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Essential oils are derived from plants by distillation using water or steam. After condensation of the vapor phase, the oil is separated from the aqueous phase to be subsequently removed.

The performance in obtaining essential oils based on the concentration of oil in the plant is about 1%.

Essential oils consist of volatile lipophilic substances, mainly hydrocarbons or monofunctional compounds derived from the metabolism of mono-and sesqui-terpenes, phenylpropanoids, amino acids and fatty acids. We must distinguish between essential oils called "spirits" which are products containing ethanol, these plants are also obtained by distillation with ethanol or ethanol-water mixtures.

The oils obtained from processing citrus fruit peels are a special type of essential oil. These are isolated by pressing the skin to separate the volatile substances in the pericarp stored in small oil glands. The resulting products are called essential oils because they consist largely of highly volatile terpene hydrocarbons. However, they also contain small amounts of permanent compounds, such as dyes, waxes, and furocoumarins.

Most essential oils are used directly as raw materials in the production of flavor compounds and fragrance. However, some essential oils are fractionated or concentrated by distillation, division, or adsorption. Substances that are removed are important for the desired characteristic odor and taste, and separated from other components, which have an unpleasant odor or very weak or are unsuitable for use in question.

The individual compounds can be isolated from essential oils that contain one or only some important components using distillation or crystallization.

Examples are: eugenol from clove oil, menthol, peppermint oil, eucalyptus oil citronellal, etc. These compounds are used as such or serve as raw materials for the synthesis of derivatives, which are also used as substances for flavors and fragrances.

However, the importance of some of these oils has decreased substantially due to the development of selective synthetic processes to obtain these components.

While essential oils and their fractions are mixtures of many substances, these oils are converted from time to time together in derivatives.