Читать книгу Aromatherapy Workbook - Shirley Price - Страница 24

This method of extraction is used exclusively with citrus fruits, where the essential oil, located in little sacs just under the surface of the rind, simply needs to be pressed out. You can do this for yourself on a small scale: squeeze a succulent section of orange peel within an inch of a candle flame or lighted match and the tiny droplets of essential oil will ignite like baby fireworks. This shows not only the volatility of essential oils, but also that one needs to keep them away from a naked flame, as they are highly inflammable.

Expression is usually carried out by a factory producing fruit juice, thus maximizing the profit from the whole fruit. Most essential oil of orange comes from the USA, where millions of oranges are processed for their juice. The best essential oil does not come from there, as in order to maximize the crop, the trees and fruit are sprayed with chemicals, and these toxins reach the essential oil glands. This would not be so important if citrus fruits were distilled, as most pesticides and fertilizers, being composed of larger molecules, do not come through in the distillation process. Nevertheless, as expressed oil is taken directly from the fresh peel without heat, it is best that citrus oils for therapeutic use be obtained from organically or naturally grown produce.

FIGURE 2.2: Hydrodiffusion

Cold-pressed citrus oils are special, in that they are acknowledged to be exactly the same composition as when in the plant itself. In many juice/ essential oil factories the peel is steam distilled after expression, which releases even more oil (though of a poorer quality). Sadly for the aromatherapist, this is often added to the expressed essential oil to ‘bulk’ it, so care is needed when purchasing.

Although the oil was extracted by hand in the past (and collected in sponges), the size of the industry nowadays necessitates expression by machinery, when it is known as ‘scarification’. In expression, both volatile and large molecules (such as waxes and other substances) are contained in the finished product, in contrast to distillation where only the tiny volatile molecules are collected.

The storage life of expressed oils is shorter than that of distilled oils, and although they have approximately 0.002 per cent antioxidant added to them, they are best kept in a cool, dark place (many people choose the refrigerator). In too cold an environment the dissolved waxes are precipitated, making the oil cloudy; this does not affect the therapeutic qualities (the wax has no therapeutic effect) so should this happen, simply strain your oil if you prefer it clear – warming the oil will not work, as the waxes will not go back into solution.