Essential oils are produced from the distillation of aromatic plants (e.g. mint), flowers (e.g. chamomile), seeds (e.g. carrot), woods (e.g. sandalwood), fruits (e.g. a tangerine), or berries (e.g. juniper).
A number of methods are used to extract these aromatic substances. Extracting essential oils is an extremely difficult and delicate task as it seeks to capture the most subtle and fragile byproducts of a plant without altering their quality.
Low pressure steam distillation
The majority of essential oils are obtained by way of low pressure steam distillation.
- Distillation is a delicate process requiring experience and constant supervision. In order to obtain a high-quality oil, distillers must comply with rigorous specifications if they wish to extract the essence of the plant in its pure and unadulterated form.
- The process consists of passing steam through a vat filled with the aromatic plants, flowers, seeds, wood, etc.
- Upon exiting the distillation tank, the pressurized steam enriched with essential oil passes through a coil and condenses.
- An “essencier” (aka a florentine separator) then collects the water and the essential oil. The difference in density between the two liquids makes it easy to separate the essential oil.
Distillation is a delicate process requiring experience and constant supervision. Here are a few tips for producing the highest-quality essential oil:
The alembic: must be made of stainless steel as copper and iron can oxidize.
Low pressure: distillation must be done at low pressure (between 0.05 and 0.10 bars) as high pressure can lead to overoxidation.
Distillation duration: must be extended to allow for the collection of the most important aromatic molecules, i.e. the parts known as the “head,” the “heart,” and the “tail.”
Water: choose spring water with few or no minerals so you don’t have to use a chemical descaler.
Storage and conservation: once the distillation is complete, the essential oil must be filtered and stored in an airtight container in a cool basement. Essential oils should only be stored in opaque brown or blue glass bottles to ensure they are protected from oxygen and light.
For citrus fruit (lemons, tangerines, grapefruit, etc.), another process of obtaining essential oil can be used: cold pressing of the aromatic rinds. Purists refer to these finished products as “essences” and not “essential oils” as the process is free of the steam or solvents that modify the chemical makeup of the product. Due to the extensive use of insecticides on citrus fruit, all Citrus essences intended for consumption must be certified organic.
Other extraction methods
Percolation or hydrodiffusion
This method consists of feeding steam from the top to the bottom. It is faster and improves the quality of aromatic substances but also infuses essential oils with non-volatile substances. These products are referred to as “percolation oils.”
Supercritical carbon dioxide extraction
A modern technique that allows for extraction of essential oils from plants when steam distillation is impossible, this method consists of passing a stream of CO2 at high pressure through aromatic plant materials to burst the essence pockets and extract the aromatic substances.
Enfleurage is usually reserved for flowers with extremely low concentrations of essences (jasmine, mimosa, etc.). The flowers are soaked in absorbent fats that gradually become saturated with essence. The resulting pomades are used as is or dissolved by alcohol to obtain aromatic plant extracts called “absolutes.”
Extraction by solvents
Essences can also be extracted by volatile solvents (benzene). These essences are referred to as “concretes,” which become “concrete essences” once they have evaporated and “absolutes” when they are dissolved in alcohol. Concretes usually contain residual solvents (2-3%). These essences are therefore only suitable for olfactotherapy.
The amount of plant material needed to produce 1 kg of essential oil varies widely by plant :
- 7 kg of clove buds - Eugenia caryophyllus.
- 50 kg of lavandin - Lavandula x burnatii clone reydovan.
- 150 kg of true lavender - Lavandula angustifolia ssp angustifolia.
- 1 ton of immortelle (Italian helichrysum) - Helichrysum italicum ssp serotinum.
- 4 tons of Damask rose petals - Rosa damascena.
- 5 to 10 tons of lemon balm - Melissa officinalis.