Essential oils are used in perfumes, in aromatherapy, in creams and lotions and for many other purposes where pleasant aromas are needed. Several methods are used to extract essential oils from flowers and other plant material. Essential oil makes up only a very small percentage of the plant or flower so a large amount of plant material is needed to produce a small amount of oil. More than a hundred pounds may be needed to produce an ounce of oil. Some flowers are also too delicate to use the easier methods and more time consuming and expensive methods must used. Essential oils can be expensive but they are very concentrated. Most recipes only require a few drops so a small bottle will last for a long time.
Steam distillation is used for the majority of Essential Oils production. Pressurised steam is passed through flowers or other plant material spread on screens inside a still. The oils are absorbed by the steam which is then passed into another chamber and cooled. On condensing the oil floats on the top of the water and is skimmed off. The water remaining is not wasted as it contains small amounts of the oil and can be used for toners and facial mists. As it is not as concentrated as the essential oils floral water can be used by people who are sensitive to essential oils.
For flowers or plants too delicate to use steam extraction solvent extraction is often used. A solvent, usually hexane, is repeatedly passed over the plant material on mesh trays. The oils, along with other soluble substances, are absorbed by the solvent which is then filtered and the resulting solution distilled under low pressure to remove the solvent. The material left, called a concrete, is a waxy solid containing the essential oils and waxes and pigments from the plants. Further processing is then carried out to extract the oils and waxes from the concrete. The concrete itself can also be used as a perfume and the waxes are used in lotions, creams and in candle making.
For flowers or plants that have very low levels of essential oils, jasmine for instance, a different method must be used. Flowers are placed into odourless vegetable oil and left for a few days before being replaced by fresh material. Fresh flowers are repeatedly placed in the vegetable oil until it is saturated with the oil from the flowers. Alcohol is then used to extract the essential oil from the vegetable oil. When the alcohol is evaporated the pure essential oil is left. This process takes a long time and a large amount of plant material and the resulting oil is very expensive.
For citrus oils, where the oil is extracted from the fruit rather than the flowers cold pressing is used. This entails rolling the fruit between spiked projections which pierce the peel and then squeezing the fruit to extract the juices which contain the oil. The resulting juice is then centrifuged to separate the oil.
Carbon Dioxide Extraction
In this method carbon dioxide is used to extract the oil. A high pressure is achieved by pumping the gas into a chamber containing the plant material. As the pressure increases the gas liquifies and acts as a solvent. The essential oils are extracted into the liquified carbon dioxide which is then passed into another chamber where the pressure is released. The carbon dioxide vapourises leaving behind the essential oil.
No residues are left behind and the extract is very pure with a clean and fresh aroma. As the temperature used is much lower than that used for steam distillation, oil can be extracted from delicate flowers that are destroyed by steam distillation.
Steam Diffusion Extraction
This method is similar to steam extraction but the steam is introduced into a chamber with the plant material at atmospheric pressure rather than at high pressure. It is a gentler method and can be used for more delicate flowers and plants.