Extraction of essential oils
Steam distillation, solvent extraction, maceration, defleurage, enfleurage
Since any part of a plant may produce essential oils, the method of extraction depends upon the site and accessibility of the essence in each particular case. The oils are produced by special minute cells or glands and are released naturally by the plant in small amounts over a prolonged period of time when needed. In order to harvest the oils in appreciable amounts, it is usually necessary to collect a large quantity of the part of the plant needed and to subject the material to a process that causes the oil glands to burst. One of the most common methods is steam distillation.
The plant material is paced tightly into a press or still and steamed at a high temperature. This causes the oil glands to burst and the essential oil vaporizes into the steam. This is then cooled to separate the oil from the water. Sometimes water is used for distillation rather than steam. Another method involved dissolving the plant material in a solvent or alcohol and is called solvent extraction. This involves placing the material in a centrifuge, which rotates at high speed, and then extracting the essential oils by means of a low temperature distillation process. Substances obtained in this way may be called resins or absolutes.
A further method is called maceration in which the plant is soaked in hot oil. The plant cells collapse and release their essential oils, and the whole mixture is then separated and purified by a process called defleurage. If fat is used instead of oil, the process is called enfleurage. These methods produce a purer oil that is usually more expensive than one obtained by distillation. The essential oils used in aromatherapy tend to be costly as vast quantities of plant material are required to produce them and the methods used are complex and costly.
Storage and use of essential oils
Essential oils are highly concentrated, volatile and aromatic. They readily evaporate and change and deteriorate if exposed to light, heat and air. Hence pure oils need to be stored carefully in brown glass bottles at a moderate temperature away from direct light. They can be stored for one or two years in this way. For most purposes in aromatherapy, essential oils are used in a dilute form, being added either to water or to another oil, called the base or carrier. The base is often a vegetable oil such a olive or safflower, which both have nutrient and beneficial properties. An essential / carrier oil mixture has a short useful life of two or three months and so they are usually mixed at the time of use and in small amounts.
Blending essential oils
Essences can be blended to treat specific ailments, and some aromatherapy books contain precise recipes for blends. When two or more essential oils are working together in harmony, this is known as a synergistic blend. Obviously, it takes many years of experience to know which combinations of plant essences will work most effectively together, but as a rough guide, oils extracted from plants of the same botanical family will usually blend and work well together, although it is by no means necessary to stick rigidly to this rule as other combinations may be just as successful. Really, a number of factors need to be taken into account when preparing a blend of oils for a patient, such as the nature of his / her compliant, his personality or frame of mind. For home use, it is not usually beneficial to blend more than three oils for any one preparation.