The Making of Essential Oils – Steam Distillation, Absolutes,
and CO2's Explained
by Misty Rae Cech
zone3
The newest high-tech methods of making aromatherapy-grade essential
oils have some great advantages, but with a steeper price. Are they
worth it? It may be up your nose to find out... 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 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 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 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.
ABOUT THE AUTHOR
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