The oil is taken out of the plant by distillation, expression or extraction.
In distillation, steam vaporizes the lighter parts of the plant material (phytomolecules) , creating two byproducts—the essential oil and a hydrosol. The hydrosol may be commercially useful itself. For example, distilling rose petals yields rose oil (an essential oil) and rose water (a hydrosol with cosmetic and culinary uses.)
Expression is used to separate essential oils from citrus fruits. Here the peel is grated to obtain the essential oil. No heat is involved so essential oils derived from citrus fruits smell similar to the original fruits; sometimes in the first method (distillation), the heat causes the essential oil to smell differently from the original plant.
A newer separation method is supercritical CO2 extraction (SCE). Carbon dioxide is added and removed to derive an extract which is closer to the original plant material than that produced by the other methods. In other words, SCE preserves “a wider range of the chemical molecules” found in the original material. Therefore, an essential oil of the same original plants will be different if it is acquired by distillation than by SCE. This difference may mean a distilled essential oil has therapeutic properties independent of those held by a SCE essential oil. The essential oil produced by SCE is often called a CO2. As with expression (and unlike steam distillation), no heat is used in SCE, preventing any possible temperature damage to the essential oil.
Extraction can also be done with chemical solvents. Although the solvent is removed, trace elements may remain, which may alter the therapeutic effect of the resulting oil, which is called an absolute. Absolutes are held to be more concentrated than essential oils.
- Essential oils are derived from plant, herb or tree parts.
- Essential oils are taken out by distillation, expression or extraction.
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