Part 3: Distillation Methods—Expression (Cold Pressing)
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Expression is most commonly used to obtain essential oils from citrus fruits such as oranges, bergamot, grapefruits, lemons, and limes. This method involves the rind portion of the fruit, or the outermost waxy layer of the fruit’s peel. Unlike steam distillation, this method does not require a heat source, so it is often referred to as “cold pressing.” To begin, the fruit is placed in the expression machinery where it is passed across rasping cylinders that cut up the surface of the peel. As this process occurs, small sacs containing essential oil break open and release their contents. Water is sprayed over the fruit to collect the essential oil. At this point the essential oil is still mixed with some watery materials from the fruit’s flesh and some solid particles from the rind. To isolate the essential oil, this mixture is filtered and centrifuged, allowing separation of the pure essential oil product from any water or solid particles. Expression provides high quality products with characteristic fragrances nearly identical to the starting fruit. This method is most useful with plant materials that lose their fragrance and beneficial properties when exposed to the temperatures required for steam distillation.