Essential oils are volatile essences extracted from aromatic plants. Among all the species in the plant kingdom, only 4,000 contain aromatic essences. Nevertheless, only a few hundred contain enough to extract essential oils with a significant yield. Essential oils are complex mixtures of different compounds (terpenes, alcohols, ketones, aldehydes) that provide many benefits, whether ingested, inhaled or applied topically. Let's discover together the different methods of extraction of essential oils.
How are Essential Oils Obtained?
- Steam Distillation is the Most Common Process for Obtaining an Essential Oil
- The Mechanical Pressure, the Method of Obtaining Citrus Essences
- Solvent Extraction, a Process That is Often Not Very Environmentally Friendly
- Supercritical CO2 Extraction, a Modern and Ecological Method
Steam Distillation is the Most Common Process for Obtaining an Essential Oil.
Even though there are several processes for extracting essential oils from aromatic plants, low pressure steam distillation is the most common technique. Invented in the 11th century, it involves several steps.
The water is boiled, and the steam produced is collected.
The plant material to be distilled (flowers, leaves, roots, seeds...) is placed in a copper or stainless-steel tank called an alembic.
Under low pressure, the steam is sent into the still and passes through the plant material to be distilled. This breaks down the aromatic sacs of the plant and isolates the compounds.
he aromatic molecules are carried up the still by the steam to the swan neck. This steam, loaded with essence, passes through a pipe called a serpentine which is bathed in a bath of cold water.
The steam cools and condenses to a liquid state, which is recovered in a decanting vessel, also called a florentine or essencier. The essential oil in on the surface of the liquid recovered. It is lighter than the water used for its extraction, which is none other than hydrosol.
Note: Hydrodistillation is a similar process except for one difference: Initially, the plant material and water are not separated but heated together directly in the same tank (alembic).
The Mechanical Pressure, the Method of Obtaining Citrus Essences.
This is the simplest way to obtain an essential oil. It simply uses mechanical pressure to burst aromatic sacs manually. The essence and water are then simply separated by cold decantation. This process is mainly used to extract essential oils from citrus fruits such as lemon, yellow and green mandarin, lime, bergamot or orange.
Solvent Extraction, a Process That is Often Not Very Environmentally Friendly.
This technique is particularly widespread in the perfume industry because it produces compounds with a very pronounced smell. It consists of mixing the plant material with a solvent in a tank and heating the mixture. The solvents are varied (petroleum ether, methanol, ethanol, hexane...). This extraction technique is quite controversial because it is not very environmentally friendly. Moreover, it is possible to find traces of solvent in the substance obtained through this method.
Supercritical CO2 Extraction, a Modern and Ecological Method.
Even though this method of extraction is very expensive, it provides essential oils of very high quality (biochemical composition almost similar to the original essence of the plant). The principle is simple: the plant material is crossed by a flow of carbon dioxide (CO2) which increases the pressure and allows the aromatic sacs to burst "naturally".
In addition to being clean and profitable, one of the added values of this technique is that the recovered essential oil can retain its "organic" designation in future products.
Zarith Asyikin Abdul Aziz & al., Essential Oils: Extraction Techniques, Pharmaceutical And Therapeutic Potential - A Review, Current Drug Metabolism, (2018).
Hesham H. A. & al., Techniques For Extraction of Essential Oils From Plants: A Review, Australian Journal of Basic and Applied Sciences, (2016).