Some vendors offer several different kinds of one essential oil. These oils are listed as chemotypes. What are they and how do their aromas differ from standard oil?
The energies and effects of light, soil, temperature, moisture and climate influence the life processes of plants and the formation of essential oils. Differences in plants arise as a result of isolation, mutation and evolution in the face of continued climatic change or stress. This process can eventually lead to the development of new species, but subtle yet permanent changes may arise even when the various plant forms remain botanically identical. When conditions cause the plants to permanently produce variations in the chemical makeup of their essential oils, these plants are known as chemotypes. An essential oil chemotype is not created in a laboratory by adding or extracting certain components of an oil. For instance, a camphor chemotype rosemary oil is extracted from a rosemary plant with a natural preponderance of camphor. On the other hand, a pure and natural rosemary oil with a decreased camphor note would be extracted from a different chemotype of rosemary known as verbenon. Verbenon rosemary has more of the balsamic-piney aroma typical of a fresh plant than the penetrating, refreshing notes more typical of the well known camphor chemotype.
Another plant that displays a wide variation of chemotypes is basil. These differences are readily apparent to herb gardeners, who may grow varieties that include licorice, lemon and cinnamon scented plants. The two types of basil essential oils of greatest importance to aromatherapy are sweet basil oil and Reunion basil oil. The European type, or pure sweet basil oil, is distilled from a strain of basil with an exceptionally high proportion of the terpene alcohol constituent known as linalool. Pure linalool has a fine, delightfully sweet aroma. Its aromatic properties are apparent in a variety of essential oils including rosewood and lavender. The finest European type basil oils are distilled from isolated strains of basil with a high percentage of linalool. These oils are quite hard to come by and are highly priced. The Reunion type basil oil is distilled from a strain of basil growing on Reunion and the Comoro Islands off the east coast of Africa. The Reunion chemotype essential oil has a more woody-camphoraceous aroma due to the absence of linalool and the presence of methylchavicol and camphor. Most commercially available basil oil will present an aroma that seems to be somewhere between the extremes of the European and Reunion type oils -- woody, anisic or licorice-like, sweet and occasionally camphoraceous.
The commercially important lavandin oils come in a variety of chemotypes, most of which have been created through selective breeding. The lavandin oils are distilled from a hybridized plant known as Lavendula hybrida -- a cross between true lavender (Lavendula officianalis) and spike lavender (Lavendula latifolia). The plants are exceptionally robust and vigorous, making production easier and more profitable. The different chemotypes of lavandin have less to do with climatic influences than with the varying ratios of inherited traits from the two parent plants. In general they are lower in the sweet-floral notes such as linalool and linalyl acetate, and higher in the herbaceous camphoraceous notes such as cineole and camphor. Lavandin is used to scent soaps, detergents and cosmetic preparations.
Other plants that yield essential oils which demonstrate a variety of chemotypes include: thyme, geranium, eucalyptus, tea tree, myrtle and spike lavender. As time goes by, more chemotypes will be discovered and isolated from wild-growing plant populations, as well as from plant species produced through selective breeding in captivity. Users of essential oils can use chemotypes to create interesting variations in personal fragrances, cosmetics and aromatherapy.