Scientific Aromatherapy

Distillation and expression


Distillation process for essential oils

The majority of essential oils are obtained by low pressure steam distillation without using a chemical descaler.

In this process, the steam crosses a tank filled with aromatic plants. The steam extracts the plant essence to form a homogeneous gas mixture. At the tank outlet and under controlled pressure, the essential oil-enriched steam crosses a coil and condenses. The liquid ends up in the essencier (Florentine vase) where the essential oil has a density that is lower than that of water.

Criteria for good distillation :

Criteria for good distillation :

Distillation is a delicate process which calls for experience and constant supervision. To obtain a top quality essential oil, the following criteria must be met :


  • The still : must be made of stainless steel, as copper and iron can form oxides.
  • Low pressure : distillation needs to take place at low pressure, between 0.05 and 0.10 bar, with overoxidation occurring at high pressure. In this way, the color of the common thyme essential oil in full bloom varies from light red to reddy-brown when increasing the pressure. The pyrogenic reaction of wood with bark, which results from high pressure distillation at high temperature gives essential oils that are soiled with carcinogens.
  • Duration of the distillation : it needs to be extended to allow the extraction of the totum from the aromatic molecules, i.e. all fractions that are referred to as "head", "heart" or "tail". For example, three quarters of the common thyme essential oil is extracted during the first thirty minutes, but you require between sixty and eighty-five additional minutes to extract all the phenols. Distillers are paid by the kilogram of essential oil, and that is why some producers distil at high pressure and stop distilling after the profitable 25 or 30 minutes. Very often, these essential oils are then "rectified", i.e. re-distilled to purify them from undesirable components (higher boiling points) and to concentrate the most volatile components. This process produces discolored essential oils with a less refined odor, different properties and increased side effects. In this way, a rectified eucalyptus essential oil can contain up to 80% eucalyptol, but it will be more irritating for the bronchial tubes than a "complete" eucalyptus essential oil which only contains 60% eucalyptol.
  • Water : the water used must be a non-calciferous spring water in order to avoid recourse to chemical descalers.
  • Storage and keeping : after distillation, the essential oils must be filtered and then stored in immutable hermetic tanks stocked in a cool cellar. Their bottling must only take place in brown or blue opaque glass bottles to ensure they are kept away from light and oxygen.


Process for the expression of essential oils


Expression consists in mechanically breaking the "essence pockets" in the fresh zest of citrus fruits to extract the essences.

This method is the simplest but it is only possible with citrus fruits (orange, lemon, bergamot). The product obtained is called "essence" and not "essential oil".


Other extraction methods :

Other extraction methods exist, which we will detail below.

  • Percolation or hydrodiffusion : this method consists in sending steam downwards. It is faster and gives a higher quality of aromatic substances, but charges the essential oils with non-volatile substances. We then speak of "percolation essence".
  • Supercritical CO2 extraction : ultra-modern and highly expensive, this method consists in passing a current of CO2 at high pressure which bursts the essence pockets and brings out the aromatic substances.
  • Enfleurage : enfleurage is normally reserved for flowers containing very low concentrations of essences (jasmine, mimosa etc.). The flowers are put into contact with absorbent fats that gradually become saturated with essence. The ointments thereby obtained are used as they are or exhausted by absolute alcohol. We thereby obtain alcoholic flower extracts referred to as "absolute".
  • Exhaustion procedure : the extraction of the essences can take place using volatile solvents (benzene). We obtain concretes of flowers and leaves which become absolute by alcohol exhaustion and then "concrete essences" after evaporation. Concretes generally contain 2 to 3% residual solvents. These essences are therefore only suitable for olfactory therapy.


To obtain 1 kg of essential oil, you will need :

  • 7 kg of Clove floral buds - Eugenia caryophyllus.
  • 50 kg of Lavendin - Lavandula x burnatii clone reydovan.
  • 150 kg of True Lavender - Lavandula angustifolia ssp angustifolia.
  • 1 ton of Everlasting (Italian Everlasting) - Helichrysum italicum ssp serotinum.
  • 4 tons of Damask’s Rose petals - Rosa damascena.
  • 5 to 10 tons of Melissa - Melissa officinalis.