle to achieve the same effect. A
tall flue, while more effective in getting smoke away from the still, causes too much draught,
so dragging too much heat from the fire box. It is possible in some sites to set up a still by
excavating a fire-box in the earth and having no made-up fire-box at all. However a flue is
essential for comfortable operation of the equipment.
The Still
There has been a great deal of argument about shape and size of stills. My experience is that
shape is of very little consequence. The essential factors in building an effective still are that
steam passes uniformly through an evenly packed charge of leaf and can flow smoothly
from the still without much pressure developing in the still.
It is worth noting that the simplest of stills, consisting of no more than a 200 litre standard
drum, direct fired, and with a 50mm galvanised iron pipe as a condenser running down
through a creek or pond can produce an oil equivalent in both quantity and quality to an oil
extracted with the most sophisticated equipment.
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

Therefore in designing a still the main consideration is ease of handling the plant material
and economy of operation. The size of the still needs to be related to the amount of leaf to
be processed. It is obviously uneconomical to establish a still with a capacity to handle
much less leaf than is available. It is also undesirable to have a still which cannot be filled
completely before commencing distillation. The yield of oil per unit weight of leaf tends to
be lower in a partially filled still. Although tea tree leaf can be left for some time after
harvest, some deterioration, particularly in hot humid weather, is likely if harvested leaf is
kept too long before being distilled. In a properly charged still, a cubic metre of still space
will take 250–300kg of chopped plant material. If the still is to be moved from time to time,
the size needs to be related to the equipment available for dismantling, transporting and
setting up again.
Other factors to be considered in still design are:
1. The still can be made of mild steel or stainless steel. The former is cheaper and therefore
suitable for bush stills and small scale plantations. Stainless steel stills, while more
expensive to establish, last longer. The quality of the oil produced in mild steel stills
is in no way inferior to oil produced in stainless stills.
2. There must be no obstructions to the loading and unloading of leaf, i.e. whether box-
shaped or cylindrical, the top must open fully.
3. Steam distribution must be adequate. This can be achieved by means of tubes on the
floor distributing steam evenly under the charge where steam is injected, or by placing
the leaf on a mesh or perforated plate above the water in a direct fired still where
steam is generated in the still. This method can also be used for injected steam. In all
cases even and firm packing of the leaf is necessary.
4. The steam and oil vapour outlet must be near the top of the still and be large
enough to facilitate rapid passage to the condenser, thus preventing pressure
building in the still.
5. A drain, at least 50mm diameter should be placed at floor level to facilitate cleaning
the still, and in the case of the steam-injected still, to allow drainage of excess water.
6. A water inlet, usually a 50mm socket, is best welded in the wall about 50mm from the
floor to allow for “make up” water during distillation or water from the receiver in the
case of cohobation.
7. The mesh or perforated tray on which the leaf is stacked needs to be loose enough to
be easily removed to allow cleaning the floor of the still. Where steam is injected,
provision for cleaning the distribution tubes must be made, e.g. removable caps on
the end of the tubes, or open ends where small diameter tubes are used.
8. The base of the still should extend beyond the walls by about 200mm if the still is
sitting on bricks so that almost the whole of the base is available to transfer heat from
the fire to the water above, but the fire must not impinge on any part of the base that
does not have water above it.
9. Adequate provision must be made for sealing the lid when closed.
10. The lid should be insulated, particularly if the still is in the open. Insulation of the
walls is not so important.
Typical stills giving layout and dimensions are shown in 
Figures 1
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

The Condenser
The function of the condenser is to convert the steam and oil vapour that issues from the
still to water and liquid oil at the desired temperature. The commonest types use water as
the coolant although air-cooled condensers can be used in some circumstances, as can
If flowing water is available, very little equipment is required to construct an effective
condenser. For field stills, or small plantation stills, metal pipes running from the still
to and under a stream or pond are quite effective. The above-water section of the pipe
should be short if possible, or if it has to be long, should be at least 75mm diameter for
Figure 1 Layout of a simple still for the production of tea tree oil (Designed by G.R.Davis Pty Ltd for,
and reproduced with, the permission of CSIRO Forestry and Forest Products)
Figure 2 Plan view of the above tea tree still
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

