This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
No essential oil possesses a greater degree of interest for the practical bottler of carbonated beverages than oil of lemon. Unfortunately it is but too true that very few are prone to more rapid deterioration than this interesting flavoring material. The essential oil of lemon is secreted by nature in little vesicles in the peel of the ordinary lemon, the citrus limonum of botanists. This beautiful tree, which is frequently cultivated in hot-houses, belongs to the natural order of the Aurantiacem, being closely related to the orange, the lime, the bergamot and others. The candied peel of a very near relative furnishes us with citron, which is largely used by bakers.
At the present time lemons are cultivated for the production of the oil on a very large scale in Sicily and Reggio in Calabria, and to a small extent also at Mentone and Nice in France. In Sicily and Calabria the production of the oil takes place chiefly in November and December. The finest varieties are obtained by the old-fashioned process of hand pressure. This is performed by removing the peel in longitudinal slices, leaving them until the next day, when a small sponge is applied to the external surface and the peel is at the same time pressed into a direction opposite to that in which it grew, namely, making the surface strongly concave instead of convex. By this mode of procedure the vesicles are ruptured, and the oil which spurts out from them is absorbed by the sponge lying in contact with the peel. The workman gives four or five squeezes to the slice of peel and then throws it aside. When the sponge has become saturated in this manner, it is forcibly wrung out into an earthen bowl. The oil soon separates from the watery liquid, on the top of which it floats, so that it can be readily removed. By this method three and a half ounces, on an average, are procured from about one hundred lemons. Although this so-called sponge process appears to be crude and wasteful, it nevertheless yields an excellent product. An inferior quality is obtained by subjecting the expressed pieces of peel to subsequent distillation.
In France the oil is separated from the peel by a funnel furnished with a number of stout, sharp brass pins, which liberate the oil from the cells when the lemon is rubbed on them. A colorless oil of very inferior fragrance is also obtained by distillation.
Lemon-oil loses part of its fragrance by heating; the finest qualities are therefore not obtained by distillation, but by mechanical means, pressing, etc.
The oil should be of the most recent crop. That which is first made in November from unripe fruits is generally regarded as the finest of all. The expressed oil of lemon has more pure aroma than the distilled oil, but does not keep so well.
Distilled oil of lemon is colorless, while the expressed article has a bright golden yellow color. When the distilled is mixed with the expressed, the color is rendered somewhat paler. A pale or dull-colored oil should therefore be avoided.
Expressed oil of lemon always contains a white albuminous substance which makes it appear turbid. As soon as the cans are opened, the oil should be filtered, to free it from the albuminous material. The odor and taste of the oil should be carefully examined, and only that which is almost identical with the fresh lemon peel should be employed.