Essential Oils: Distillation & Expression Essential oils are produced in the cells of aromatic plants and are held in specialized glands. They are released from the plant and collected (concentrated) most often through steam distillation (and sometimes hydro or water distillation or a combination thereof). Distillation is a method of separating components based on differences in volatile constituents in a heated mixture. Steam distillation involves bubbling steam through the plant material. The temperature of steam is easy to control, making it ideal for heat-sensitive essential oils. The essential oils contained in plants are immiscible in water and have a higher boiling point, allowing the essential oil to vaporize at a lower temperature than it normally would on its own. Other methods used to create pure essential oils are dry or vacuum distillation, dry/destructive distillation, and expression (for citrus peels). Expression, also referred to as "cold pressed", is a method where oil is obtained by using high mechanical pressure to literally squeeze the oil from the plant material. CO2 Extracts: Solvent Extraction 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 terpene esters or the loss of terpene 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, a "select" or "total" extract 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. 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. Other benefits of CO2 extracts: ·the extraction process happens at lower temperatures than steam distillation (up to 40˚C / 104˚F) ·carbon dioxide is nontoxic, odorless, and is easily removed from the extracted oil at the end of the process they are more stable and have a long shelf life they contain no carbohydrates, inorganic salts, proteins/allergens, or germs they meet strict heavy metal requirements CO2 extracts CO2 extracts display some of the characteristics of both essential oils and absolutes. They are extracted using CO2 (carbon dioxide) gas under pressure at ambient temperatures. Depending on the pressure used, a select or total extract will result. Select means that a lower pressure is used and total means that a higher pressure is used. Select extracts are more similar to essential oils in that they are usually fully mobile liquids and essential oils make up the vast majority of the extract. Total extracts contain more constituents of the plant and are more full-spectrum or more closely resemble the constituents of the whole plant rather than just the essential oil fraction of the plant. Because of the purity of CO2 extracts and because they display some very favorable characteristics not found in essential oils, CO2 extracts are primarily used by the food, body care, and herbal industries, yet CO2 extracts are also excellent for aromatherapy and natural perfumery. This extraction technique (more accurately called supercritical CO2 extraction) is a relatively new and expensive technology that is more efficient in some ways than steam distillation because the process has the ability to capture a broader spectrum of the plant components, giving a fragrance more true to the original plant material without the use of chemical solvents. Other benefits are that the extraction process happens at lower temperatures than steam distillation and that carbon dioxide is nontoxic, odorless, and is easily removed from the extracted oil at the end of the process. Characteristics of supercritical CO2 extraction of oud oil Essential oil of oud is a mixture of many chemical components, which is more complex. The following is a summary based on the relevant literature, some of which have not been tested by empirical methods. The volatile components in essential oil of oud can be analyzed by gas chromatography. It mainly consists of alopecuroic acid, alopecurol, alopecurol spiral aldehyde, alopecuron sesquiterpenoids, dehydroalopecurol and isoalopecurol. These components exist in essential oils obtained by steam distillation, solvent extraction and supercritical extraction. Non-volatile components in essential oil of oud include a variety of chromones, triterpenoids, karaoke and furoic acid. These components usually occur in extracts and crude oils obtained by solvent extraction and supercritical extraction. The products obtained by water vapor distillation only contain the high volatile components in Alpinia officinalis, so they were not monitored. Chromosome is an important sign of aloe fragrance. In the research of artificial promotion of aroma, the method of detecting chromone is usually used to detect the effectiveness of a method of artificial promotion of aroma.