The way in which oils are extracted from plants is important because some processes use solvents that can destroy the therapeutic properties.  The usual method of extraction is through steam distillation.  After extraction, the properties of a good quality essential oil should be as close as possible to the "essence" of the original plant.  The key to a 'good' essential oil is through low pressure and low temperature processing.  High temperatures, rapid processing and the use of solvents alter the molecular structure, will destroy the therapeutic value and alter the fragrance.

Early efforts at extraction used alcohol and a fermentation process.  Nowadays, a reputable distiller will try to preserve the original qualities of the plant, but the final therapeutic result is often not formed until after the extraction process.  During extraction, the qualities of the oil change to give it more value - for example, chamazulene (characteristic of the pure blue colour of German Chamomile) is formed during the steam distillation process.

Extraction
Essential oils are extracted from plant material.  Each oil has many chemical compounds within it which vary according to climate, location, soil, methods of cultivating and harvesting.  Essential oils are extracted from plant material by 4 main methods:

	Steam distillation
	Solvent extraction
	Expression
	Enfleurage

Solvent extraction
Where solvents and alcohol are mixed with the plant material in order to produce an absolute, or very high quality flower water.  True essential oils are not produced in this way and there is some dispute as to their use in aromatherapy.

Expression
Used with citrus oils to make 'essences'.  The oils are extracted from the fruit by machinery which mechanically squeezes the oil from the peel, a process called scarification.

Enfleurage
An intensive and traditional way of extracting oil from flowers.  The process involves layering fat over the flower petals.  After the fat has absorbed the essential oils, alcohol is used to separate and extract the oils from the fat.  The alcohol is then evaporated and the essential oil collected.

Steam distillation
A process where steam is passed over the plant material.  The steam is then condensed again, the liquid is collected, and the essential oil separated from the liquid.  The most pure essential oils are collected in this way.

   Photograph of a steam distillation unit used at the Burren Perfumery, Ireland.