Hydrosols: Aromatherapy's "Other Half"

Essential Oil and Hydrosol Distillation

Most essential oils are obtained by steam distillation, where steam is passed through the botanical material from a plant, releasing the volatile aromatic compounds when the heat causes the plant’s cell walls to burst. The essential oil molecules and steam are then cooled, resulting in condensation. Since oil and water are not mutually soluble, the non-water soluble fraction (the essential oil) is separated from the water-soluble fraction (the hydrosol or hydrolate/hydrolat) by pouring off the top layer or draining the bottom layer through a spigot in the collection vessel.

I first learned about hydrosols after I received Suzanne Catty's book, Hydrosols: The Next Aromatherapy, as a gift. It describes the properties of hydrosols vs. the properties of essential oils, includes extensive information about producing and storing hydrosols, and presents monographs (profiles) of around 70 hydrosols.

Hydrosols Are More Than Just a Coproduct

Though aromatherapy most often refers to use of the essential oil product of the distillation, the hydrosol coproduct often contains therapeutic molecules as well, depending on the plant. Hydrosols do have therapeutic value, though this branch of aromatherapy is less widely known.

Note that hydrosols are obtained only through distillation, as expression and solvent extraction do not produce a water fraction coproduct. Hydrosols are often confused with "floral waters," but they are not the same. Floral waters are usually prepared by infusing water with an essential oil or with a synthetic fragrance, whereas hydrosols are the natural, direct aqueous product of distillation.

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Hydrosols have interesting properties in themselves, and while their therapeutic actions sometimes overlap with their essential oil counterparts, the hydrosol can have quite different effects from its corresponding essential oil. A hydrosol's aroma may be similar to the corresponding essential oil, but in some cases can be quite different.

Special Considerations for Handling and Storing Hydrosols

Because hydrosols are aqueous (water-based), they are much more prone to spoilage from bacterial or mold growth than are essential oils. Because of this, hydrosols are often stored with a small amount of ethanol (ethyl alcohol) which helps inhibit bacterial growth. Hydrosols must be handled carefully, stored in sterile glass bottles, and kept in refrigeration. When using hydrosols, it is imperative to handle the containers in such a way that introduces as little contamination as possible.

However, with proper handling and storage, well-stored hydrosols will keep for several months in many cases. I have managed to keep pure, unpreserved hydrosols for six months without mold growth, by keeping them refrigerated and keeping the containers tightly closed. It is best to order hydrosols in smaller quantities and use them more quickly, than to buy large bottles and try to store them for extended periods.

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How Are Hydrosols Used?

In many ways, hydrosols are more "gentle" than essential oils. Hydrosols are many times less concentrated than essential oils, and where direct application of many essential oils will cause irritation, in many cases hydrosols can be used undiluted and much more liberally. In addition to their therapeutic benefits, hydrosols can be used in body splashes and sprays, facial masks, and they make excellent facial toners. Suzanne Catty's book gives many applications and possible uses for hydrosols.

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