Essential oil: Encyclopedia II - Essential oil - Production

Essential oil - Production

Main high-volume products - turpentine; orange, lemon, mint and citronella are essential oils. Prior to the discovery of distillation, essential oils were extracted by pressing, and this is still the case in cultures such as Egypt. Traditional Egyptian practice involves pressing the plant material, and then burying it in unglazed ceramic vessels in the desert for a period of months to drive out water, the water having a smaller molecular size diffuses through the ceramic vessels while the larger essential oils do not. The lotus oil in Tutankhamun's tomb, which retained its scent after 3000 years sealed in alabaster vessels, was pressed in this manner.

Today, most common essential oils, such as lavender, peppermint, and eucalyptus, are distilled. Raw plant material, consisting of the (flowers, leaves, wood, bark, roots, seeds, or peel, is put into an alembic (distillation apparatus) over water, and the volatile compounds are vaporized as the water is heated. The vapor flows into a cooling tank, and as the steam condenses, the essential oil, which is lighter than water, floats on top. The water is referred to as a hydrosol, hydrolat, or plant water essence. Popular hydrosols are rose water, lavender water, and orange blossom water. Most oils are distilled in a single process. One exception is ylang-ylang, which takes 22 hours to complete distillation. It is fractionally distilled, producing several grades.

Most citrus peel oils are usually expressed mechanically, or cold-pressed. These oils are usually by-products of the large-scale citrus industry, and thus are much cheaper than most distilled oils.

Some flowers contain very little volatile oil, or EO components are too delicate to be distilled. Instead, a solvent such as hexane or supercritical carbon dioxide is used to extract a concrete, or mixture of essential oil and other lipophilic (oil soluble) plant material. The solvent is then removed by distillation for re-use. Then another solvent, often ethyl alcohol, is used to extract the essential oil from the concrete. The alcohol is removed by a second distillation, leaving behind the absolute. Hence these types of essential oils, from plants such as jasmine and rose, are called absolutes.

In supercritical fluid extraction, high pressure carbon dioxide gas (up to 100 atm.) is used as a solvent. This avoids petrochemical residues in the extracted product and is identical to one of the techniques for making decaffeinated coffee.

Adapted from the Wikipedia article "Production", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki