Essential oils are the volatile, powerfully concentrated odorous principles of plants.
Different processing methods are required to extract essential oils from different plants. Citrus oils including sweet orange, bergamot and grapefruit are expressed oils. The expression method uses pressure to physically squeeze the oil from the plant tissue. This method is practical for citrus because of the unique oil bearing structure of citrus fruit rind. Most oils are extracted using steam distillation, during which the plant material is permeated with steam.