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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 (poor tree!), and hardens on exposure to air. Various 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.