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 essential oil, 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.
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 oil and
Rose oil 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 oil –
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 oil, Orange oil , Lemon oil , 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.
Which Method is Best?
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
oil, 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 oil and
most of the 'spice' oils being good examples where a little something
special is present in the aroma. This likely translates to greater
therapeautic properties.
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.
