Making Essential Oils: CO2's, Hydro Distillation and Absolutes Explained

Yes, even the age-old manufacture of pure essential oils is going high-tech. New modern distillation methods are entering the mainstream, offering wonderful new choices to aromatherapy enthusiasts and natural health professionals. What are these new methods, and more importantly, do they make better essential oils? More therapeutic? Nicer smelling? Well, for most varieties, the oils are simply ‘different' – not necessarily ‘better'. For a few select oils, these new techniques MAY produce a more healing oil, and for others, the oils produced will truly add to the palate of the natural perfumer. Here's a quick look at all the major distillation methods in use today…

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. Oils used in therapeutic aromatherapy are really very chemically-intricate liquids; every oil consists of many individual molecular components which synergize to create the oil's overal biological action and wonderful scent. 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 distillation vessel's temperature needs to be carefully monitored and controlled so that the more delecate volitile compounds are preserved. 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. In addition, the duration of the distillation needs to be precisely monitored for each oil variety - not too long and not too short. This ensures all the important oil components are released, but the resultant oil is not 'overcooked', sometimes resulting in an unpleasant 'medicinal' scent.

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. The volatile components are often too fragile, or too difficult to extract using other means. 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 solvent is removed using a simple vacuum process, leaving only the essential oil behind. The use of solvents in the extraction process notwithstanding, absolutes can have incredibly deep and complex aromas. The new high tech distillation methods include: 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.

Last but not least is the expeller pressing of essential oils from the rinds of ripe fruits like lemons, limes, oranges and grapefruits. 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. Some varieties do very well with the new cold extraction methods; the resin oils like Frankincense and Myrrh may actually be more healing when made this way, and the oils of spices like Cardamom and Black Pepper can be more 'full bodied' in their scent. This likely translates to greater therapeutic properties.

Producing essential oils of aroma-therapeutic grade is skill requiring years of experience. Making an equisite essential oil of any variety demands experience and know-how at every step of the way, from growing and harvesting the plant material to closely monitoring the distillation itself. 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.