The extraction using volatile solvents
Extraction using volatile solvents consists of dissolving the fragrance-bearing part of the plant in a solvent which is then evaporated. This technique was practised in the 18th century using ether, which is very expensive and highly inflammable; today more suitable solvents such as hexane and ethanol are used.
The plant matter is placed in extractors, enormous steel vats, and washed in successive quantities of solvents that imbibe the fragrance. After decanting and filtering, the solvent is then evaporated and leaves a highly fragranced paste. This scented mixture is called a concrete when produced from flowers and a resinoid if derived from dried plant matter (roots, mosses etc).
The concrete or resinoid is then washed in alcohol in mechanical beaters and chilled several times, resulting in a pure essence called absolute.