The Life Cycle Of An Essential Oil
Only certain plants contain essential oils, and they are known as aromatic plants. The oil is formed in the secretory cells; very small structures in the leaves, flowers, or other parts of the plant.
Both the quantity and the composition (mix of ingredients) of an essential oil are constantly changing within the plant – with time of day, time of year, maturity of plant, weather, and many other factors. Consequently there are optimum seasons, and times of day, to harvest a plant for its essential oil.
Harvesting can be done by hand, or mechanically. Some plants, such as rose flowers, can only be picked by hand, hence one of the reasons rose is one of the most expensive oils, but other herbs such as lavender are usually cut mechanically.
Oil extraction is carried out as soon as possible after harvesting, to avoid and minimalize evaporation of the essential oil.
Extraction may be done by cold pressing (citrus fruit oils), steam or water distillation, or by use of a solvent.
The essential oil is then stored and transported in metal drums. It may then be blended with other oils and fragrant materials to make a flavour or fragrance, compounded into a medicine, or sold in its own right for aromatherapy.
Robert Tisserand, one of the worlds leading experts in Aromatherapy explains how essential oils work:
"Once applied to the body, whether by inhalation, application to the skin or other means, an essential oil enters the bloodstream. The essential oil is metabolised – chemically changed – quite rapidly, but during this period a multitude of therapeutic effects are possible. Some of these are due to constituents before they are metabolized, and some are due to metabolites – new chemicals formed in the body.
The essential oil constituents often work synergistically, though they don't always do so. They act in a variety of ways, such as interacting with receptor sites on the surface of cells. Menthol, in peppermint oil, for example, lowers blood pressure marginally by altering the way calcium is exchanged at the surface of blood vessel cells.
Another way in which essential oils operate is by interacting with the cells of the 'olfactory epithelium' – a membrane inside and at the very top of the nose – after inhalation. The interaction of fragrant molecules and olfactory membrane initiates a nerve signal that may quickly trigger various parts of the brain, invoking a memory, a feeling, or simply the perception of a fragrance."