a still of 3m
 or more capacity. Once under water a 50mm diameter tube is sufficient.
This needs to be at least 20m long. With this system the fall in the stream has to be
sufficient to allow the construction of a dam through which the condenser pipe runs so
that the outlet is above water. As the condenser pipe must run downwards throughout
its length, the receiver into which the condensate flows must be below the water level
of the stream or pond.
This type of condenser, which is very simple and cheap is widely used in hilly country,
but is not suitable for flat or swampy country. For flat country a condenser can be set up
close to the still, and consist of a tank containing a volume of water with a pipe running
through it, usually as a descending spiral. In this type the cooling water is static, requiring
no pump. If the volume of water is sufficient, after cooling overnight or between
distillations, it will cope with the next distillation. Occasional topping-up to replace water
evaporated from the tank is all that is required. This is an effective type of condenser,
easily made and cheap. About 20m of tube beneath the water is sufficient; say 3 lengths
of galvanised 50mm tube.
A more compact and more portable condenser is the multitube type in which the hot
distillate flows through a number of tubes while the coolant is pumped in a jacket around
the tubes. In some cases the vapours flow in the space around the tubes while the coolant
flows through the tubes. The advantages of this type of condenser are that it is much more
compact, easily established and transported, easily cleaned and, because the hot vapours
contact a large area of cold surface immediately on entering the condenser and collapse to
liquid at that point, the resulting diminution in volume tends to pull the vapour from the still
to the condenser.
The tubes, through which or around which the vapours flow are nowadays usually stainless
steel. Other metals can be used provided they have reasonable conductivity and do not react
with the oil.
The disadvantage of multi-tube condensers are the high cost and the necessity for
a pump and motor to push the coolant through the condenser, unless it is possible to
gravitate the water from a stream as is often done in hilly country. Where electric
power is available, the necessity to pump is not much of a disadvantage, although it is
a cost since the pump must run continuously during the distillation. Where no electric
power is available from the grid, small petrol motors are the usual source of power.
These are not always reliable and therefore the static tank type condenser is more
The capacity of the condenser has to be considered in relation to size of still and speed of
distillation. With the static tank type it is not much more expensive to set up a 10,000 litre
tank than a 5,000 litre. The cooling coil is the same. With the extra volume of water, the
only time the condenser can be inadequate is when several distillations are done in rapid
succession in hot weather. Even then, all that is necessary to get effective condensation is to
push some cold water into the tank, displacing the hot water.
With a multi-tube condenser, if it is vapour-in-tube type, it may be mounted vertically or
at any angle down to almost horizontal. There must always be enough slope to enable the
condensed vapour to flow to the outlet. If the condenser is coolant-in-tube type, it is best
mounted vertically. Unless it is very well designed a horizontally installed condenser of this
type is likely to condense but not cool the distillate.
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

The effectiveness of a condenser depends upon the surface area available for heat transfer,
the heat conductivity of the metal cooling surface, the difference in temperature of the
distillate and the coolant, and the rate of vapour flow into the condenser. The third factor
can be controlled to some extent by the rate at which the coolant (water) is pumped through
or around the tubes. The first two factors are fixed for any condenser. It is therefore essential
to make sure that the condenser is big enough before installation. If it is not, the rate of
distillation will be limited.
Receiver or Separator
For tea tree the liquid oil and water flowing from the condenser during distillation are, for
practical purposes, non-miscible and of different densities. Therefore separation can be
achieved by allowing the oil to rise to the top of the mixture. There are essential oils with a
higher density than water, and some with a density close to that of water. These require
different apparatus or treatment, but for tea tree oil simple flotation is an effective means of
separating oil and water.
The essential features of this type of separator are that it must be able to collect the
distillate flow as it comes and be of sufficient volume to allow the liquids to settle so that
there is no current flowing through. This can be done by introducing a second vessel within
the main one, but if the volume of the primary vessel is large enough effective separation
will occur. If cohobation is employed, any oil not separated will return to the still and come
over later in the distillation.
An effective separator can be made by using a drum, e.g. 200 litre, into which the
distillate flows, with an outlet for water from close to the bottom taken up to 3/4 of the
height of the drum, and another outlet for the oil directly through the wall at the same
Figure 1
 illustrates this. For a lighter-than-water oil such as tea tree, introducing
the distillate through a funnel with a turned up end has some merit as this directs the flow
of oil globules upward.
If the condenser is of stainless steel, a separator of the same material tends to keep the
oil free from colour, although stainless steel is not essential for either apparatus. Where
the densities of the two liquids of the distillate are close, the temperature of the distillate
is important, as, for oils lighter than water, difference in densities will increase as the
temperature rises. However, for tea tree oil the difference at ambient temperature is
sufficient for effective separation. There is no advantage in operating at other than ambient
Constant Level Tank
A constant-level tank in association with the still is desirable with a direct-fired still. This
can be a 60 litre or so drum, with its base set no higher than the base of the still. From this
drum about 50mm from the bottom, a pipe, say 50mm diameter, runs horizontally into
the still. Thus, provided there is at least 50mm depth of water, the water level in this drum
and in the still will be the same. As distillation proceeds, the water level in the still tends
to fall as steam is evaporated off. Water from the drum runs in to replace the evaporated
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

