Lately, it seems that “C02 extracts” are being mentioned on almost every aromatherapy page.
What are C02 extracts? How are they made? Do we even consider them essential oils? To better understand the C02 extraction process, let’s review some other ways that essential oils are obtained. Christina Smith discussed some of these methods previously in her blog post Essential Oil Extraction 101.
Most of the essential oils we know and love are obtained by way of steam distillation, which is done inside of a “still.” The basic process involves four separate parts. Water is heated to boiling in the first chamber. The steam that’s produced is forced into a second chamber containing plant material, such as lavender flowers, peppermint leaves, etc. Essential oil that is found inside plant cells is forced out by the heated steam. The essential oil vaporizes, joins with the steam and is carried across a cooling mechanism called the condenser (blue coil, pictured).
The condenser cools the mixture, which results in a change from a gaseous form (steam) to a liquid state (water and liquid oil). When the vapors condense back into the liquid state, they drip into a third chamber called the condensation or collection chamber. Since we know that oil and water don’t mix, you can guess what happens next. The essential oil layer floats on top of the water layer (hydrosol, also called hydrolat). The two layers can then be separated and bottled. 
Citrus fruits contain essential oil in the glands of the outer peel. Cold-pressed essential oils are obtained from the fruit by mechanically puncturing either the citrus peels or the whole fruit and collecting the expressed liquid. The oil and aqueous (water/juice) layers can then be separated. 
Absolutes are technically not considered essential oils. They are extracted via a multi-step process, and are used with more delicate plant materials (such as jasmine flowers) that wouldn’t survive the heat of steam distillation. As Christina described in her blog post, absolutes are obtained by this process:
1. Plant material is macerated in a solvent, usually hexane
2. After several days the solvent is removed, leaving the viscous, fragrant “concrete”
3. The concrete is dissolved with high-proof alcohol
4. The mixture is chilled, and separates into plant waxes and fragrant tincture
5. The fragrant tincture is vacuum distilled to evaporate off the alcohol, leaving an absolute. [3,4]
Carbon dioxide (chemical abbreviation= “C02”) is a gas familiar to most people: it’s what we exhale during breathing. We breathe oxygen into the lungs during inhalation and exhale carbon dioxide. Carbon dioxide is a waste product of the body’s metabolism. But how does carbon dioxide help produce oil? (Like absolutes, C02 extracts aren’t considered true essential oils, such as those obtained by steam distillation and cold-pressing.)
Under pressure, C02 gas transforms into an “almost” liquid state called the supercritical state. Plant material is placed into an airtight receptacle, and carbon dioxide gas is pumped in under pressure; low heat is also applied to aid extraction. As the pressure inside the container rises, the C02 gas nearly liquifies, bathing the plant material in supercritical C02. The combination of high pressure and low temperatures encourages the plant material to releases its aromatic components. After a period of time, pressure is reduced and the supercritical C02 then changes back to its gaseous state, completely dissipating from the extracted material.
Because lower temperatures are used during the process, heat-sensitive plant components that might be destroyed or inactivated during steam distillation are preserved in the C02 extract. The combination of lower temperatures and (generally) lower pressure means that C02 extracts contain more of a plant’s original constituents than steam distilled oils. According to Dutch aromatherapist Madeleine Kerkhof-Knapp Hayes, the scent of C02 extracted oils is [generally] “richer and more intense because more aromatic components are present”[5 ].
A perfect example of this is a wonderfully aromatic ginger C02 extract carried by Plant Therapy. Steam distilled ginger does not contain the components gingerol or shogaol, which in part give fresh peeled ginger root its characteristic scent. These components are present in C02 extracted ginger, which gives it a more pleasing scent than the steam distilled oil. C02 extracted ginger is also correspondingly “hotter” than steam distilled ginger, so extra caution in diluting it is warranted. Plant Therapy also carries a lovely vanilla C02 and turmeric C02 extracts.
C02 extracts are sub-divided into two categories, “select” and “total.” Select C02s are extracted under lower pressure and resemble essential oils in that they are usually fully liquid. This makes them easier to work with when pipetting or diluting. Total C02 extracts are extracted under higher pressure and contain more of the plant’s original components, including waxes, fatty oils, and color pigments.
Total C02 extractions are more challenging to work with as they are thicker and require special consideration when diluting. Plant Therapy’s C02 products are of the select variety.
We want you to learn as much as you want to about essential oils and how to use them safely. If you have any questions, comments or other concerns, you’re welcome to email us at [email protected] Or come join us on Facebook at Safe Essential Oil Recipes!
Battaglia, S. 2003. The Complete Guide to Aromatherapy. The International Centre of Holistic Aromatherapy, publishers, Brisbane.
Wilson, R. 2002. Aromatherapy-Essential Oils for Vibrant Health and Beauty. Avery publishers, New York.
Pappas, R. 2015. Important Definitions Concerning Aromatic Products. Notes from Essential Oil University Facebook page.
Smith, C. 2014. Essential Oil Extraction 101. www.essentialoilblogging.com.
Kerkhof-Knapp Hayes, M. 2015. Complementary Nursing in End of Life Care. Kicozo publishers, the Netherlands.