The Distillation of Essential Oils Part 2 in Personal Care magazine July 2012

1. Murray Hunter – University Malaysia Perlis ESSENTIAL OILS
The distillation of
essential oils 2: PART
Part two of this three part series on distillation carries on from the basic principles laid out in part one to look
at the stages of the general distillation process and outlines the various basic types of distillation.
Distillation occurs in a number of definable Stage one Stage two Stage three
stages. During the first stage, initial heating
occurs through the charge where the plant
material has been placed. Plant material Linalool
will not be saturated with moisture and the
temperature differential between the steam
Percentage increase of the distillate
and the plant material will allow quick
Methyl chavicol
dissipation of latent heat from the steam to
the plant material. The initial steam,
particularly if it is wet will tend to cool
throughout the lower layers of the charge,
where some condensation may occur. This
has to be watched carefully, as too much
1,8 Cineole
condensation may flood the lower parts of
the charge. Dry superheated steam may
have the effect of drying out the plant
material. Both flooding and drying out of
the plant material are detrimental to
efficient distillation. At this early stage
steam is the only contributor to vapour Eugenol
pressure until saturation occurs and the
layering process, discussed above begins.
The second stage begins when the Progressive number of constituents
vapour reaches the condenser. At this point
the oil-to-water ratio will be at its highest. Figure 1: The distinct stages of distillation, and during the second phase, for sweet basil oil.
During the second phase the distillation
process will go through three sub-phases. the change in composition of sweet basil the vat and the plant material surfaces
ɀ In the early stage, due to some effect oil during distillation.2 area within the charge. The rate of steam
from relative volatilities of the various The height of the still will influence this flow per hour is subject to the amount of
constituents, the most volatile phenomenon. High stills tend to negate plant material in each charge. Daily
constituents will tend to vaporise first this effect because as the more volatile throughput is thus limited by the amount of
and carry a higher than proportionate constituents from the bottom layer reach steam that can be generated on an hourly
weight in the distillate as compared to the top layer, the less volatile constituents basis at a distillation plant. Steam must
the normal oil. It is also reported that from the bottom layer will have already also be adjusted to suit the absorptive
oxygenated constituents also have a started distilling over and reaching the capacity of the plant material. This greatly
tendency to distil over before upper layers of the charge. varies between different herbs and the
hydrocarbons.1 The final stage of distillation occurs condition they are in before distillation.
ɀ During the middle stages, the oil will be when the water-to-oil ratio is very high as Steam produced by high pressure
distil over in the same proportions as the charge becomes exhausted of oil. It will external boilers is usually very dry and can
the normal oil, and no longer be economical to continue with often be superheated. Steam produced by
ɀ During the third stage, the least volatile the distillation. medium pressure boilers around 3
constituents of the oil will contribute a atmospheres pressure will contain
higher than proportionate composition in Steam and pressure moderate moisture content, but will not
the distillate. For efficient distillation, i.e., achieving the tend to superheat. Steam produced from
maximum amount of oil with the minimum evaporators at atmospheric pressure is
The distinct stages of the second stage quantity of steam, requires the maximum relatively moist. In water-steam distillation
distillation can be seen in Figure 1 showing exposure between the steam flowing into array where steam is produced in the same
July 2012 P E R S O N A L C A R E 67

2. ESSENTIAL OILS
vessel that the plant material is stored will that the temperature gradient increases, Recently a variation on the operation of
produce very wet steam. thus increasing the effects of latent heat pressure in steam distillation has been
Different steams can be utilised as a exchange and reduces the likelihood of reported a number of times, utilising a
control mechanism to correct the hydrolysis. However the use of high technique called instantaneous controlled
conditions within the still housing the plant pressure distillation is limited by the extent pressure drop (DIC). This is a technique
charge. that prolonged high temperatures will where the foliage is first exposed to
Wet steam is a saturated vapour is damage the composition of the essential saturated steam and then the pressure
suitable for most distillation. In most cases, oil. drastically dropped to a vacuum level of
