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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