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 36

An essential oil is extracted from the plant material by two main methods: by simple expression or pressure, as is the case with most of the citrus oils including lemon and bergamot, or by steam, water or dry distillation. The majority of oils such as lavender, myrrh, sandalwood and cinnamon are produced by steam distillation. This process only isolates the volatile and water-insoluble parts of a plant – any other (often valuable) constituents, such as tannins, mucilage and bitters, are consequently excluded from the essential oil. Sometimes the resulting oil is redistilled or rectified to get rid of any remaining non-volatile matter; some essential oils are redistilled at different temperatures to obtain certain constituents and exclude others – as with camphor which is split into three fractions, white, yellow and brown.

The process of steam distillation as it is practised today

Essential oils are usually liquid, but can also be solid (orris) or semi-solid according to temperature (rose). They dissolve in pure alcohol, fats and oils but not in water and, unlike the so-called ‘fixed’ plant oils (such as olive oil), they evaporate when exposed to air leaving no oily residue behind.