CO2 extracts display some of the characteristics of both essential oils and absolutes. Like essential oils, they contain many beneficial therapeutic properties. But unlike absolutes, they are not extracted with petrochemical solvents such as hexane. Instead, they are extracted with CO2 (carbon dioxide) gas under pressure at ambient temperature. Under normal atmospheric conditions CO2 is a gas, but when highly compressed it becomes supercritical – neither a gas nor a liquid.
Supercritical CO2 is an excellent organic solvent that is used to extract aromatic oils from plants. The procedure is fast and gentle and is completely enclosed to prevent the presence of oxygen, thus preserving the composition of the chemical constituents. Highly volatile top notes are not lost, and the bottom notes of less volatile and sensitive oxygenated sesquiterpenes are fully preserved as well. Hydrolysis of monoterpene esters or the loss of monoterpene alcohols in the heart notes is also largely avoided during extraction. Another impressive benefit of CO2 extraction is that once the oil is extracted from the plant material, the supercritical CO2 is returned to its gaseous state at normal air pressure, quickly and completely dissipating and without generating toxic waste.
Depending on the pressure used, ‘select’ or ‘total’ extracts will result. Select extracts are created at lower pressures and are more similar to essential oils, being fully mobile liquids with mostly volatile constituents making up the vast majority of the extract. Total extracts are created using higher pressures and contain more higher molecular weight, lipophilic constituents of the plant, can be thicker or waxier, and more closely resemble the whole plant rather than just the essential oil fraction of the plant. Some CO2 total extracts are, in fact, carrier oils – e.g., Pomegranate Seed CO2 and Rosehip Seed CO2 .
Because of the stability and versatility of CO2 extracts, and since they display some very favorable characteristics not found in essential oils, they are enthusiastically used by food, body care, and herbal product manufacturers. The attractiveness of supercritical CO2 extraction is shown by the already existing industrial applications of natural hop extraction, decaffeination of tea and coffee, defatting of cocoa powder and extraction of herbs and spices, to name a few. But with wider availability these extracts are now finding enthusiasts in aromatherapy and natural perfumery.
Major benefits of CO2 extracts:
- occur at lower temperatures (up to 40˚C / 104˚F) than steam distillation
- carbon dioxide, acting as the solvent, is nontoxic, odorless, and is easily removed from the extracted oil at the end of the process
- have more stability and a long shelf life
- contain no carbohydrates, inorganic salts, proteins/allergens, or germs
- meet strict heavy metal requirements