Essential oils are highly concentrated plant oils. Most essential oils are extracted through a distilling process, a process involving steaming the plants to release their oils. The steam takes the essential oil with it into a condenser, which cools the steam. As the steam cools, the oil floats to the top of the remaining water. The leftover water still contains some of the plant chemistry and is often called floral water (or hydrosol), used for its own purposes. This method has been used for centuries.
A second method for extracting essential oils is through expressing. This process generally only works with fruit rinds. Citrus oils can be extracted through intense compression used to squeeze out the oils of oranges, limes, lemons, and grapefruits. These oils are not technically essential oils, but are basically the same concept, referred to as expressed oils.
Enflourage is another means of extracting essential plant oils and is one of the oldest known methods. But it is a costly method and so is rarely used. Flower petals (like jasmine) are laid across glass coated with chassis (a layer of fat/oil). The volatile oil diffuses into the fat. Then the oil is extracted from this fat with alcohol. Finally, the alcohol is evaporated from the mix, leaving the essential oil in its pure form, called the absolute.
Solvent extraction is a method used in the perfume industry to get the highly aromatic essential oils from a plant or flower without the hassle of distillation. Using hexane, di-methylene-chloride, acetone, or other chemicals to extract the essential oils, solvent extraction is not a method for the use of essential oils in remedies, aromatherapy or other pure uses as the results are highly scented chemical compositions. This method is used in candles, shampoos, air fresheners, toothpaste, etc.
Percolation is a process France has mastered recently to extract essential oils. It is very similar to the distilling process. However, the equipment used is essentially upside-down. It produces an emulsion that may be difficult to separate out and is still being studied to perfect the method for large-scale use.
Other methods also include super critical fluid extraction, involving the use of highly pressurized carbon dioxide and the phytonic process, which uses non-CFCs (non-chlorofluorocarbons) to extract the oils. The former is expensive and not well studied, while the latter is a new method that is potentially harmful for the environment.
For purchasing essential oils of the highest quality, it is important to examine not only the methods of extraction, but also the growing, manufacturing, and storing processes. Distilling is recommended, but not all distillers are the same. Taking the time to investigate the quality of a companys procedures will ensure the best decision is made in the purchase of essential oils.