The essential oils are derived from many plants and particularly the higher plants which have evolved essential oils partly as a defence against insects and disease.
The term Essential oil is any of a large class of volatile odoriferous oils of botanical origin that impart to plants odor and often other characteristic properties, that are obtained from various parts of the plant (as flowers, leaves, roots, fruits, berries, seeds, food parts, bark, etc.) by steam and/or water distillation, expression or extraction, that are mixtures of compounds (as terpenoids, aldehydes, alcohols, esters, etc.), and that are used often in the form of essences in cosmetics, flavorings, fragrances, perfumes, aromatherapy and pharmaceutical preparations
Rose Otto, Frankincense and Myrhh are obtained by hydrodistillation
Most essential oils are obtained by steam distillation of the plant matter
Vegetable oils and essential oils obtained from fruit rinds like lemon are crushed or pressed.
Concretes
A first step in the production of absolutes. The concretes are obtained by different processes. For example, the flowers, leaves, roots etc. are subjected to extraction by solvents which dissolve the waxes and essential oil containing the odorous principles from the flowers, leaves, roots etc. The solvents are then eliminated by evaporation under reduced pressure so that the heat does not effect the product so obtained, which is called an concrete or simply a concrete. The concrete of the flowers, leaves, roots etc. so treated has the appearance of a more or less solid wax. It is insoluble in water and virtually insoluble in alcohol.
Absolutes
The Absolute is obtained by extracting the concretes with solvent, usually hexane, then eliminating the solvent at reduced pressure. The product so obtained often has the consistency of honey and may not be entirely soluble in alcohol. There is some hexane left behind, which should be less than 1 Part Per Million. There are other type of extraction methods in use today that involve the use of butane gas (boiling point -0.5øC). the absolute so obtained tends to be light in color and true to type, but in some cases it may not be entirely soluble in alcohol.
Pomades
A very old process is that of the "pomades". There were two ways of carrying it out:
(1) The process of maceration in the hot state, which consisted of melting an odorless fat and allowing the flowers to be macerated in it, the fat or oil being kept at a medium temperature for the fat to be liquid, without excessive heating. The fat absorbs the perfume. In the past, forms of alcoholate were prepared, by extracting these pomades with alcohol in the cold state. Pomade washings (lavage de pommade) were obtained, which showed their concentration according to the number they bore. Then extractions of these pomades with alcohol were carried out to obtain concentrated solutions and the alcohol was evaporated, in order to produce the absolute essential oils ex pomade.
(2) The process of maceration in the cold state, or enfleurage. In this process, fat or oil is also used. It involves coating the glass plates of glazed wooden frames with a fat or oil. Inside these frames (termed cadre or chassis), on the part coated with fat, are placed the flowers. The frames are stacked on one another so as to obtain a hermetic seal and they are allowed to stand for 24 hours, so that the effluvia liberated dissolve in the fat or oil. The flowers that have given up their perfume are removed and replaced by fresh ones. This operation is repeated until the fat is saturated with perfume. The perfumed fats are treated with alcohol, and by increasing these extraction operations, followed by chilling and filtration, an alcoholic solution is obtained, which is subsequently concentrated by evaporation to yield the absolute enfleurage essential oil.
Essentia
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