wet steam from a water bath produces ‘a Inversely, as operating pressure is around 5-50 KPa to provoke auto-
richer oil’ with much shorter extraction time reduced, so does the temperature of the vaporisation of the superheated volatile
than other forms of steam.3 This is distillation. This method can be used for compounds through expanding and
particularly the case with plant material the extraction of heat sensitive constituents breaking up the cell walls with
that contains superficial oil glands. that would normally be damaged through instantaneous cooling.4 Experiments have
Increasing steam rates does not speed up exposure to excess heat. However shown that results can be varied through
distillation, especially if the process of distillation under reduced pressure has a changing time, pressures and the amount
hydro-diffusion is required. As plant number of limitations. Steam under of moisture in the leaves.5
material is already saturated with moisture reduced pressure is less dense, so requires
and there is a constant diffusion rate. If more steam to carry out a distillation than Wilting crops before
herbs contain a lot of moisture, then there under normal atmospheric pressure. The distillation
would be sufficient moisture in the plant condenser system would need to be As the moisture condition of the herb is a
material to commence hydro-diffusion and almost twice the size of a conventional still factor in the efficient distillation of the
dry steam would be the most suitable to or a refrigeration system required in herb, wilting is often carried out to dry the
apply. However dry steam has less mass condensing the distillate. The recovery crop before processing. The objective of
than wet steam and as such reduces the vessel and separator would have to be wilting is to dry the herb enough to
latent heat of steam, thus prolonging the sealed within the closed system, which increase its absorptive surface. Many
distillation period. would lead to design and engineering practitioners believe it is to dry out excess
A superheated steam occurs when the difficulties. moisture so that distillation will be shorter
temperature of the vapour is higher than
that of the same saturated vapour at the
same pressure. Superheated steam is
independent of pressure and therefore
advantageous in a number of situations, as
it can be utilised at any temperature
without increasing pressure, i.e., can
increase the temperature of distillation
without having to change the steam flow-
rate due to changes in pressure.
Superheated steam can be used for drying
out a flooded charge vessel, where there is
too much liquid around the plant material.
However superheated steam is not
advisable for general distillation as it would
dry out the plant material, preventing the
hydro-diffusion process occurring and is a
poor conductor of latent heat – two of the
important processes needed for efficient
distillation. Superheated steam is most
suitable for the distillation of glabrous herb
material and can increase yields
substantially.
High boiling oils exert less vapour
pressures and require relatively large
temperature gradients to extract them
during distillation. This leads to prolonged
distillation periods. If the constituents are
stable under long periods of heat,
distillation can be performed under
pressures above the atmosphere, which
increases temperature. This cuts back on
distillation time and saves energy. As
increasing the still pressure, increases
temperature, the temperature gradient will
also increase between the vapour space in
the still and the plant material. This assists
in the vaporisation of high boiling volatile Figure 2: Mint foliage, cut and laid on the ground for wilting, being picked up by the harvester
constituents. The advantage of pressure is for distillation at Myrtlefor, Victoria.
68 P E R S O N A L C A R E July 2012

3. ESSENTIAL OILS
and more efficient. However this is a
Condenser cooling
fallacy. For example, with tough leaves like
water outlet
eucalyptus and tea tree, wilting does little
to dry them out or increase their surface Vapour condenser
absorption, so wilting will have no benefit
to the distillation process. Moisture in the
Vapour outlet
plant material is actually of benefit to the to condenser
distillation process.6 In fact there are risks
with wilting in that the process may lead to Condenser cooling
Still chamber for water inlet
losses in oil, not through evaporation, but
plant material
through chemical reactions like oxidisation, (loaded by
resinisation and the formation of glycosides cartridge,
and enzymes in the materials. Excessive or directly)
drying of moisture can remove necessary
moisture breaking the contact between the Welded wire
Separator
oil component and surface of the plant Steam inlet mesh floor
flask
material, thus hindering the promotion of from boiler Steam outlet
hydro-diffusion during the distillation
process.
