Humans have stopped to smell the roses for eons!
The enormous variety of aromatic plants and their scents have enchanted us for millennia. It's no surprise that we would figure out how to extract the oil and take it with us, wherever we may roam!
You can imagine that depending on the plant and the plant part we extract from, we would need to use more than one extraction method. Below are descriptions of the most common methods of essential oil extraction: steam distillation, cold pressing, and solvent extraction.
Steam distillation is the most common method of extracting essential oils from the plant.
Fresh or dried plant material is put into a still, and pressurized steam is generated and circulated through the plant material. The heat of the steam opens the specialized cells or glands to release the essential oils. As the essential oil is released, it travels with the steam molecules through a tube into the still’s condensation chamber. As this mixture cools, it condenses into oil and water. The essential oil then naturally separates from the water.
Steam distillation yields a very “pure” form of essential oil, in that only water and heat are used in the extraction process. Steam distillation is used for many flowers and leaves, such as lavender, ylang ylang and peppermint. It is also used for woody plants and the tree oils like cedarwood. This type of distillation can also be used for some delicate flowers, such as rose.
In this method the peel of the fruit is grated while rolling over a trough. The tiny specialized cells which contain the essential oil are punctured. Then the fruit is pressed to squeeze the juice and the essential oil from the pulp. The essential oil rises to the surface of the juice and is then separated by a centrifuge. We saw this process in Italy with bergamot, and it was amazing to watch (and smell). Here are a few pictures.
-The cold pressing machine that produces the lovely Bergamot oil.
-The distiller puts the bergamot fruit into the conveyer belt to be rinsed and grated.
-The fruits are being washed and sent up to the grater.
-The fruit rinds are being grated, as the essential oil is concentrated in the rind.
-The essential oil from the pressed fruit rinds!
This method is most often used for delicate flowers (like Jasmine, pictured to the right) that would simply dissolve in the heat of distillation. A solvent compound is poured over petals and buds and the essential oil dissolves itself into the solvent. Solvents vary from the newer method of using carbon dioxide or the environmentally hazardous liquid butane, to crude alcohol, or even more toxic chemicals such as ether, hexane, benzene, or other petroleum-based compounds.
The result is a semi-solid material referred to as a concrete. Often times a concrete is used in perfumery. It will contain waxes and residues, which must be filtered away and purified using alcohol washing, freezing and a low, gentle vacuuming. This process produces what is called an absolute.
The advantage of this method is that it uses a low temperature range and low pressure, allowing the flower’s pure fragrance to be captured (this is very appealing to perfumers). The disadvantage of an absolute is that when the process is not done with expertise, the chemicals used in the extraction process may remain present in the oil. This presents the possibility of skin sensitization or irritation.
There are several other extraction methods. However, steam distillation, cold pressing, and solvent extraction are currently the most common. The CO2 method of extraction, although new in its beginnings, is starting to become more widely used with select distillers.