The methods used to extract essential oils include distillation, expression, enfleurage, solvent extraction and carbon dioxide extraction. The choice of method depends on the type of plant material, whether flower, herb, citrus or woody; the cost of extraction; and the desired quality of product.
Distillation involves the use of water, steam or both to extract the volatile substances in a plant material and isolate the essential oil from the collected liquid. Expression, also called cold pressing, is the method used for extracting citrus essential oils. Aside from the traditional pressing of soaked rinds, modern methods of expression use prodding and pricking to release and collect the essential oils.
Enfleurage uses cold-fat for extraction, but it is rarely used because of its high cost. The solvent extraction method uses petroleum ether, methanol or ethanol to extract the lipophylic essential oils from delicate flowers, such as jasmine, carnation and mimosa. Carbon dioxide extraction is a relatively new method that utilizes carbon dioxide gas, which turns to liquid under pressure, to extract the aromatic substances from the plant material.