The term “essential oil” originated when the earliest practitioners of medicine spoke of the Quinta essentia (quintessence) of a drug that was, to them, the most sublime extractive. It represented the efficient part of the drug. In time, the term “essential oil” was used to represent that part of the plant or fruit necessary for the characteristic flavor or other useful property of the natural product. A citrus essential oil is the part of the fruit (located in the peel) necessary for the characteristic flavor of that particular fruit. In recent years other flavor fractions such as distilled oils or distilled aqueous aroma solutions (essences) have been developed for use in flavoring citrus products. But the essential oil from the peel still remains a basic flavor ingredient in most citrus products.
The major cold-pressed citrus peel oils recovered commercially and listed in order of their increasing commercial value are orange, grapefruit, mandarin, lemon, and lime; cold-pressed lime oil is only slightly more valuable than lemon oil. In commercial methods of peel oil recovery, the oil sacs are mechanically ruptured and the oil is washed away from the peel with water; some pressing action usually is involved. The resulting oil-water emulsion is separated by centrifugation. Sometimes enzymes, emulsion-breaking agents (e.g. Dupanol), and heat are used for maximum yield of the valuable oils of lemon and lime.