by Misty Rae Cech, ND
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Aromatherapy Goes 'High Tech' |
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New methods of essential oil extraction are entering the mainstream
of aromatherapy, offering new choices in oils never before
available. With the new labels of 'CO2' and 'SCO2', along with the
traditional 'steam' and 'hydro' distillations, 'absolutes',
and 'cold pressing', a little education for the aromatherapy
enthusiast can go a long way in essential oil selection. Is one
process better than another? Does one produce a nicer smelling oil,
or one with greater aromatherapeutic value? It turns out that
essential oil production, like winemaking, is an art form as well as
a science. The value of the newer processing methods depends greatly
on the experience of the distiller, as well as the intended
application of the final product. Each method is important, and has
it's place in the making of aromatherapy-grade essential oils.
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Steam and Hydro Distillation |
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Steam distillation, the most common method of essential oil
production, involves the flow of steam into a chamber holding the
raw plant material. The steam causes small sacs containing essential
oil to burst. The oil is then carried by the steam out of the
chamber and into a chilled condenser, where the steam once again
becomes water. (Hydro-distillation is a similar process where the
plant material is boiled, with the resultant steam being captured
and condensed). The oil and water are then separated; the water,
referred to as a 'hydrosol', can be retained as it will have some of
the plant essence. Rose hydrosol, for example, is commonly used for
it's mild antiseptic and soothing properties, as well as it's
pleasing floral aroma.
A number of factors determine the final quality of a steam distilled
essential oil. Aside from the plant material itself, most important
are time, temperature and pressure, and the quality of the
distillation equipment. Essential oils are very complex products;
each is made up of many, sometimes hundreds, of distinct molecules
which come together to form the oil's aroma and therapeutic
properties. Some of these molecules are fairly delicate structures
which can be altered or destroyed by adverse environmental
conditions. So, much like a fine meal is more flavorful when made
with patience, most oils benefit from a long, slow 'cooking' process.
The temperature of the extraction chamber cannot be too high, lest
some components of the oil be altered or destroyed. The same is true
of the chamber's pressure. Lavender, for example, should not be
processed at over 245 degrees F and three pounds per square inch of
pressure (3 psi). Higher temperatures and/or pressures result in
a 'harsh' aroma – more chemical than floral – and lessen the oil's
therapeutic effects. Also, the extraction period must be allowed to
continue for a certain period of time in order to flush ALL the
oil's components from the plant, as some are released more quickly
than others.
Despite the drawbacks of aggressive processing, high temperatures
and pressures are often used to produces large quantities of oil in
a short period of time. These oils are usually destined for use in
cosmetic and processed food manufacturing, but are sometimes sold to
final consumers as essential oils for use in aromatherapy. These
oils will be less expensive, but are of limited therapeutic value,
and the difference is apparent when the aromas are compared side-by-side. |
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Absolutes |
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Some plants, and particularly flowers, do not lend themselves to
steam distilling. They are too delicate, or their fragrance and
therapeutic essences cannot be completely released by water alone.
These oils will be produced as 'absolutes' – and while not
technically considered essential oils they can still be of
therapeutic value. Jasmine and Rose in particular are delicate
flowers who's oils are often found in 'absolute' form.
The processing of an absolute first involves the hydrocarbon solvent
extraction of a 'concrete' from the plant material, a semi-solid
mixture of typically 50% wax and 50% volatile oil. The concrete is
again processed using ethyl alcohol (the same alcohol found in beer,
wine, etc.) in which the wax is only slightly soluble. The volatile
plant oil separates into the alcohol and this mixture is removed.
The alcohol is then evaporated and the result is an almost pure
plant extract – depending on the care taken in the evaporation
process, sometimes 2% or less of the ethyl alcohol may remain. The
use of solvents in the extraction process notwithstanding, absolutes
can have incredibly deep and complex aromas. |
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CO2's and SCO2's |
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And now for the most modern technologies, Carbon Dioxide and
Supercritical Carbon Dioxide extraction. Both methods involve the
use of carbon dioxide as the 'solvent' which carries the essential
oil away from the raw plant material. The lower pressure CO2
extraction involves chilling carbon dioxide to between 35 and 55
degrees F, and pumping it through the plant material at about 1000
psi. The carbon dioxide in this condition is condensed to a liquid.
Supercritical CO2 extraction (SCO2) involves carbon dioxide heated
to 87 degrees F and pumped through the plant material at around
8,000 psi – under these conditions, the carbon dioxide is likened to
a 'dense fog' or vapor. With release of the pressure in either
process, the carbon dioxide escapes in its gaseous form, leaving the
essential oil behind.
These carbon dioxide methods have a couple of advantages: Like steam
distillation, there are no solvent residues left behind, and the
resultant product is quite pure. Like solvent extraction, there is
no heat applied to the plant material or essential oil to alter it
in any way. The oil produced is very accurate with respect to the
original state of the plant. The CO2 methods also are the most
efficient, producing the most oil per amount of plant (one of the
reasons for the high cost of essential oils is the low yield of oil
from most plants – one ton of Rose petals produces less than 1 pound
of oil, for example). The efficiency of CO2 extraction is
particularly important when rare or endangered plant species are
involved, such as Indian Sandalwood – less of the precious plant is
needed to produce an equivalent amount of oil. |
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Cold Pressing |
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| Finally, there is the 'cold pressing' of citrus oils from the peels
of fruit, as is done with Bergamot, Orange, Lemon, and the like.
This method involves the simple pressing of the rind at about 120
degrees F to extract the oil. Little, if any, alteration from the
oil's original state occurs – these citrus oils retain their bright,
fresh, uplifting aromas like that of smelling a wonderfully ripe
fruit. |
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Conclusion |
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| CO2's, with some obvious advantages, are not always the best choice
for a particular need. They still are the most expensive, despite
their higher yields. The resultant product differs slightly compared
to one produced another way – the oils produced by steam
distillation of some plants may sometimes be found to have a more
agreeable aroma. Patchouli, for example, seems to benefit from the
steam distillation process by becoming a little warmer and richer.
Many other essential oils are quite effectively produced via steam
distillation, with little alteration from the original plant state.
Oils from other plant species do seem more 'complete' with CO2
processing, with Frankincense and most of the 'spice' oils being
good examples where a little something special is present in the
aroma. |
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| Producing essential oils of aromatherapeutic grade is skill
requiring years of experience. It takes the work of a dedicated
artesian at every step, from growing and harvesting to fine-tuning
the distillation process, to produce a truly fine oil. The making of
a fine essential oil relies far more on knowledge and experience
than it does on the particular extraction method. There are,
however, legitimate reasons to select one distillation method over
another – some plants simply require a particular process to produce
a fine oil, and the oil needed for a particular application may only
be made by one process. In the end, as is often the case in
aromatherapy, your own sense of smell can tell you which oil will
work best for you. |
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Misty Rae Cech ND is a practicing naturopath and yoga instructor in
Boulder, Colorado, and the owner of the Ananda Apothecary. She regularly employs
aromatherapy and essential oils with her clients, finding these
botanicals a gentle yet effective means of supporting their health.
For more, see http://www.anandaapothecary.com
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Visit Misty's Website  |
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