Essential oils are created using two main methods of extraction – distillation and expression. Essential oils are the concentrated liquid that contains the volatile aroma compounds that have been distilled from plants.
Another similar product, Absolute oil (highly aromatic liquids extracted from plants), is extracted via solvent extraction or enfleurage. Also available on the market are CO2 extracts, which differ in chemistry from essential oils but are increasingly popular.
The most common method for essential oil production is through steam distillation. Steam is passed through raw plant materials causing them to release their aromatic compounds.
These rise with the steam into a cooling chamber. As the steam and plant vapor cools, the vapor turns back into liquid, which separates into water and the essential oil. The water contains the water-soluble parts of the plant, and is known as floral water or hydrosol. Hydrosols are commonly used in cosmetics to moisturize the skin.
The advantage to using distillation for essential oil extraction is that the volatile components can be distilled at temperatures lower than the boiling point, avoiding denaturing the plant, and the product is easily separated from the water.
For plants that can withstand higher temperatures, other methods of distillation such as hydro-distillation (submerging the material in water) or hydro-diffusion (forcing steam in from above the plant material) can be used. Distillation is considered to be the only method to produce pure essential oils.
Some essential oils, namely citrus oils, are obtained through expression – also known as cold-pressing. In the past, expression was done by hand by first soaking the peels in warm water and then pressing them with a sponge. The sponge was then pressed over a container and allowed to stand for the juice and oils to separate. In today’s modern method, the peels are punctured to release the oil and then mechanically pressed. The resulting liquid is then centrifuged where it separates into citrus juice and essential oils.
Since long ago, delicate flowers have been processed using enfleurage to capture their essence. The flowers are combined with animal fat and pressed between pieces of glass. These flowers are then continually replaced with fresh ones until the fat contains the desired aroma. This process has been mostly discontinued because of its use of animal products, but it is still practiced as an ancient art in the Grasse region of Southern France.
The process of solvent extraction is reserved for plant materials that are too delicate to be distilled, particularly delicate flowers such as jasmine. The plant materials are dissolved in a solvent such as benzene or dimethyl ether. The solvent is then evaporated off leaving behind plant oils referred to as “absolutes”. Absolutes are highly concentrated aromatic substances that resemble the natural aroma of the plant and are more colored and viscous than essential oils. These are most often used in the cosmetic and perfume industries due to their strong aromas. Aromatherapists tend to shy away from absolutes in favor of the more pure essential oils in case some of the solvent remains in the final product.
A newer and increasingly popular solvent extraction uses carbon dioxide (CO2). When CO2 is subjected to high pressure, the gas turns into liquid. This liquid C02 will extract the aromatic molecules in a process similar to the solvent extraction for absolutes. When returned to regular pressure, the CO2 simply reverts to gas leaving no solvent residue behind. C02 extraction has been used to extract essences of some aromatics that don’t yield essential oils such as rose hip or calendula. CO2 extracts have a richer more intense scent and can contain some elements not found in their essential oil counterparts.
As you may have been able to ascertain from this article, there really is not one best way to produce essential oils. Depending on the starting material, some methods are better than others. For citrus fruits like orange and lemons, which have a large amount of essential oils present in the skins of the fruit, expression is more than suitable of a procedure. For more delicate ingredients like jasmine, a more complex extraction method is used. There are also more than one way that companies produce oils using each of the methods above, resulting in varying quality of the finished oil. That is to say, not all essential oils are created equally. We've done the research and have ranked the best brands in this article for you to do your homework from! Enjoy!