Browsing the Aromatherapy market, especially medicinal grade essential oils, you'll find a great many methods of essential oil production. Labels like 'SCO2', 'Hydro-distilled', and 'Absolute' are common, amongst the most popular 'steam distilled' varieties. Some of these methods employ very high-technology equipment, technology that was not available to the average distiller only 25 years ago. Which method produces the best oil? It seems that each distillation process has plants with which it works best, and there's not a 'best way' for making the most healing essential oils. And like many artesian processes, there are many other factors determining an oil's quality: the health and vigor of the plant itself, it's cultivation method (farmed, organic, wildcrafted, etc.), the weather during that growing season, and the skill and intention of the grower and distller. Here's a great review of essential oil distillation techniques used today, so you can understand what you're buying and using when shopping for essential oils...



Steam and Hydro Distillation Production

Steam distillation, the most common method of essential oil production, involves the flow of steam into a chamber holding the raw plant material (Hydro-distillation uses boiling water directly). 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. The oil and water are then separated - the water, or'hydrosol', is often retained for it's own therapeutic properties.

Several parameters determine the quality of a steam distilled essential oil. Besides the quality of the plant material itself, there is the distilling time, temperature, and pressure. Aromatic oils are very complex - each is made up of many distinct molecules which come together to form the oil's aroma and therapeutic properties. Some of these molecules are delicate structures which will be altered by harsh environmental conditions. So, much like a fine meal is more flavorful when made with patience, oils generally benefit from patient processing.

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.

What are 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. Jasmine oil, in fact, is only found as an absolute, whereas rose is available in both an 'otto' (an expensive steam distilled form) and an absolute.

Making an absolute is a two-step process - the 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. This concrete is again processed using alcohol of the type found in beer, wine, etc., in which the wax does not dissolve. 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, only minute quatities of ethyl alcohol should remain. The use of solvents in the extraction process notwithstanding, absolutes can have incredibly deep and complex aromas.

What are CO's and Super Critical CO2's?

And now for the most modern methods, 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.

Carbon dioxide methods have significant advantages. There are no solvent residues left behind, and the resultant product is perfectly pure. 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 species are involved, such as Indian Sandalwood - less of the plant is needed to produce an equivalent amount of oil.

Cold Pressing

Cold pressing from the rinds of citrus fruit proudces oils such as Bergamot, Sweet Orange, Lemon, Lime, and the like. This involves the simple pressing of the peels at about 120 degrees. Little, if any, alteration from the oil's original makup occurs - these oils retain their bright and uplifting aromas, like that of smelling a wonderfully ripe fruit.

Is there a Best Method?

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 well-rounded essential oils is skill requiring years of experience - it takes the work of a dedicated artesian at every step. The making of a great essential oil relies far more on knowledge and experience than it does on the particular extraction method. There are of course legitimate reasons to select one distillation method over another. 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.