Review: EXTRACTION OF HERBAL AROMA OILS FROM SOLID SURFACE

Fragrance extraction refers to the extraction of aromatic compounds from raw materials, using methods such as distillation, solvent extraction, expression or enfleurage. The results of the extracts are either essential oils, absolutes, concretes or butters, depending on the amount of waxes in the extracted product. To a certain extent, all of these techniques tend to distort the odour of the aromatic compounds obtained from the raw materials. Heat, chemical solvents or exposure to oxygen in the extraction process denature the aromatic compounds, either changing their odour character or rendering them odourless. This technique is very costly and is rarely used today. It reached its peak in 1860 and made the reputation of Grasse. It is a labour-intensive process that yields the highest quality of absolutes because it does not involve heat. Heat always alters the fragrance. It is used on delicate flowers that cannot stand up to the high heat and that continue to release essential oils after they have been picked. Examples of these flowers are Jasmine, Violet, Tuberose and Rose. Enfleurage goes back thousands of years to the ancient Egyptians. It works on the principle that fats absorb smells. Petals or other fragrant parts of a plant are steeped in fat or non-evaporating oil which will absorb their fragrance. A mixture of pork, lard and beef suet is smeared on to a glass plate in a wooden frame called a chassis. The flowers are placed on the fat and left to release their oils for several days. This process was repeated several times with fresh flower heads until the fat was totally absorbed with essential oil, the resultant substance being known as 'pomade', the oil was then retrieved from the fat by dissolving in an alcoholic solvent. This is mechanically mixed with alcohol for up to one week, and is chilled to 68°F. The essential oils dissolve in the alcohol and the fat does not. The mixture is chilled and filtered several times to remove all the fat. The alcohol is then evaporated to leave the pure absolute. Sometimes enfleurage is now carried out with cloth soaked in olive oil or liquid paraffin, which is laid over the frames instead of fat, the resultant perfumed oil being then known as 'huile antique'.