solvents can be used to extract the aromatic molecules from the resin, the most frequently used being hydrocarbons (e.g. benzene, hexane or alcohols – each extracting different molecules). The solvents are filtered off and afterwards removed by distillation to leave either resinoids (from hydrocarbon solvents) or absolute resins (from alcohol solvents).5
Concretes
The extraction of concretes is similar to that of resinoids (hydrocarbons are used as solvents). For concretes however, plant material (leaves, flowers, roots, etc.) is used instead of a resin – this is the main difference. Most concretes are solid, wax-like substances and are much used in food flavourings.
Absolutes
An absolute is prepared from a concrete, by adding an alcohol to extract the aromatic (alcohol-soluble) molecules. The alcohol is then evaporated off gently under vacuum, leaving the absolute, a thickish, coloured liquid. The total process is much more complicated than I have made it sound!
Absolutes and resins are much used in the perfumery world, and although they can be useful in some applications of aromatherapy, it must be appreciated that they always retain a small percentage of the solvents used in their production. Some solvents may cause a substance sensitivity (see chapter 6) on certain skins, depending on the quality and quantity of the retained solvent. Adulteration is also a factor in this respect. Jasmine absolute, a favourite aroma for many people and possibly the most important fragrance in the perfume industry (there is no essential oil of jasmine available), is extremely vulnerable to adulteration6 and available at a wide range of prices – reflecting the quality.
Enfleurage
Pommades were obtained from the enfleurage process used long ago (replaced by concretes), when petals or leaves were laid on trays of animal fat for many days, being replaced regularly until the fat used as a solvent was saturated with the plant extracts.
Adulteration
The perfume industry is far and away the biggest user of essential oils, followed by the food industry. These industries have to obtain an oil having the same chemical formula (therefore giving the same aroma and flavour) time after time, year after year. It has always been accepted in perfume and flavouring trades that essential oils are standardized and not always 100 per cent true, nor are they always from a named botanical species – they have no need to be. They are being used not to influence the health of the body, but as fragrances or flavourings – a totally different kettle of fish! When aromatherapy arrived on the scene, it was an incredibly small part of an essential oil trader’s business – litres instead of tonnes. The trader could not be expected to undertake the uneconomic supply of special non-standardized or untreated oils for such a small section of his business. This is largely true today and unfortunately there are still suppliers of essential oils to aromatherapists who get their oils from such sources.
It will help to illustrate why it is important for the perfume and flavour industries to alter the original, natural composition of an essential oil if I make a comparison with wine. It is well known that there are good and bad years for wine; the same vineyard making its wine from the same vines each year will produce differences in aroma and taste from year to year. Weather and environment play their part in producing these changes, as they do with essential oil plants, altering the chemical formula of the oil produced. Furthermore, the same plant grown in another part of the world will yield a different oil again. Thus, the perfumer making up a well-known fragrance from a recipe including essential oils experiences a difficulty. For him, essential oils must be standardized, otherwise the end product would neither have the expected aroma, nor be acceptable: it is a question of adjusting (adulterating) the essential oils to achieve a legitimate aim.
Terpenes, a dominant feature in most essential oils, are sometimes removed to concentrate the remaining, more desirable constituents. The resulting compounds are known as folded or terpeneless oils, the terpenes often being used to adulterate another oil (see below).
Essential oils are also adulterated for commercial reasons – perhaps in an unethical way when operating in the field of aromatherapy. Before we bought our essential oils direct from the growers we were often asked, when ordering, ‘How much do you want to pay?’ In those days we did not realize what a complex business it was to buy essential oils, but we knew enough not to like being asked how much we wanted to pay, rather than being told the straightforward cost of the genuine oil!
What is Adulteration?
Adulteration, cutting, standardization, stretching, ennobling, sophistication – call it what you will, these terms, together with rectification (see below) mean that an essential oil has been altered in some way since leaving the still. Some of these processes are simple; some are quite complex, requiring sophisticated equipment. All these terms apply when the producer (or an intermediate further down the supply line) adds something to his essential oil to ‘stretch’ or standardize it.
Adulteration of essential oils can be carried out in a number of ways. The adulterant used may be:
1 an alcohol (to the inexperienced, the aroma is not noticeably different from the pure oil).
2 an isolate obtained from other essential oils (e.g. lemon or orange terpenes, which are available in huge quantities at extremely low cost).
3 a different, cheaper essential oil (and the claim may still be made in this (and no. 2) that the product is still a natural essential oil!)
4 a synthetic product, such as DPG (dipropylene glycol, which is colourless and odourless and is commonly added to bulk up lavender oil) or PEA (phenyl ethyl alcohol, a natural constituent of rose otto, which may be used to augment that oil).
5 an alternative, cheaper oil, somewhat similar, and substituted in toto (lavandin is often sold under the name of lavender, thus quadrupling the traders’ profit – see chapter 5).
These methods are more or less accepted in the world of perfumery; indeed, I have been told by some that an essential oil may be regarded as pure if the oil contains 51 per cent of the original material; it is a fact that an essential oil is occasionally referred to as ‘the soup’ by some perfumers. This, however, should not be tolerated in the world of therapeutics, where to have a true to its name, untampered-with essential oil is of paramount importance.
I quote from the Haarmann & Reimer Book of Perfume7
‘…bad harvests, political conflicts, exhaustion of the soil or transportation difficulties are imponderables which make it impossible for the perfumer to rely on Nature’s raw materials. Against that background, synthetic fragrance substances appear as economically indispensable substitutes for Nature’s originals.’ [my italics]
Fractionation
Here, re-distillation is carried out at low pressure in order to isolate the various chemical constituents, resulting in a terpeneless or a folded oil.
1. Terpeneless Essential Oils
These are essential
