Extraction of essential oils

Since any part of a plant may produce essential oils, the method of extraction depends upon the site and accessibility of the essence in each particular case.

The oils are produced by special minute cells or glands and are released naturally by the plant in small amounts over a prolonged period of time when needed.

In order to harvest the oils in appreciable amounts, it is usually necessary to collect a large quantity of the part of the plant needed and to subject the material to a process that causes the oil glands to burst.

One of the most common methods is steam distillation. The plant material is paced tightly into a press or still and steamed at a high temperature.

This causes the oil glands to burst and the essential oil vaporizes into the steam.
This is then cooled to separate the oil from the water. Sometimes water is used for distillation rather than steam.

Another method involved dissolving the plant material in a solvent or alcohol and is called solvent extraction.

This involves placing the material in a centrifuge, which rotates at high speed, and then extracting the essential oils by means of a low temperature distillation process. Substances obtained in this way may be called resins or absolutes.

A further method is called maceration in which the plant is soaked in hot oil. The plant cells collapse and release their essential oils, and the whole mixture is then separated and purified by a process called defleurage.

If fat is used instead of oil, the process is called enfleurage. These methods produce a purer oil that is usually more expensive than one obtained by distillation.

The essential oils used in aromatherapy tend to be costly as vast quantities of plant material are required to produce them and the methods used are complex and costly.