Essential oils are biologically important substances produced by aromatic plants that are stored in specialized glands, roots and leaf hairs. Among their many functions they can act as insect repellants and pollinator attractants or serve as antimicrobial agents when under attack – but to most humans, they simply smell good. Essential oils may be released from the plant and collected (concentrated) under the conditions of high-pressure steam distillation and sometimes hydro- or water/steam distillation, or a combination thereof.
Distillation is a method of separating components based on differences in evaporation rate of volatile constituents through temperature, pressure and subsequent condensation taking place within the still. The essential oils contained in plants are insoluble in – and have a higher boiling point – than water, allowing the essential oil to vaporize at a lower temperature than it normally would on its own.
Water/Steam Distillation is a high-yield process and is used for most aromatic plants yet, due to low pressure, requires a longer distillation time to extract all the volatiles. Direct steam distillation involves bubbling steam through the plant material and is suitable for aromatic plants with lower temperature needs. Hydrodistillation involves covering the plant material in water prior to longer distillation times and is useful for some resins, spice powders and chopped roots or bark.
Cohobation describes a process of re-distillation, or an extra evaporation/condensation of previously distilled, aromatic distillate water, and is exclusively used to maximize the yield of rose ottos and to fortify their hydrosols. In addition to enriching the yield of essential oil, the dissolved, more hydrophilic volatiles are also concentrated in the hydrosol as a result of cohobation, making it more stable, extra fragrant and maximally therapeutic.
Molecular Distillation is a process using only extremely low vacuum pressure, and for this reason it is also called ‘vacuum distillation’. Molecular distillation lowers the boiling point of liquids in a molecular still and is used to separate and remove undesirable molecules such as colorants, or to concentrate heat-sensitive molecules such as fatty acids. Molecular distillation also eliminates the low-boiling, ‘dirty’ top notes, resulting in a refined, super suave aroma.