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The Making of Essential Oils - Steam Distillation, Absolutes, and CO2s Explained
   
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Aromatherapy Goes 'High Tech'
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.
Steam and Hydro Distillation
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
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Absolutes
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.
CO2's and SCO2's
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.
Cold Pressing
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.
Conclusion
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.
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
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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.
About the author:
Misty is a Naturopath and Yoga Teacher in Boulder, Colorado. She
is a fan of pure
wildcrafted and organic essential oils, and employs them in
her practice.