Steam distillation is the most efficient form of distillation and the most versatile. Before discussing the basic principles of essential oil production, it is important to understand that the essential oils people have in bottles or drums are not necessarily identical to what is present in the plant. With a few rare exceptions, it is wishful thinking to consider an essential oil to be “the soul” of the plant, and thus an exact replica of what is present in the plant. Only expressed oils that have not come in contact with heat or aerial oxidation may meet the conditions of a true plant essential oil. The chemical composition of distilled essential oils is not the same as that of the contents of the oil cells present in the plant or with the odor of plants growing in their natural environment.
Distillation produces essential oils and a byproduct called floral water, or hydrosol, hydrolate, herbal water and essential water, which are aqueous byproducts of distillation. They are colloidal suspensions (hydrosols) of essential oils as well as water-soluble components obtained by steam or hydrodistillation from plants and herbs. Distillates are used for flavorings, pharmaceuticals and cosmetics. Herbal distillates are produced in the same or similar methods as essential oils, but the appropriate term for the resulting product, essential water, is more descriptive and appropriate.
In the past, these essential waters were considered a byproduct of distillation. Today, they are considered co-products. The science of distillation is based on how different compounds vaporize at different temperatures. Unlike other extraction techniques based on the solubility of a compound in either oil or water, distillation will separate a multitude of compounds from the plant matter (although some will be lost in the water). The distillate will contain compounds that vaporize at or below the temperature of distillation. The actual chemical components of any distillate have not yet been fully identified, but distillates will contain some essential oil compounds as well as organic acids and other water-soluble plant compounds.
Compounds with a higher boiling point will remain behind and will include many of the water-soluble plant pigments and flavonoids. Herbal waters contain diluted essential oils. In addition to aromatic chemicals, these distillates also contain many more plant acids than pure essential oils, making them skin-friendly. The complete article may be found at :