Olfactory Chemistry: The Physics of Supercritical Fluid Extraction- It’s a Gas, Gas, Gas

For years the extraction of the essential oils from natural sources was done via extraction in hot ethanol and distillation of the resulting solution to collect the essential oil. This process due to the heat used for the extraction and the distillation causes loss of some of the ingredients which are heat sensitive or reactive with alcohol when it is heated to boiling this is called denaturing. What this means is the process does not get the whole spectrum of ingredients that come from the natural source. The only alternative to this steam extraction and distillation process was the very labor intensive enfleurage which would capture a fuller amount of the natural products but still not everything.

Then along came supercritical fluid extraction. This is a process where a solvent which exists at a gas at normal pressure and ambient temperature when placed under pressure and cooled, liquefies. If there is a source of essential oils covered by the cold liquid it extracts everything out of it. After the extraction is done the liquid is transferred into a vial where it is allowed to return to room temperature and pressure. This turns it back into a gas leaving behind the essential oil. Are your eyes glazing over yet? This is always where I see the light going out of the eyes anyone I have ever tried to explain this to. You know the whole adage about a picture being worth a thousand words? Well the video below which comes from Mane describing their Jungle Essence procedure is worth a million words as it is a beautiful way of showing how this is done.

The solvent used in the video is probably primarily butane, the gas used in cigarette lighters. When used as the solvent in supercritical fluid extraction it performs well. The first solvent used was carbon dioxide and those early essential oils were labeled CO2 to indicate that they were extracted with that. Now all of the aromachemical houses have worked to perfect different blends using other blends mostly using a high percentage of butane.

When I was at the Mane presentation at Pitti they showed the video above and they passed around examples of raw materials which were extracted the traditional steam distillation way, using carbon dioxide as a supercritical fluid, and using their Jungle Essence blend. It was striking to see how much more there was in the supercritical fluid extractions. The most striking was an extract of hot Szechuan pepper. A glass of the ground pepper pods was passed around followed by a mouillette of the Szechuan pepper Jungle Essence. If I was blindfolded I wouldn’t have been able to tell the difference. Petitgrain was also an interesting example because in that case the essential oil realized by steam distillation was only very slightly different than the Jungle Essence version. That showed me that supercritical fluid extraction is not always the best choice.

I hope that the video above especially helps you to understand the technique much better than my overly technical second paragraph and the next time you see a note which says something like sandalwood EO CO2 you’ll understand why it might smell a little different.

My thanks to Mane for the video I really do think it is very well done.

Mark Behnke

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