form the aromatic water. Because of the presence of these other molecules, genuine waters have a different aroma from the essential oil of the same name.
The water from plants with a high yield of essential oil is normally discarded – directed into the nearby stream (large stills are always located beside a stream or river). However, with low-yield oils like melissa, rose and neroli, producers cannot afford to lose a single drop of the precious essential oil, so a special method called ‘cohobation’ is used, requiring a highly technical still and an experienced distiller. The basic process is as described above, except that, instead of using fresh water for each new plant load, the same water is piped back into the system, and used over and over again. Eventually, this water becomes saturated with the water-soluble elements from the plant (and water-soluble essential oil components). At this stage, every particle of volatile oil condenses and is collected at the end of the process to make a complete oil.
This saturated water is very concentrated and this strength is good for transport, as it saves on freight costs: it needs to be diluted with pure water to be comparable in strength with other plant waters. Lavender, clary and other waters from normal distillation are not as cheap as one would think (considering they are thrown away unless specifically ordered in advance), because of the cost of packaging and transport.
Before Avicenna’s improvement to distillation and before cohobation was thought of, rose and neroli flowers were distilled simply for the water – the amount of essential oil obtained was negligible. In Tunisia, our friend Manoubi’s mother, like many Arab women today, has her own tiny still, in which she makes orange flower water for her own medicinal and culinary use.
Unfortunately, unless one has a good connection in the country of origin (which, fortunately, we do), it is as difficult to buy untampered-with aromatic waters as it is to buy untampered-with essential oils (almost all rose water available in pharmacies is made with synthetic substitutes).
Aromatic waters can be made from plants which have no essential oil, by using diffusion.
Carbon Dioxide Extraction
This is a fairly new method of extracting essential oils, introduced at the beginning of the 1980s, utilizing compressed carbon dioxide. The technology calls for very expensive, complicated equipment (initially three or four million pounds’ worth), which utilizes carbon dioxide at very high pressures and extremely low temperatures. With this method, more top notes, fewer terpenes, a higher proportion of esters (see chapter 3), plus larger molecules, are obtained. The aroma of the resultant oil is more like the essential oil in the plant, as many terpenes in a distilled oil seem to form during the distillation process, which also breaks down some of the acetates (esters) in the plant material.
Carbon dioxide (CO2) extracted essential oils are pure and stable and have no residue of CO2 left in them. However, the therapeutic possibilities need to be verified for each oil on account of their different compositions and until there has been some research on this, it may be wise not to use them yet in aromatherapy.
At the moment the price is high; perhaps after a number of years, when the initial cost of the equipment has come down, the prices will be lower.
Hydro-Diffusion or Percolation
Percolation is even newer than CO2 extraction and in 1991 we visited a unit in France. It was extremely interesting; most of the resultant oil had an aroma nearer to the plant than a distilled oil. The equipment, unlike that for CO2 extraction, is very simple and the process quicker than distillation, the plant being in contact with the steam for a much shorter time.
This process works like a coffee percolator. The steam passes through the plant material from top to bottom of the container, which has a grid to hold the plant material. The oil and condensed steam is collected in a vessel in the same way as distillation. The colour of oils I have seen is much richer than that of distilled oils and time and tests alone will, as with the CO2 method, reveal their true value in aromatherapy – it is certainly exciting! Percolation is not suitable for all oils; there are still a few practical difficulties to overcome (sometimes an emulsion is produced), but I am tempted to do a research project on one or two myself!
Expression
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.
Solvent Extraction
Absolutes and resinoids are obtained by solvent extraction and are not classed as essential oils. They are highly concentrated perfume materials, containing those plant molecules which are soluble in the solvents used to produce them.
Resinoids
Resins are the solid or semi-solid substances exuded from the bark of trees or bushes when wounded (cut, as in a rubber tree). The gum-like substance produced does not exist in the tree beforehand but is produced pathologically solely as a result of the incision
