Distillation Process
Steam Distillation
The most important production method for Essential oils is distillation. The basic principle of distillation is the same but it is carried out in different ways depending on the botanical material and the condition of the material.
Three types of distillation are used:
- Water
- Water and steam
- Direct steam
Water distillation is used when the plant material has been dried and will not be damaged by boiling. It is also used for powdered materials such as powdered almond, and flowers, such as orange and rose, that need to float freely as they tend to lump together when just steam is passed through them. The material comes into direct contact with the boiling water and much care needs to be taken that the water does not boil away and cause the plant material to burn. This mixture is heated until the plant and oil are condensed in the condensing chamber.
The second method of distillation is water and steam. This is used for either fresh or dried plant material that would be damaged by boiling. The plant material is supported on a perforated grid. The water level is below the grid and low pressure, wet steam passes through the plant material. The most important aspect of this method is that the steam is never really hot and always at low pressure. Cinnamon and clove oils are prepared by this method.
In this process steam is passed through plant material which can be anything from wood to flowers, and which has been pressed tightly and evenly in a still. The heat of the steam bursts open the membrane of the oil receptacles in the plant and the volatile plant oil molecules are released into the steam. The steam rises and takes with it hydrophobic, and hydrophilic molecules. When this mixture of water and various other molecules of the plant components separate back into liquid by means of being condensed, it produces two types of natural chemical cocktails. A hydrolat is produced by the distillation process, so that in effect we have two distinct products from distillation of plants, i.e. essential oil and distillate, (hydrolat).
These separate into hydrophilic molecules suspended in water, making hydrolats, and hydrophobic molecules making essential oils. The hydrolat forms the larger part of the two. A good quality water must be used in order to produce wholesome products and some distillers use mountain spring water. High quality and unadulterated plant material makes sure the end result is pure enough to be used therapeutically in certain health care settings and in the home. The distillation process itself is carefully undertaken, not only with regards to the materials used but also that the temperature is not too hot nor too cold and timing is not too short neither too long.
Some distillers only take off the first few litres in the belief that these are the purest. Hydrolats can be made stronger by a process known as cohobation. This entails the hydrolat being recycled through the distillation process several times. At the end the finished creation is a saturated, solution many times stronger than when first siphoned off.
Heat from the Distillation process can at times change the natural
compositions found within the botanic and may even manufacture new components of
immeasurable benefit. An example of this is Chamomile, in which distillation
creates ‘chamazulene’, the primary anti-inflammatory component for which
chamomile essential oil is known.
Cold Pressing or Expression:
This method is mainly used to prepare citrus oils such as orange, lemon and tangerine. One method involves puncturing the oil glands by rolling the fruit over sharp projections that actually pierce the oil glands. The fruit is then pressed which removes the oil from the glands. It is then washed off with a fine spray of water.
The juice is extracted by another tube. The oil is then separated from the water by rotating it at a very high speed. Another method involves separating the peel from the fruits and then cold pressing them. The Essential oil is collected along with small amounts of juice, which is separated.
Enfleurage:
This is an old method which was used in the production of perfumes and pomade extracts for perfumery. Flower petals such as rose or jasmine are layered onto warm oils, cold fat or wax. This process is repeated each day until the base is saturated with the Essential oil. The resulting waxes or pastes contain up to 1 percent of Essential oil. The Essential oil is then extracted from the wax with a volatile liquid such as ethyl alcohol. In the final step the ethyl alcohol is evaporated at low temperatures and reduced pressure so that the pure Essential oil remains as a fairly thick liquid. Cold enfleurage has the advantage that even the most delicate components of the flower oils are preserved. The disadvantages are that it is not very effective and it is very expensive. Flower oils prepared with this method do not contain terpene-hydrocarbons, which indicates that these compounds are not present as such in the flower, but form during distillation.
Solvent Extraction:
This is the most widely used modern method to prepare oils from flowers. The petals are mixed into a volatile solvent such as petroleum, ether or benzene, until the Essential oil is completely dissolved in the solvent. The solution is then filtered and the solvent is evaporated at reduced pressure. The result of solvent extraction is a concrete. The solvent is removed from the concrete by vacuum pressure without the use of heat to avoid any harmful effect to the oil. The concentrated essence that results is called an absolute. Absolutes are highly concentrated flower products without the natural waxes.
CO2 extraction .. coming... soon..
The main advantage of extraction over distillation is that uniform temperatures are maintained throughout the process. High temperatures during the distillation process can produce altered chemical composition of the oil which alters the natural odor. However, this method is expensive compared to distillation, and chemicals or solvents used in the process may still be present after evaporation.
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