Essential oils are fragrant oils that exist in the flowers, leaves, stems, bark, peel and other parts of plants. Essential oils are also called volatile oils because they evaporate when exposed to air. Many different types of plants have an essential oil. Examples of these are flowers like rose, gardenia, carnation, and jasmine. Citrus fruits, like orange, lemon and lime, also have essential oils. Other plants that have an essential oil are nutmeg, cinnamon, cloves, and black pepper. Whenever you peel an orange, some of the essential oil in the peel squirts out, and this is what you smell as you are peeling the orange.
Essential oils are removed from flowers and plants by three basic methods: steam distillation, expression, and extraction.
Using this method, the fragrant parts of the plant are put in a device called a "still." Steam is allowed to permeate the plant material. As the steam rises it loosens the essential oils in the plant parts and carries it to a separate container. The steam is condensed into water in this separate container and the essential oils are removed from it there.
This method is used for removing essential oils from the peels of citrus fruits like orange, lemon, and lime. In expression, the peels are squeezed, or punctured, to remove the essential oils.
This method is used for removing the oils from delicate flowers such as jasmine, carnation and gardenia. It is also used for removing the oils from resins such as frankincense and myrrh. In this method the essential oils are removed from the plant or resin by soaking it in fat, oil, or a chemical solvent. When the solvent has been removed, the fragrant oil that remains is called an “absolute.” When the solvent has been removed from a resin, what remains is called a resinoid.