Absolute (substance)
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Similar to essential oils, absolutes are concentrated, highly-aromatic, oily mixtures extracted from plants. Whereas essential oils can typically be produced through steam distillation, absolutes require the use of solvent extraction techniques. First, an organic solvent, such as hexane, is added to the plant material to help extract the hydrophobic compounds. This solution is filtered and concentrated by distillation to produce a waxy mass called concrete. The lower molecular weight, fragrant compounds are extracted from the concrete into ethanol. When the ethanol evaporates, an oil (the absolute) is left behind.
Though absolutes are usually more concentrated than essential oils -- the efficiency and low temperature of the extraction process helps prevent damage to the fragrant compounds -- solvent extraction can be considered an inferior method since it can leave behind traces of the solvent. In aromatherapy, these traces are considered undesirable since they could cause allergies and effect the immune system. In perfumery, these traces may produce off notes in the final product.
Absolutes are used extensively in perfumery applications. With a good knowledge of the solvent they are using, extractors can produce absolutes having an aroma closer to the original plant than is possible with essential oils produced through distillation. Examples of this are rose otto (steam distilled rose oil) compared to rose absolute or neroli (steam distilled oil from the blossom of the bitter orange tree) compared to orange blossom absolute. Furthermore, some botanicals are too delicate to be steam distilled and can yield their aroma only through solvent extraction. Examples of this are jasmine, tuberose, and mimosa.
