Part 3: Distillation Methods—Solvent Extraction


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Solvent extraction can be used on every type of plant material, but is most commonly used on flowers that are extremely fragile or cannot otherwise endure the conditions required for steam distillation. Solvent extraction methods produce absolutes, which are different from essential oils because they can contain both aromatic and non-aromatic chemical constituents. Choosing a good solvent is an important first step. Typically, less polar compounds (such as pentane or hexane) or alcohols (such as methanol or ethanol) are used as solvents. The type of solvent used can alter the absolute, so it is important to choose a solvent that will make minimal alterations to the unique fragrance and beneficial properties of the absolute.

The plant material is placed in a shallow tray and washed with a layer of the selected solvent to dissolve out the fragrant compounds. In order to allow the solvent to thoroughly penetrate the plant material, this process may involve physically breaking up the plant material or spinning it in a rotating drum. The resulting mixture is then filtered to remove the plant material and vacuum distilled to remove excess solvent. The yield of this process is a thick, waxy material called a “concrete.” Concretes contain all of the potent fragrant compounds of the plant as well as a variety of other lipid soluble compounds. The concrete is further processed with a second solvent (usually an alcohol like ethanol). The absolute is soluble in this solvent but the other lipid components are not. After another round of vacuum distillation to remove the solvent, a pure mixture of only absolute remains. Only 1–5 percent of the solvent will remain in the final product. Common absolutes extracted by this method are jasmine and vanilla. Solvent processing is known for producing absolutes with rich, authentic fragrances.

 

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