Essential oils are extracted from plants in a number of ways. Some methods of extraction have been used for centuries. Other methods are more recent. Essential oils are extracted from plants by distillation, expression, enfleurage, percolation and carbon dioxide extraction. Solvent extraction is an additional method of aromatherapy extraction used to create resinoids, concretes and absolutes.
Distillation
Arab physician and scientist Avicenna invented the use of the refrigerated coil to perfect the art of steam distillation in the 11th century, according to Julia Lawless, in "The Illustrated Encyclopedia of Essential Oils". Steam distillation remains the most economical method of essential oil extraction, according to Shirley Price, in "Aromatherapy Workbook".
Steam distillation is a complex process. The plant material is placed in a large vat and water is heated up underneath the vat to produce steam. Essential oil molecules, contained within the sacs of the plant material, evaporate into the steam. The steam is forced along a pipe that passes through a refrigerated coil system. As the steam cools down, the essential oil molecules form a liquid. Essential oils are separated from the water into which they are released because water and the essential oils have different densities.
Expression
Shirley Price writes that the method of expression is used to extract essential oils from citrus fruits, such as lemons and oranges. Citrus fruits have sacs of essential oil located just beneath the peel of the fruit. Expression is squeezing out the essential oil. The process is often carried out within large factories that also produce fruit juice.
Percolation
Percolation is one of the newer methods of aromatherapy extraction. Price writes that the process of percolation works the same way as a coffee percolator works and is similar to distillation. Percolation extraction is quicker than distillation, however, and produces richer essential oils. Percolation is not yet a common method of extraction because not all essential oils are suitable for extraction in this way.
Carbon Dioxide Extraction
Carbon dioxide extraction is also one of the newer methods of aromatherapy extraction. Carbon dioxide extraction uses expensive equipment with carbon dioxide at high pressures and low temperatures. The chemical make-up and properties of essential oils extracted by carbon dioxide is pure, stable and closer to the properties of the original plant, according to Price.
Enfleurage
Enfleurage is a method used to obtain essences from flowers such as jasmine, according to Patricia Davis, in "Aromatherapy: An A-Z". Enfleurage is a traditional method of extraction but it takes days to lay out plant material on large racks, coat them in fat and wait for the fat to absorb the flower petals. The fat is then diluted in alcohol to separate the fat from the essential oil. The method of enfleurage produces what is called an absolute, not a true essential oil. An absolute, however, is also used in aromatherapy for therapeutic purposes.
Solvent Extraction
Solvent extraction is not used to produce essential oils because of the chemicals used in the process of extraction. Solvent extraction produces resinoids, concretes and absolutes that are used in aromatherapy for non-therapeutic purposes, such as perfumery. Lawless writes that fragrance products used in the perfumery industry are usually a combination of essential oils, absolutes, concretes or resinoids.
References
- "The Illustrated Encyclopedia of Essential Oils"; Julia Lawless; 1995
- "Aromatherapy: An A-Z,"; Patricia Davis; 1999
- "Aromatherapy Workbook"; Shirley Price; 2000
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