Essential oils are produced in the cells of aromatic plants and are held in specialized glands. They are released from the plant and collected (concentrated) most often through steam distillation (and sometimes hydro or water distillation or a combination thereof). Distillation is a method of separating components based on differences in volatile constituents in a heated mixture. Steam distillation involves bubbling steam through the plant material. The temperature of steam is easy to control, making it ideal for heat-sensitive essential oils. The essential oils contained in plants are immiscible in water and have a higher boiling point, allowing the essential oil to vaporize at a lower temperature than it normally would on its own.
Concretes and Absolutes are highly concentrated aromatic materials extracted from plants. The multi-step process includes first extracting the aromatic oil from the plant material with a solvent such as hexane. After the hexane is removed what is left behind is a waxy substance called a concrete. This semi-solid to solid highly fragrant material contains a large amount of pigments and waxes. Due to their waxy texture, concretes are perfect for making solid perfumes. They have a somewhat delicate, yet long lasting aroma and are soluble in both carrier oil and alcohol. From the concrete the aromatic oils are then extracted and separated from most of the plant waxes and non-aromatic material with ethyl alcohol. After the ethyl alcohol is removed, the remaining substance is called an absolute. An absolute is the most concentrated form of natural fragrance, with an aroma close to the plant from which it came, and is highly regarded in natural perfumery.
In cold enfleurage, a large framed plate of glass, called a chassis, is smeared with a layer of fat then the botanical matter, usually petals or whole flowers, is then placed on the fat and its scent is allowed to diffuse into the fat over the course of 1-3 days. The process is then repeated by replacing the spent botanicals with fresh ones until the fat has reached a desired degree of fragrance saturation. This procedure was developed in southern France in the 18th century for the production of high-grade concentrates.