Which crops require wilting before Still drain valve
distillation generally depends upon their
natural surface absorption capacity. Non- Figure 3: Diagram of a steam distillation still.
absorptive herbs like mint and basil need
some wilting to promote absorption during which need to be comminuted before become part of the boiling mixture and
distillation, as wilting to promote partial distillation, like almond powder and huon resulting mixed vapour.
breakdown of the surface cellular structure pine saw dust. As water boils and converts to steam at
of the leaf. In this case distillation would In water distillation there are a number the bottom of the vat and rises through the
then commence with a wet steam fraction, of simultaneous processes that act to plant charge, it will come into contact with
followed by slightly drier steam once extract volatile constituents from plant the plant material. Some oil is exposed on
moisture has permeated into the leaf material that are different from steam the surface of this material will be
structure. Herbs with absorptive surfaces distillation. vaporised by the rising steam as it comes
like lavender do not need to be wilted. In Essential oils contain a number of into contact with the plant surfaces. This
fact they do not have enough moisture to oxygenated constituents that are relatively steam carrying some volatile vapour will
link the oil glands to the surface via a water soluble in water. This would include rise to the surface and carry over into the
interface, so wet steam fractions are phenols, alcohols and some aldehydes. vapour space above the water until it
needed during distillation. Grass crops like During the early stages of a water reaches the still condenser.
lemongrass and citronella contain enough distillation, these compounds would The boiling temperature of water at the
moisture within their leaf structure to dissolve in the surrounding water and bottom of the vat in water distillation is
create a water-oil-surface interface for
hydro-diffusion to occur during distillation, Table 1: Some common water soluble aroma chemicals in essential oil.
so wilting is not necessary. As moisture
content is already sufficient in the leaf, dry Slightly soluble Moderately soluble Very soluble
steam would be suitable for the distillation (<500 ppm) (501-1999 ppm) (>2000 ppm)
process. Aldehyde C11 Calamene Benzlaldehyde
Aldehyde C12 (lauric) 1,8-Cineole Benzyl acetate
Water distillation
Aldehyde C12 MNA Nerol Cinnamic alcohol
Water distillation involves distilling plant
material totally immersed in water. Amyl cinnamic aldehyde Neryl acetate Citronellyl acetate
Depending upon the specific gravity and Amyl salicylate Rose oxide α-Copanene
charge mass in the still, the material will Benzyl salicylate Eugenol
either float or sit totally immersed in the Cedrol Geranial
water. Heat is introduced by direct heating Citronellol Geraniol
of the sides of the vat, a steam jacket, a
Citronellyl butyrate Limonene
closed system coil or in some cases a
perforated steam coil. Water distillation was Citronellyl formate Linalool
the only method used before the 20th Eudesmol Mentone
century. Geranyl formate Myrcene
Water distillation is useful for the Limonene (E)-β-ocimene
distillation of flower materials which would Linalyl acetate Phenylethylacetate
normally congeal and form lumpy masses
α-Pinene Phenylethylalcohol
under steam distillation, where steam
would not penetrate, like rose petals and Sabinene
orange blossoms. This method is also Terpinen-4-ol
useful for fruit kernels that would form α-Terpineol
glutinous masses under steam distillation Terpinolene
and powdered forms of plant material
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4. ESSENTIAL OILS
slightly less than the boiling point of water, the plant surface material as possible material from directly coming into contact
due to the mixed liquid of solublised during the distillation. with the heating coils.
volatiles and water. Heat applied to the still The effects of hydro-diffusion are much With many materials, part of the oil
will cause the creation of a small bubble of slower in water than other types of dissolves in the water during distillation and
saturated mixed vapour from the liquid distillation. Consequently, especially for forms a milky emulsion, as a number of
phase, where upon formation it rises to the wood materials extensive comminution aromatic constituents are soluble to some
top of the water in the charge. During the must be undertaken so that particles in the degree in water. This loss could range up to
rise, the bubble’s pressure, temperature charge are fine and as much oil as possible 25% of the essential oil.7 This means that
and proportion of oil to water decreases. is exposed on the surface of the material. the recovery of oil is incomplete and the
The condensing volatiles, mostly being less In water distillation, plant material is recovered oil will be deficient in some
dense than water, float to the top of the placed in a sealed vessel or retort that constituents that would be the case with
water and form a film on the surface of the connects directly to a condenser. From the the oil recovered through steam distillation.
