The second acceptable extraction method for the production of essential oils is the cold squeezing of citrus peels (Lemon, Orange, Grapefruit, Mandarin, Bergamot, and so on). In general, the method consists in the compression or pricking of the pockets full of essence on the surface of the citrus peel, and then in the collection of the essence thus liberated. The method is very different from steam distillation and therefore the product obtained will be different from the distilled essential oils (so much so that some authors prefer to call these “essences” instead of essential oils. I prefer to stick with essential oil because essence is an ambiguous term). The product will have characteristics that are closer to those of the essence present in the plant matrix, because in the extraction there is no distillation filter and the temperatures are much lower.
Generally speaking, the essential oil from cold pressing is richer and more complex than that of distillation because in addition to all volatile molecules it also contains non-volatile ones that are too heavy to be distilled but are still fragrant. Among these non-volatile compounds there are also non-perfumed and unattractive ones, such as waxes and paraffins, and fragrant compounds which present risks such as furocumarines, molecules that cause phototoxicity problems. Finally, pressing can allow the passage of non-volatile pesticide residues.
For this reason on the market there are citrus essences called FCF, or FuroCumarin Free, e.g. free of furocumarine. To eliminate these toxic molecules, essential oils are subjected to fractional distillation or to chemical processes that allow to isolate and eliminate most of the furocumarines and make the substances more usable in cosmetics and perfumery. Of course if instead of pressing the skins we distilled them, we would have essential oils already without furocumarine. The reason why this is not normally done is that distillation oil is, as I said, less attractive from the perfumery point of view.
Whereas in the past the method of obtaining citrus essences was extremely slow and expensive because it meant processing the “skins” of the Citrus fruits by hand, nowadays the process is highly mechanized and almost always secondary to the fruit juice industry.
The main modern methods are that of the Pelatrice, where the fruits are crushed and punctured to release the essence, which is then washed away and harvested by means of a spray of water; that of the Brown Extractor, where rotating rollers with tips puncture the cells; that of the Sfumatrice, where the peels already emptied of the pulp and macerated for a day are passed through a compressor roller that bursts the cells; that of the Brown Peel Shaver, where the skins that have already been emptied are cut into four and passed into a system of compression rolls and blades that remove the white part (albedo) from that rich in essences (flavedo) and squeeze the essences from the latter; and that of the FMC Extractor, consisting of a pressure mechanism that simultaneously squeezes and wringes the peels, aspires pulp and juice and separates them. As with the other apparatus, a water spraying washes out the essence which is then harvested, filtered and separated by centrifugation.
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