Expression (Preparation of Volatile Oils) Expression A number of volatile oils mostly undergo decomposition on being subjected to distillation. Likewise, volatile oils found in the rind of the fruit, such as: orange, lemon and bergamot peel, are best obtained by extrusion i.e., by the application of pressure. Even on a commercial scale these oils are produced by extrusion so as to preserve the natural fragrance that otherwise get deteriorated by distillation process.
In actual practice, however, the expression may be accomplished by any one of the four following processes, namely:
(a) Sponge Method: The citrous fruit (e.g., orange, lemon, grape fruit, bergamot) is first washed to remove the dirt, and then cut into halves to remove the juice completely. The rind is turned inside out by hand and squeezed when the secretary glands rupture. The oozed volatile oil is collected by means of the sponge and subsequently squeezed in a vessel. The oil floating on the surface is separated.
(b) Scarification Process (Ecuelle a Piquer): Ecuelle a piquer is a specially designed apparatus
(Fig. 5.2) first introduced on the Revieras in France, which is nothing but a large bowl meant for pricking the outer surface of citrous fruits. It is more or less a large funnel made of copper having its inner layer tinned properly. The inner layer has numerous pointed metal needles just long enough to penetrate the epidermis. The lower stem of the apparatus serve two purposes; first, as a receiver for the oil; and secondly, as a handle. Now, the freshly washed lemons are placed in the bowl and rotated repeatedly when the oil glands are punctured (scarified) thereby discharging the oil right into the handle. The liquid, thus collected, is transferred to another vessel, where on keeping the clear oil may be decanted and filtered.

 Ecuelle a Piquer
Fig. 5.2 Ecuelle a Piquer
(c) Raspings Process: In this process the outer surface of the peel of citrous fruits containing the oil gland is skillfully removed by a grater. The ‘raspings’ are now placed in horsehair bags and pressed strongly so as to ooze out the oil stored in the oil glands. Initially, the liquid has a turbid appearance but on allowing it to stand the oil separates out which may be decanted and filtered subsequently.
(d) Mechanical Process: A substantial quantum of volatile oil across the globe is now prepared by various mechanical means solely based on the above principles. However, the use of heavy duty centrifugal devices may also be incorporated so as to ease the separation of oil water emulsions invariably formed. It is pertinent to mention here that with the advent of modern mechanical devices the oil out put has increased appreciably and the older methods have only remained for the sake of history.

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