This set of “high pressure, low temperature” extraction methods began in the 1980s. The instruments and equipment are very complicated and expensive. The essential oil is labeled “CO2 Extraction”. This extraction is carried out in a closed reaction tank, and the time required is very short, in just a few minutes (distillation takes at least 1 hour).
The principle is to first extract the aromatic molecules of the plant by using the liquid state of carbon dioxide under high pressure; and then use the change of pressure to easily vaporize the carbon dioxide to obtain the essential oil.
Compared with the orthodox distillation method, the essential oil obtained by the carbon dioxide extraction method is perfect because of the low temperature and the aroma. It contains less ene, more esters, and is closer to the state of the natural plant. This extraction method does not apply to all essential oils and sometimes produces some emulsions.
Although the plant essential oil extracted in this way will be very close to the original aromatic composition in the plant, it is a perfect extraction method. However, the equipment used in this extraction method is not only large but also very expensive. Taking it to extract essential oils often takes several years to balance costs. Until today, the price of essential oils extracted with supercritical carbon dioxide is still very expensive.
This extraction method is far more complicated than what is described in the book. Simply put, the carbon dioxide gas is pressurized to a very high degree (such as 3 inches below sea level, 200 times atmospheric pressure), so high. Pneumatic gases dissolve the aromatic essential oils in plants. When the pressure is reduced (down to 100 times the atmospheric pressure), then the carbon dioxide will change from a liquid to a gaseous state, so that the plant essential oil still in a liquid mist state can be separated and collected. Compared to solvent extraction, this extraction method does not leave any solvent residue. Of course, some people also question that carbon dioxide is an acid gas, so this type of extraction will more or less destroy the chemical structure in the essential oil.
Generally speaking, the essential oil extracted by the supercritical carbon dioxide method has a small proportion of terpenes, and the esters are high, and there are some macromolecular substances which cannot be extracted by distillation. Since the terpene in many essential oils is a product of the change through the distillation process, the supercritical carbon dioxide extraction essential oil with less terpene (the composition ratio of other chemicals is also relatively different) will be closer to the original essence in natural plants. structure. Surprisingly, it is not necessarily close to nature. Taking ginger as an example, the essence of ginger oil extracted with supercritical carbon dioxide is naturally better than distilled ginger oil, but it is also easy to stimulate sensitive skin. In addition to being expensive, there is a shortcoming in the essential oils extracted from supercritical carbon dioxide, which is that few manufacturers are willing to provide and are not easy to buy.