Essential Oils are produced from plant materials through steam- or hydro-distillation, or through cold-expression of citrus oils.
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Essential Oils are produced from plant materials through steam- or hydro-distillation, or through cold-expression of citrus oils.Water or Steam Distillation
This is the most widely used and most economical method of extracting essential oils. The process requires a great deal of skill and knowledge as there are many variables involving time, temperature and type of plant being distilled. Also, some plants are distilled immediately upon harvest, some are partially dried and some may require to be completely dry before distillation. Basically, the plant material is placed above boiling water (water distillation) or in a separate chamber where steam passes through (steam distillation). The latter is sometimes called dry distillation if done under pressure. The advantage of steam distillation over water distillation is that raw material does not come in contact with boiling water. The heat and steam cause the structure of the plant cells to break down, releasing the essential oil. The steam and essential oil are then channeled through a cooling coil, where they condense and return to a liquid state, comprised of both water and essential oil. Most essential oils will float to the top; heavier oils such as clove will sink to the bottom. The two are then separated, using a separatory funnel or by siphoning. The water remaining after this process is called a hydrosol and contains minute amounts of the essential oil and other water-soluble plant constituents.
In this method, plant material is charged in the still, water is added to immerse the charge, leaving sufficient vapor space. The quantity of water should be adequate for the plant material to move freely in boiling water and avoiding localized overheating. The water is heated under direct fire or steam jacket, or in some cases a closed steam coil. It may be necessary to add water during the distillation process to prevent dry material from being exposed to direct heating. The steam vapor produced is condensed and oil is separated from the water as in steam distillation. Water distillation is used when the plant material may form large compact lumps through which steam cannot penetrate. Water distillation is a slower process than steam, requiring more stills, more space, more fuel and is the least economical of the methods using water. Certain components (esters and aldehydes) can deteriorate under prolonged contact with boiling water, and some water-soluble components cannot be completely recovered.
Another way to obtain essential oils uses no water or solvents, and is reserved exclusively for the peels from members of the Citrus family such as Bergamot, Orange, Mandarin and Lemon.
Expression or Cold Pressing
Citrus contains small essential oil sacs, located just beneath the surface of the peel. Originally, pressing by hand was required, obviously a labor-intensive process. Now, the majority of Citrus peel oil is expeller pressed using efficient mechanical presses.