How are essential oils obtained?

Even though there are several methods of extracting essential oils from aromatic plants, the low-pressure steam distillation is the most common technique used to extract essential oils from plants. Invented in the 11th century, it involves several steps.

1. The water is brought to a boil within aboilerto capture the steam produced.

2. The plant material to be distilled (flowers, leaves, roots, seeds...) is placed in a copper or stainless steel container known as a still.

3. Under low pressure, steam is sent into the still and passes through the plant material to be distilled. This causes the aromatic sacs of the plant to burst and isolates the compounds.

4. Aromatic molecules are driven upwards through the still by steam until they reach the swan neck. This steam, laden with essence, passes through a pipe known as a coil which is immersed in a bath of cold water.

5. The steam cools and condenses back into a liquid state, collected within adecantation vessel, also known as a Florentine flask or essencier. Floating on the surface of the recovered liquid is theessential oil, lighter than the water used for its extraction, which is none other than thehydrosol.

Note: Thehydrodistillation process is almost similar with one difference: initially, the plant material and water are not separated but heated together, directly in the same vessel (still).

This refers to the simplest method of obtaining an essential oil. It simply involves a cold mechanical pressure to manually burst the aroma sacs. The essence and water are then simply separated by a cold decantation. This process is mainly used to extract essential oils from citrus fruits such as lemon, the yellow mandarin and green, lime, bergamot or the orange.

This technique is particularly prevalent in perfumery as it allows for the extraction of compounds with a very pronounced scent. It involves mixing plant material with a solvent in a tank and heating the mixture. The solvents can range in their environmental impact (petroleum ether, methanol, ethanol, hexane...). This extraction technique is somewhat controversial due to its lack of environmental friendliness. Moreover, traces of the solvent can potentially be found in the resulting substance.

Even though this extraction method is very costly, it provides essential oils of extremely high quality (with a biochemical composition almost identical to the original essence of the plant). The principle is simple: the plant material is penetrated by a flow of carbon dioxide (CO2), which increases the pressure and allows the aromatic sacs to "naturally" burst.

Besides being clean and cost-effective, one of the added values of this technique is that the essential oil recovered can retain its designation as"organic"in future skincare products.

• Zarith Asyikin Abdul Aziz & others, Essential Oils: Extraction Techniques, Pharmaceutical And Therapeutic Potential - A Review, Current Drug Metabolism, (2018).

• Hesham H. A. & al., Methods for Extracting Essential Oils from Plants: A Review, Australian Journal of Basic and Applied Sciences, (2016).