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.
Types of distillation used:
- Cold Pressing or Expression
- Water and steam
- Direct steam
- Solvent Extraction
Distillation is basically soaking,
pressing, producing steam, or the use of solvents to remove the essences
from the herbs!
- The first
method is simple Water distillation - 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. Another
example of an oil prepared by this method is turpentine gum. Turpentine
gum is collected from a species of Pine (Pinus palustris) and the gum,
wood chips and pine needles are placed in the distilling chamber with rain
water. This mixture is heated until the plant and oil are condensed in the
condensing chamber. Turpentine oil is not affected by very excessive heat.
- The second method is 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
- The third method is 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.
- The fourth 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.
- The fifth method
is direct Steam Distillation - The steam is hotter and passed through the plant
material at a higher pressure. This method is used for fresh plant
material that has a high boiling point such as seeds, roots and wood. It
is also used for fresh plant material such as peppermint and spearmint.
The crop is cut and placed in a metal distilling tank on a truck. It is
then taken to the distilling tank on the truck. Steam is forced through
the fresh herbs and the oil droplets are carried by the steam through a
vapor pipe at the top of the tank onto a cool condensing chamber. The steam carries the Essential
oil from the plant in suspension which means the droplets of Essential oils are
not dissolved in the steam but remain separate as droplets of oil. When the
steam is cooled it reverts to the liquid state which is water and in most cases
the oil floats on the surface of the water. The oil is then separated from the
water by dripping or pouring.
- The sixth method of
distillation is 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. 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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