water in the vessel. This lost oil tends to condenser the distillate runs into a Upon separation in water distillation, the
remain on top of the surface and cannot separator. The rate of distillation is water distillate is returned directly to the
re-vaporise easily due to its higher boiling controlled by the intensity of the fire, the charge vessel to replace the decreasing
point and the generally cooler temperatures pressure of the vessel or retort and/or the water level due to evaporation. This is
at the water surface. Most of the oil rate of introduction of steam. As many called cohobation. Sometimes the water
recovered in water distillation is the portion woods contain high boiling compounds, distillate is redistilled in another vessel to
of the oil that does not condensate through pressure is vital to create high enough extract the volatiles in emulsion. Salt is
this action. temperatures to vaporise the volatile often added to the distillate to reduce the
Observation shows that distillation constituents. These constituents may take solubility of water. Whether this process is
undertaken with vigorous boiling produces many hours to boil out. Hydro-stills should undertaken depends upon the probability of
better and quicker yields than mild boiling. generally be wide to maximise the the constituents being damaged by further
Some distillers even install small propellers evaporation area. Where particles are fine heat and the economics of re-distillation.
intruding into the side of the still to assist such as saw dust and powders some form Another method to recover the dissolved
in agitation. This is most probably effective of mesh or “P” shape pipe arrangement aromatic materials from the water distillate
because the agitation in the charge tank should exist at the entrance to the is to add a solvent. The mixture is then
prevents oil droplets clinging to the herb condenser to prevent plant material from vigorously shaken to pick up dissolved
surfaces. It is necessary to generate entry and possible clogging. Heavy charges constituents from the water into the
enough steam in the water so that it will and where heat coils are used in the still solvent. These materials are then recovered
come in contact with as much of the oil on require a perforated grid to prevent plant through vacuum distillation of the solvent
Table 2: A comparison between water, water and steam and steam distillation.
Water distillation Water and steam distillation Steam distillation
Construction Usually simply constructed, Inside vat contains a grill where Utilises an outside steam source
based on ancient designs. plant material rests above the water
Plant material suitability Finely powdered materials such Can be used for most herb and Most materials, except fine
as woods and rhizomes, flowers leaf materials. Material must powders. Good for high boiling
that congeal with steam. be packed in a uniform materials. Material must be packed
Not suitable for materials that manner to avoid channeling in a uniform manner to
contain acidic material which can of steam. avoid channeling of steam.
saponify, water soluble or
high boiling constituents.
Material must be completely
covered with water.
Hydro-diffusion Excellent Good Steam should be slightly wet to
promote diffusion. Superheated or
high pressure steam can dry out the
plant material and inhibit diffusion.
Available Pressure Atmospheric pressure Atmospheric pressure Can be adjusted for both high and
reduced pressures.
Available Temperature 100˚C, but care must be taken Approximately 100˚C Can be increased or reduced
not to burn the plant material according to pressure used.
from direct heat on the sides.
Hydrolysis Condition Usually a high rate of ester Hydrolysis is usually low, however Slight hydrolysis.
hydrolysis. excessive wetting of the plant material
through prolonged distillation can
promote hydrolysis during later
stages of distillation.
Rate of distillation and yield Slow rate of distillation. Moderate distillation rate. Fast rate of distillation.
Low rates of yield due to Good yields if no channels Good yields if no channels
hydrolysis and loss of water occur in charge. Usually good yields. occur in charge. Usually good yields.
soluble constituents into the
water. High boiling constituents
often left undistilled.
70 P E R S O N A L C A R E July 2012

5. ESSENTIAL OILS
which results in a secondary essential oil.8
Some common water soluble aroma
chemicals in essential oils are listed in
Table 1.
