Essential oils can be produced in a number of ways:
Steam distillation
Most essential oils are produced by steam distillation. It is best to use low or medium pressure steam distillation without the use of chemical solvents. Unfortunately, the distiller or producer is often more concerned with profit than proper treatment of the plants. High steam pressure and rapid distillation are more economical, but rarely produce an excellent and valuable product. Therefore, organic farmers, when producing organic essential oils, very carefully distill the plants using a slower - low-pressure steam distillation method.
Many plants require a longer distillation time to extract the full range of active compounds (especially the slow-boiling sesquiterpenes) from head to tail in the essential oil. These slow-boil, low-pressure methods produce a richer, more therapeutically effective essential oil.
Cold pressure
Most citrus essential oils are cold-pressed. Gently rubbing the skin of the fruit releases the oil contained in the small sebaceous glands in the skin.
Withdrawal
This is a common method used to produce oils from highly fragrant floral plants such as jasmine, tuberose, red champignon (in fact, many oils used in perfumery). Oils produced in this way are called absolutes. The plant material is thoroughly mixed with a solvent such as hexane, which dissolves the aromatics, as well as wax and other products. The solvent is then extracted, leaving behind a residue called concrete. Waxes and other unnecessary components are removed from the concrete with alcohol, leaving the oil behind.
CO2 extraction
CO2 extraction uses liquid carbon dioxide (compressed to about 300 atmospheres) to extract aromatics from plants. This method allows for little "cold" processing of the plants, as the oil can be extracted at temperatures around 30 degrees Celsius (90 degrees Fahrenheit). In most cases, the end result is a very subtle, rounded aroma (like jasmine CO2) that closely resembles the scent of the plant. Technically, CO2 extract is not an essential oil.
Hydrodiffusion
Hydrodiffusion is another variation of steam distillation. Steam is injected from the top of the still, not from the bottom. Distillation times are shorter, and this process often allows the vapors to penetrate the plant material better. Steam-distilled oils are sometimes a little more subtle.
Enfleurage / extraction
Enfleurage can be compared to some aspects of maceration, but it is done a little differently. Glass plates in frames (called chassis) are coated with highly purified and odorless vegetable or animal fat, on which the petals of the extracted plants are spread and pressed. Usually, the flowers are freshly picked before they are covered with a layer of fat. The petals are left in this fat mixture for a few days to allow the essence to diffuse into the mixture, after which the exhausted petals are removed and replaced with new petals. This process is repeated until the fat mixture is saturated with essence and must be repeated several times until saturation is achieved. When the mixture is saturated, the flowers are removed and the enfleurage pomade - the fat and scented oil - is washed with alcohol to separate the extract from the remaining fat, which is then used to make soap. The essential oils remain after the alcohol evaporates from the mixture. This method of extracting essential oils is labor-intensive and, of course, very expensive, and is now sometimes only used to extract tuberose and jasmine essential oils.