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 aroma-therapeutic 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 its place in the making
of aromatherapy-grade essential oils. 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. 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. 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.
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.
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 therapeutic
properties.
Producing essential oils of aroma-therapeutic 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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The author is an ardent supporter of supporting one's
health through natural means. Essential oils are one of
nature's many effective medinces, and the more education
one can receive on using them, the better one can employ
these wonderful remedies. More information is available
through http://www.anandaapothecary.com
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