The primary method for extracting essential oils is through steam distillation. In this process, steam is generated in a separate boiler and then passed through botanical material in a still. This action softens the cells, enabling the essential oil to be released in vaporized form.
In the distillation of two dissimilar liquids, such as water and essential oil, each exerts its own vapor pressure as if the other were absent. When the combined vapor pressures equal the surrounding pressure, the mixture reaches a boiling point. Essential oil components, typically with boiling points up to 300°C, subsequently undergo evaporation.
After evaporation, the steam and essential oil undergo condensation and separation. Biomass steam distillation usually yields two products: a relatively pure essential oil and an aqueous condensate called a hydrosol. The essential oil consists of hydrophobic, often aromatic compounds produced in minimal concentrations as secondary metabolites in plants. Conversely, the hydrosol contains secondary metabolites that are more hydrophilic.
Essential Oil Extraction Basics
