Читать книгу Encyclopedia of Essential Oils: The complete guide to the use of aromatic oils in aromatherapy, herbalism, health and well-being. - Julia Lawless - Страница 39

An absolute is obtained from the concrete by a second process of solvent extraction, using pure alcohol (ethanol) in which the unwanted wax is only slightly soluble. An absolute is usually subjected to repeated treatment with alcohol; even so, as is the case with orange flower absolute, a small proportion of the wax remains. Absolutes can be further processed by molecular distillation which removes every last trace of non-volatile matter. The alcohol is recovered by evaporation which requires a gentle vacuum towards the end of the process. Some absolutes, however, will still retain traces of ethyl alcohol, at about 2 per cent or less, and are not recommended for therapeutic work because of these impurities.

Absolutes are usually highly concentrated viscous liquids, but they can in some cases be solid or semi-solid (clary sage absolute). In recent years, much research has been devoted to the extraction of essential oils and aromatic materials using liquid carbon dioxide; oils produced in this manner are of excellent odour quality and are entirely free of unwanted solvent residues or non-volatile matter.