This method is practical for citrus because of the unique oil bearing structure of citrus fruit rind. Most oils are extracted using steam distillation, during which the plant material is permeated with steam. As the plant tissues break down, the essential oils and water vapor are released, then collected and cooled. The volatile essential oil condenses, separates and is easily isolated. Solvent extraction is used when the odorous properties of delicate flower and plant material would be altered or destroyed by steam or water distillation or when a plant, for instance rose absolute and jasmine contains very little oil, making steam or water distillation impractical.
Solvent extraction produces a concrete which in turn is refined into an absolute.
To produce a concrete, the plant material is gradually saturated with a hydrocarbon solvent. The solvent dissolves the plants constituents including essential oils, fatty acids and waxes. After the solvent is distilled off the remaining constituents make up the concrete. The essential oil is extracted from the other constituents with alcohol. The fatty acids and waxes are not alcohol soluble so they're left behind.