Essential Oils

Essential oils are concentrated, hydrophobic liquids that contain volatile aroma compounds extracted from plants. Also known as volatile oils, ethereal oils, or aetherolea, these oils are named for the plant from which they are derived, such as oil of clove. The term "essential" refers to the distinctive scent, or essence, that the oil imparts from the plant. While essential oils do not need to share specific chemical properties beyond their characteristic fragrances, they are known for their potent aromas.

Typically, essential oils are extracted through distillation, although other methods include expression and solvent extraction. They are commonly used in perfumes, cosmetics, soaps, and other products, as well as for flavoring food and beverages and for scenting incense and household cleaning items.

Historically, various essential oils have been employed for medicinal purposes. Claims made by sellers of medicinal oils range from skin treatments to cancer remedies, often based on traditional uses. These claims are regulated in many countries, leading to increasingly vague statements to comply with legal standards.

In recent decades, essential oils have gained renewed interest due to the rise of aromatherapy, an alternative medicine practice suggesting that specific aromas from essential oils can have therapeutic effects. Essential oils are used in aromatherapy through methods such as massage with diluted oils, air diffusion via nebulizers or candles, or burning as incense.

The extraction techniques for essential oils have evolved significantly over time. Ibn al-Baitar (1188-1248), an Andalusian physician and chemist, was among the first to document these methods.

Many flowers contain insufficient volatile oil to be extracted through expression, and their delicate chemical components may be damaged by the high heat of steam distillation. Instead, solvents like hexane or supercritical carbon dioxide are used. Hexane extraction yields concretes, which are mixtures of essential oil, waxes, resins, and other plant materials. Because concretes contain significant amounts of non-fragrant waxes and resins, further processing is required. Ethyl alcohol, which dissolves only the fragrant compounds, is used to extract the essential oil from the concrete. The alcohol is then removed by distillation, leaving behind a more refined product known as an absolute.

Supercritical fluid extraction using carbon dioxide is another advanced method. This technique avoids petrochemical residues and prevents the loss of some volatile compounds that occur with steam distillation. Supercritical carbon dioxide extracts both the waxes and essential oils, which are then separated by lowering the extraction temperature. This process preserves the integrity of the compounds. The carbon dioxide reverts to a gas when pressure is reduced, leaving no residue behind.

Supercritical carbon dioxide is also employed in decaffeinating coffee, though the process differs in scale and application from essential oil extraction.