water. This replacement water comes from the separator into which the condensed distillate
flows. Although it is not necessary or in fact desirable to have much water in the still at
the beginning of the distillation, it is essential that there is enough to ensure that the
bottom of the still is covered at all times. At least 60mm of water should remain in the still
after water is evaporated up into the charge of leaf and before the vapours have condensed
and run into the receiver, from which water will then flow to the constant level tank, and
then back to the still. To guard against the water level falling too far before the distillate
starts to flow, a pipe from the condenser tank, or the condenser water line where a multi-
tube condenser is used, runs to the constant level tank where water enters through a float
valve. Therefore, when the water level in the still falls to a pre-determined level coolant
water from the condenser enters the constant level tank and flows through to the still.
This safety device also comes into play if the distillate is not condensed for any reason, or
if the still springs a leak.
In putting the apparatus together it is essential to have the various components at the right
levels. The vapour outlet duct may rise if necessary. If so, it is necessary to insulate the duct
from the still to the condenser. If vapour condenses in an upward-sloping duct it will run
back into the still and have to be re-vaporised. Because of the size of the drops running
back, much more time is required to vaporise the oil the second time. The vapour duct
needs to slope up only where the height of the condenser is greater than the vertical distance
between the vapour outlet and the water return inlet to the still. There must be sufficient
height to allow the distillate to flow from the condenser to the receiver and then to the
constant level tank. See 
Figures 1
When the apparatus is assembled, water is added to the still (if steam is to be generated
in the still) to a level of approximately 100mm. The leaf is carried on a mesh about 150mm
from the floor, i.e. 50mm above water level. Water is also added to the condenser tank, or in
the case of a multi-tube condenser, the pump that pushes water through the condenser is
started. The receiver/separator is filled with water until it just overflows into the constant
level tank which in turn overflows into the still to which it is connected. The still is packed
with leaf, the lid of the still is closed and sealed and the fire is started or steam from a boiler
Packing the leaf into the still must be done with care. With machine harvesting the leaf
material normally packs evenly, although some positioning of the chute of the harvesting
machine might be necessary to achieve this. In the case of hand packing of the leaf, care
must be taken to ensure there are no sections of loosely packed leaf through which most of
the steam will travel. If there are loosely packed sections distillation will be prolonged, or
possibly not completed.
The initial task in distilling is to raise the temperature of the leaf to a point where the
oil and water vaporise and flow to the condenser. Therefore it is desirable to push the
steam through the leaf mass rapidly in the early part of the distillation. The more steam
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

that is pushed into the leaf, the more rapidly will the temperature rise to distilling
temperature, i.e. just below 100°C. At this stage the condenser has not come into operation
and there will be a slight increase in pressure in the still. As the distillate starts to flow,
one must consider the capacity of the vapour duct and the condenser to handle the flow. If
the vapour duct is large in diameter and short, and the condenser the type in which the
vapours meet a large cooling area immediately on entering, e.g. multi-tube type, a vigorous
rate of distillation can be maintained. If the vapour outlet from the still is restricted or the
condenser is of the long, small diameter, single-tube type, where condensation occurs a
long way down the condenser, the distillation rate, i.e. the amount of steam being generated
in the still, or being injected from a boiler, will have to be reduced to avoid building
pressure in the still or pushing the vapours through without complete condensation, thus
losing oil to the atmosphere. Once condensation occurs, the collapse of vapours to liquid
which occupy a very much lower volume, causes vapour to be pulled from the still, so
reducing pressure in the still.
A steady distillation rate is desirable. If the rate slows too much, oil vapour will
condense on the lid or the walls and fall back into the leaf, from which it has to be
vaporised again.
The end of the distillation can be determined by collecting, in a narrow cylinder or
bottle, a sample of the distillate as it flows from the condenser and visibly assessing the
proportion of oil to water. Where fuel is not expensive, allowing the process to continue
results in maximum yield of oil, and with tea tree, no serious decline in quality of the oil.
Where fuel is costly, a point is reached where oil recovered in the late stages of the
distillation is insufficient to cover the cost of the fuel for this stage. Demand for the still
must also be considered. If distillation is not keeping up with harvesting, starting a new
batch might be preferable to continuing the old distillation in order to gain a very small
quantity of oil.
The time required to distil oil from plant material depends on a number of factors. In
particular, the physical structure of the oil-bearing part of the plant, the chemical
composition of the oil, the design of the distilling equipment and the packing of the
still. For any oil, the first two factors are constant. The time required for distillation
therefore is determined mainly by the amount of steam put through, which in turn
depends on the design of the still, the capacity of the condenser, and the packing of the
Leaf should be removed from the still within a few hours after distillation is complete.
If the charge is left in the still for several days or more, removal is more difficult, and
the life of a mild steel still is shortened due to rust when the metal is wet. The simplest
method of removal is to lay chains on the platform on which the leaf is packed (one
chain along the centre of the base and one more at right angles is usually sufficient)
carry the chains over the sides until the still is filled, then lay the ends of the chains on
top of the leaf. A lifting device is then used to pull out the leaf mass. In a still, other
than a very small one, it is necessary to pull the leaf out in two or more layers, as the
weight of the compacted wet distilled leaf plus the friction to be overcome calls for
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,

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