Steam distillation and CO2 extraction are two of the most popular extraction methods of essential oils today, particularly because of the speed of the process and how pure the finishing product is when done. You can find more information on the other types of extraction methods in NAHA's blog here.
What is CO2 Distillation?
We hear a lot these days about the use of CO2 extracts in aromatherapy. For those unfamiliar with the CO2 distillation process, plant material is placed into an airtight receptacle and carbon dioxide (CO2) gas is pumped in under pressure. Low heat is also applied to aid the extraction process; temperatures are generally lower than those used during steam distillation. As pressure inside the sealed container rises, the CO2 gas nearly liquifies, bathing the plant material in supercritical carbon dioxide. (The “supercritical” state refers to the point where carbon dioxide is neither a true liquid, nor a gas.) The combination of high pressure and low temperatures encourages the plant material to releases its aromatic components. After a calculated time, pressure inside the vessel is reduced. The supercritical CO2 then reverts back to its gaseous state and completely dissipates from the extracted material.
CO2 extracts are sub-divided into two categories, “select” and “total”.
Select CO2s are extracted under lower pressure and resemble essential oils in that they are usually fully liquid, which makes them easier to work with when pipetting or diluting.
Total CO2 extracts are extracted under higher pressure and contain more of the plant’s original components, including waxes, fatty oils, and color pigments. Total CO2 extractions are more challenging to work with as they are thicker and require special consideration when diluting.
Because lower temperatures are used during the CO2 distillation process, heat-sensitive plant components that may be destroyed or inactivated during steam distillation are preserved in CO2 extracts. A good example of this is the monoterpene alcohol linalool, known for its soothing and relaxing proper-ties. The high temperature, pressure, and extended distillation time used in steam distillation of cinnamon bark essential oil destroys much of the linalool content; in contrast, linalool is found in higher amounts in CO2 extracted cinnamon bark.
What is Steam Distillation?
Today, steam distillation is the most common method used to extract the essential oils from a plant. This type of distillation will produce a very authentic and pure form of essential oil because the process is without the use of chemicals. Dried or fresh (produces most oil) plant material is placed into the still while water located in a different still is brought to a boil, creating steam. This steam travels to the still containing the plant material which puts pressure on the plants cells and sacs, causing them to open and expel the essential oils. The essential oils then rise with the steam reaching the condenser where everything cools so that the oil and water can separate.
Steam distillation also produces another element, known as floral waters or hydrosols. Learn why hydrosols are becoming increasingly popular and about their therapeutic benefits in the Institute's blog here.
Steam Distillation or CO2 Extraction?
Practically speaking, what does this mean for aromatherapists? CO2 extracts often have a longer shelf life because they contain more of the original plant material’s non-volatile waxes, pigments, and resins. This is particularly true for black pepper (Piper nigrum) oil. As a steam-distilled product, the terpene-rich oil oxidizes fairly quickly and the by-products of oxidation can be very irritating to skin and the lungs. CO2-extracted black pepper oil contains piperine, a Carbon-17 alkaloid compound that from a clinical perspective enhances anti-inflammatory and anti-arthritic properties of the oil. Piperine is not detectable in steam-distilled black pepper essential oil.
German chamomile (Matricaria recutita) is another popular CO2 extract. German chamomile essential oil is blue in color as it contains chamazulene, a sesquiterpene noted for its anti-inflammatory effects. This compound forms during steam distillation from its chemical precursor, matricin. While CO2 extracted German chamomile contains no chamazulene (since it is not steam-distilled), it contains high levels of matricin, thought to possess even better anti-inflammatory effects than chamazulene.
CO2 extracts are a fast-growing wave of the future in aromatherapy, as extended shelf life and faster extraction times make them a popular choice. To learn more about how to incorporate aromatherapy and essential oils into your growing practice, check out the Institute's blog on aromatherapy education and essential oil classes here.