The distillation process involves heating the plant material until a vapour is formed, then cooling the vapour until it becomes liquid. In water distillation, the plant material is covered in water and heated in a vacuum-sealed container. This method is slower and sometimes inferior to steam distillation, because certain delicate components of essential oils are damaged by exposure to heat. The more efficient steam distillation uses steam under pressure to swiftly extract the essential oil. It is the most common method of extraction. Plant material is heated by steam in a still, and the volatile parts present in the plant evaporate into the steam. These vapours are carried along a closed outlet, and are cooled and condensed by being passed through a cold-water jacket. The resulting water is collected in a flask and the essential oil floats on the surface. Floral water is a by-product from this process. Oils that are extracted by this method: Chamomile, Rose Otto, Neroli, Lemongrass, Peppermint, Geranium, Immortelle, etc
Using this extraction method, the plant material is placed in a drum with a volatile solvent such as petroleum ether, hexane and benzene as a mean for capturing the essences of certain plant and resins. The solution is filtered off and concentrated by distillation, leaving behind either a “concrete”, a combination of wax and essential oil, or a “resinoid”, a substance containing resin. A second process of solvent extraction using pure alcohol recovers most of the oil. The alcohol is then evaporated, leaving a solution called “absolute”. Oils that are extracted by this method: Jasmine, White & Pink Lotus, Tuberose, Champaca, Frangipani, etc.
The oils of citrus fruits such as Lime, Bergamot and Lemon are much easier to obtain. The essence is found in such profusion that it sprays the surrounding air when the fruit is peeled. The highest quality citrus essences are captured by a simple process known as expression. Although this was once carried out by hand, machines using centrifugal force are now used instead. Since no heat is employed in this process, the aroma and chemical structure of expressed oils is almost identical to that contained within the skin of the fruit. Unlike distilled oils, expressed essences also contain non-volatile substances such as waxes. The drawback with expressed oils is their relatively short shelf-life. Even though producers usually add tiny amount of preservative at source, the oils will still deteriorate within six to nine months, whereas most distilled essences will keep for upwards of two years. Oils that are extracted by this method: Lemon, Lime, Orange, Kaffir Lime
This process was hailed as revolutionary when it was introduced. Although a potentially excellent method of extraction, producing oils whose aromas are closer to those of the living plant, the apparatus required for this operation is not only massive, but also extremely costly. The extraction method uses carbon dioxide gas at very high pressure to dissolve essential oil from a wide range of plant material. When the pressure is allowed to fall, the oils form a mist and can be collected. The resultant oils are free of the potentially harmful residues associated with solvent extraction, but there are those who argue that carbon dioxide is an acidic gas and therefore detrimental to the chemical structure of essential oils.
This phytonic process was recently developed by British microbiologist Dr. Peter Wilde in collaboration with the multinational chemical company. Proponents of phytonics technology believe that it heralds the biggest breakthrough in aromatic oil extraction since the discovery of distillation. The process has been developed around a family of new solvents collectively known as phytosols, whose unique character ensures that the aromatic oils of plants can be captured at room temperature. This means that the exceptionally fragile, heat-sensitive components of an aromatic oil are not lost, or radically altered, in the extraction process.