Another method that will contribute to
minimising oil loss due to oil solubility in
water during the separation phase is to
control the outgoing distillate temperature
from the condenser. Where oils are less
dense than water, there will be an optimal
temperature range where oil particles will
freely float to the top of the distillate upon
condensation. Some literature on
distillation practices misses the point about
the effect of condensation temperatures on
oil yields.9 Based on private work,10 the
higher the temperature of the outgoing
distillate, the freer will be the oil particles
to float to the top. For example, tea tree oil
droplets will float to the top of the water
distillate twice as fast at 60°C than at
40°C. The upper temperature limit will be
restricted by the potential loss of low
boiling volatiles during condensation. This
has implications on the design of the Figure 4: The condenser, with the end manifold removed to expose the internal cooling pipes,
specific condenser for specific crops and at the author’s property in Perlis, Malaysia.
set range limits upon the temperature that
distillation can take place, to achieve a water distillation. Water and steam steam distillation facilities are designed and
specific outgoing distillate temperature distillation has another advantage over built with the correct steam ratings, they
range. steam distillation as there are fewer are much more economical to run than
decomposed products during the process water and water and steam distillation
Water and steam distillation due to less chance of plant material drying systems. A comparison between water,
Water and steam distillation involves the out. However water and steam distillation water and steam and steam distillation is
storing of the plant material above a water will take a lot longer. Water and steam shown in Table 2. below.
bath situated in the bottom of the charge distillation can produce very good results
vessel and heating the water either through under reduced pressure. The condenser system
direct fire, a steam jacket or a closed or Water and steam distillation is much A condenser in an essential oil distillation
open steam coil. Water and steam cheaper to set up than steam distillation system is a heat exchange or dissipating
distillation produces saturated wet steam at facilities and lends itself to portable stills device. The condenser must not only cool
the prevailing vessel pressure, which is that can be transported from place to the condensate vapour into a liquid, but
usually atmospheric pressure. Within this place. also cool the condensate to the
configuration, unlike water distillation, only temperature range where the oil will
steam comes in contact with the plant Steam distillation separate spontaneously from the water.
material. Steam distillation employs an external The usual array for a condenser system
Water and steam distillation is not very steam generation system, external to the is a tube or set of tubes running through a
suitable for fine materials as steam will find charge vessel. This configuration provides sealed water reservoir to cool the pipes. It
a path of least resistance tending to create much more control (depending upon the is immediately attached to the top of the
channels. This means that steam will not boiler capacity) than water and steam charge vessel to collect all vapour exiting
flow through the whole mass of plant distillation. This is because in steam the vessel. The design of the condenser
material and an incomplete distillation will distillation the wetness fraction, must ensure that the vapour flow is
take place. If the plant material is loosely temperature and pressure can be turbulent inside the tubes to prevent high
packed, the same effect will happen, as manipulated according to needs and velocity vapour freely flowing through the
the material will offer no resistance to the conditions. However, it is a misconception condenser and maximise exposure to the
steam. that greater steam volumes and increased cooler walls. A baffle is usually installed at
Water and steam distillation may take a pressures have positive effects on the the beginning of the condenser to disrupt a
long period of time to reach operating process in all cases. As mentioned straight steam flow for this purpose. Failure
temperature as the plant material needs to previously, dry and superheated steam has to achieve those conditions would result in
be heated up with only saturated steam. the effect of drying out plant material, some vapour failing to condensate. Within
This may cause early condensation and which potentially halts distillation through the condenser system the flows of vapour
wetting of the plant material. the stopping of hydro-diffusion process. and cooling water should be in opposite
Due to the limits on pressure that can Faster steam flow rates do not necessary directions at the maximum possible speed.
