There are a variety of ways in which aromatic oils can be extracted from raw materials in the industry, and the method used depends on the characteristics of the material and the product that the perfumer desires. Manufacturers and houses may use variations of these methods to create their own specialties.
During steam distillation, the raw material is placed in a distillation flask with water, which is boiled. The heat releases the oils from the plant cells, and the oils are carried along by the steam. The vapors pass through and are condensed, in a tube surrounded by a tank of cool water known as a condenser, back into the liquid phase. The water containing essential oil is collected in a decantation vessel or an essencier where the two liquids can be separated as they are immiscible and have different densities. An essential oil is produced and the decanted water known as floral water retains scent. Two common types of floral water are orange flower water and rosewater.
The raw material is left to macerate to allow the fragrant oils to dissolve into the solvent, often volatile like hexane and ethyl alcohol. Once used up, the raw material is discarded and the remaining mixture is decanted then placed in a concentrator, where the solvent is evaporated, and may be partially distilled. A thick, waxy paste remains and is known as a concrete if derived from a fresh material such as a leaf or flower and retinoid if derived from a dry material like wood. The concrete or resinoid is treated with alcohol under cold temperatures to isolate the fragrant oils from the immiscible wax. Further evaporation of alcohol from the oil and alcohol mixture yields an absolute.
Solvent extraction is advantageous in that the aroma of the absolute is very close to that of plant.
Expression is only used for citrus fruits and the essential oils obtained are known as hesperidic oils. Traditionally, the oils were extracted by squeezing the citrus peel manually and were collected on sponges. Today, mechanical scrapers or crushers are used to express the oils from the peel. Water is present in the resulting product and is separated from the oils by centrifuge and decantation. The oils obtained are called essential oils.
Enfleurage is useful in extracting the scent from delicate flowers, for example rose and jasmine, by immersing the freshly picked flowers in a highly refined and odorless fat. When all the scent of the flowers have been absorbed by the fat, the flowers are replaced with new blooms and this process proceeds until the oil is saturated. The saturated oil is then called a ‘pomade’ that is washed with alcohol. This separates the fats from the oils, which remain in the alcohol. The oil-alcohol mixture is heated to evaporate the alcohol and give an oil known as ‘absolute de pommade’.
The Essence of Perfume by Roja Dove (2010), p.35-39
Perfume The Alchemy of Scent by Jean-Claude Ellena (2011), p. 20-22