Used in perfumery and aromatherapy, absolutes are similar to essential oils. They 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 or more traditionally, through enfleurage.
First, an organic solvent, such as hexane, is added to the plant material to help extract the non-polar compounds. This solution is filtered and concentrated by distillation to produce a waxy mass called concrete. The more polar, fragrant compounds are extracted from the concrete into ethanol. When the ethanol evaporates, an oil—the absolute—is left behind.
Character and use
Absolutes are usually more concentrated than essential oils. Also, the efficiency and low temperature of the extraction process helps prevent damage to the fragrant compounds. With a good understanding of the solvent they are using, extractors can produce absolutes with aromas closer to the original plant product than is possible with essential oils produced through distillation. Examples of this are rose otto (steam distilled rose oil), as opposed to rose absolute, and neroli (steam distilled oil from the blossom of the bitter orange tree), as opposed to orange blossom absolute. Also, some raw materials are either too delicate or too inert to be steam-distilled and can only yield their aroma through other methods, such as solvent extraction or lipid absorption. Examples of these are jasmine, tuberose, mimosa, and beeswax.
This production method may leave trace amounts of solvents in the absolutes. Therefore, some absolutes are considered undesirable for aromatherapy. However, absolutes are used extensively in perfumery because the aromatic compounds in absolutes have not undergone processes involving high temperatures. This makes them often smell fresher. Although the solvent traces could produce off-notes in the final product, this is usually not a problem if the absolute is of a decent quality.
- Karl-Georg Fahlbusch et al. (2007), "Flavors and Fragrances", Ullmann's Encyclopedia of Industrial Chemistry (7th ed.), Wiley, p. 83