be built up in the charge vessel, water and mean quicker recovery times. Fabricated The condenser must be sensitive enough to
steam distillation will have only a limited steam boilers cost much more to run than react on the vapour flow very quickly. The
effect on extracting high boiling materials water baths and may lead to high required number of tubes and length of the
from plant materials. However there is less distillation costs, especially if they require condenser depends on the rate of distillate
opportunity for hydrolysis to occur than with petrochemical feed stocks. However if flow, the pressure, the temperature of the
July 2012 P E R S O N A L C A R E 71

6. ESSENTIAL OILS
cooling water and the desired exit microscopic oil droplets. Temperature plays
Distillate in-flow from still
temperature range of the distillate. (water-oil mixture) a crucial role in separation, where it should
The condenser must remove the be moderately warm to increase the
equivalent amount of heat that is needed relative specific gravity differential of the oil
to vaporise the distillate, plus the additional Oil and water. Raised temperature of the
outlet
amount of heat to reach the optimal distillate water will allow the small oil
distillate temperature range of the particles to rise to the top of the separator
condensate distillate exiting the condenser. quicker in a similar manner to the
The rate of which heat would be removed condenser exit temperature range where
from the distillate can be represented by Water there will be an optimal separator water
Internal outlet
the following equation: baffle temperature range to promote oil-water
Q = UA∆t ∆ separation.11
Where Q = the heat removed by unit During distillation, the more volatile
of time constituents tend to vaporise quicker and
U = a constant determined by the less volatile constituents vaporise later
operating conditions (condensing and in the distillation. This leads to an oil that
cooling made up of a number of will vary in constituents during the
factors) usually a constant is used. distillation period. By changing separation
A = the area available for heat flasks at particular points during a single
removal distillation, oils of different constituent
∆t = the temperature difference profiles can be collected. This is important
between the vapour and the cooling Figure 5: Schematic view of a hydro-diffusion in ylang ylang and lavender distillation,
medium. distillation system. where different oils profiles will have
different uses and values to particular
U is made up of a number of factors possible separate the oil from the distillate customers. Many distillers also use this
including the flow rates of cooling water water. As distillate water volume is much principal to collect specific fractions during
and vapours, the material that the greater than oil, it is important that water the distillation, which can later be blended
condenser is constructed, and usually a can be removed continuously. Oil and together to create a whole oil that meets
constant is used due to the difficulty to water separates according to specific with certain specific specifications, such as
calculate. The value of U increases as gravity forming two layers. Lighter than a standard.
these factors increase. Thus according to water oils will float to the top and heavier The water distillate will always be
the equation, the surface area can be as than water oils will sink to the bottom. This saturated in oil and directly dumping it
large or small as desired, as long as the must be considered in separator design for would lead to a loss in yield. For this
other factors compensate. However the water removal. reason some distillers (water and water and
overall capacity of the distillation system If the specific gravity of oil and water is steam distillation) will channel the water
will have great bearing on the condenser very close, the two components will not distillate back into the still vessel for re-
area. Condenser sizes will also vary in size separate immediately. Distillate flowing into distillation in what is called cohobation,
according to the temperature of available the separator must therefore not disturb mentioned previously. For this purpose the
cooling water on site, thus condensers in the surface area and flow into the body of separator must be placed higher than the
temperate and tropical areas will reflect the water to prevent surface turbulence. still vessel proper so distillate water in the
this in size. The separator must also be large enough separator can be fed back into the still
Using a condenser system with the so that drained water does not carry away through gravity.
wrong capacity for the distillation system
will have a number of operational
Steam inlet
consequences. A too efficient condenser
system will deliver the distillate at a
temperature below the optimum range,
which could lead to cool air outside being Downward steam flow
sucked into the system. This outside cooler
air in the condenser tubes could create
expansion and contraction of vapours in Plant material
the condenser leading to splattering and
Side opens so that
intermittent distillate outflow. This could cartridge with plant
also occur if the cooling water is too cold. material can slide in Grated base
If the condenser is too small for the and out of still
distillation system, then the still must be
operated with lower steam rates, which
Condenser array
would lengthen distillation times and open
up the possibility of hydrolysis to occur
within the vessel.
Water and oil collector
The separator system
Before leaving the subject of distillation in
this chapter, some words about the Collector vessel
separator system must be mentioned. The
function of the separator is to as quickly as Figure 6: Oil separator design used in Perlis, Malaysia.
72 P E R S O N A L C A R E July 2012

7. ESSENTIAL OILS
Hydro-diffusion material near the bottom may also lead to 6 Guenther E.The Essential Oils, Volume One:
distillation hydrolysis and lead to lesser yields. History – Origin in Plants, Introduction – Analysis,
Hydro-diffusion distillation is a variation on However, hydro-diffusion distillation appears Malabar, Florida, Robert E. Krieger Publishing
steam distillation where steam is popular within the aromatherapy industry in Company, P 110, 1948.
.
introduced on the top of the vessel and Europe. PC 7 Fleisher A. Water-soluble fractions of the
condenses through the plant material in essential oils, Perfumer & Flavorist 1991;
the still, where the distillate is collected ɀ The final article in September will 16 (3): 37-41.
and condensed under the plant material conclude with a brief discussion about 8 Bouzid N, Toulgouate K, Villarem G, Gaset A.
which rests on a grill or perforated tray. applying these principles. Analyse quantitative des fractions d’huile
Through steam travelling down the still, essentielle pouvant co-exister lors
there is more time for the volatiles and References d’hydrodistillation de plants aromatiques,
fatty acids floating on the plant material. 1 Johannes AK, Scheffer JC, Svendsen AB. Rivista Ital Eppos 1997; 79: 15-25.
In the case of wood and seeds that have Comparison of Isolation Procedures for Essential 9 Boland DJ, Brophy JJ, House APN. Eucalyptus
many high boiling compounds, which are Oils, Z. Lebensm. Unters. Forsch, Vol. 168, Leaf Oils: Use, Chemistry, Distillation and
difficult to vaporize in an ordinary still, this 1979, pp. 106-111. Marketing 1991; Melbourne, Inkata Press, P .
system may be effective. This would be 2 Private communication with Mr. Jon Bonnardeaux 191.
valuable when fatty acids contribute to the of Western Australia Department of Agriculture, 10 Unpublished private work on tea tree distillation
flavour of a material and it is desirable in early 1990s. at Batu 9, Berseri, Perlis, Malaysia during
the oil. Thus, hydro-diffusion distillation 3 Denny EFK. Field Distillation for Herbaceous Oils, 2004/5.
may return an oil more representative of Lilydale, Tasmania, Denny McKenzie & 11 Hughes AD, (1952), Improvements in the Field
the plant’s natural profile.12 Associates, P 81, 1990.
. Distillation of Peppermint Oil, Corvallis,
It is reported that hydro-diffusion 4 Kristiawan M, Sobolik V, Al-Haddad M, Allaf K. Engineering Experimental Station Bulletin No. 31
distillation gives quicker distillations with Effect of pressure drop on the isolation of 1952; Oregon State College, 1-64.
lower steam consumption than cananga oil using controlled pressure drop 12 Legast E, Peyron L. Hydrodiffusion Industrial
conventional steam distillation.13 However process, Chemical Engineering and Processing Technology to Produce Essential Oils by
this process is governed by the physical 2008; 47 (1): 66-75. Steam, in Proceedings of the 11th International
laws that govern any other type of 5 Rezzoug SA, Boutekedjiret C, Allaf K. Congress of Essential Oils, Fragrances
distillation and the fact that the steam Optimization of operating conditions of rosemary and Flavors Vol. 2 1989; New Dehli, India,
travels downwards while cooling may affect essential oil extraction by a fast controlled 69-73.
the transfer of latent heat and thus pressure drop using response surface 13 Hall R, Klemme D, Nienhaus J. The H&R Book:
increase, rather than decrease distillation methodology, Journal of Food Engineering 2005; Guide to Fragrance Ingredients Vol. 4 1985
time. The tendency to saturate the plant 71 (1): 9-17. London, Johnson Publications, P 13. 0
.
July 2012 P E R S O N A L C A R E 73