Supercritical CO2 Extracts - Are They Merely Essential Oils?

Posted by Lauren Bridges on

Ken Miller, Functional Aromatic/ Herbal Practitioner of WholeAroma, LLC wrote a brilliant post discussing recent debate in the aromatherapy community on whether or not supercritical CO2 extracts can rightly be referred to as essential oils. The subject sparked much debate, and he was able to write a piece clarifying the issues at hand and why supercritical CO2 extracts must be acknowledged as such without painting them as something else. A massive thank you to Ken for allowing me to host his piece on this site. Quick note: I want it to be clear that Ken Miller wrote this piece. My site blog will not allow me to change the noted author, which is the only reason my name is noted instead of Ken's. That all being said, please enjoy this wonderful and educational piece!


If you have been following the aromatherapy community in the last few weeks, you have probably seen the debate over the subject of supercritical extracts. A book by author Scott Johnson entitled “Supercritical Essential Oils” fostered the debate. The contents of the book itself were not included in the debate, but rather the debate circled around whether or not supercritical CO2 extracts could (or should) be termed “essential oils” — specifically “select” supercritical CO2 extracts.

The book author asserted the following:
  1. That because of the similarities in the major components of select supercritical CO2 extracts with the steam-distilled product, select supercritical CO2 extracts could (and should) be defined as “essential oils.”

  2. Many research papers refer to select supercritical CO2 extracts as “essential oils” in their titles and/or in the content of their published works, and therefore aromatherapy should be following the lead of the research scientists whom the author claims are the authority on these matters.
Are these assertions correct? Are select supercritical CO2 extracts so close to the steam to hydro distilled product that the aromatherapy community should, in fact, be generalizing them as “essential oils?”

What Is An Essential Oil?

To begin our discussion, we must first define “essential oil.” According to the International Organization for Standardization (referred to as ISO hereafter), an essential oil is defined thusly:

"An essential oil is a product made by distillation with either water or steam or by mechanical processing of citrus rinds or by dry distillation of natural materials. Following the distillation, the essential oil is physically separated from the water phase.”

This is the definition upon which the entire aromatherapy community has based its teachings and literature for decades. An essential oil is a steam-distilled product or hydro-distilled product; furthermore, included in this definition is the oil obtained from the mechanical processing of citrus rinds, etc.

The argument by the book author is that this definition is 20 plus years old and was created at a time that supercritical CO2 products in general did not exist. Therefore, he argues, the definition should be revised to include select supercritical CO2 products.

But would it be profitable to include select supercritical CO2 products in that ISO definition? What would be the consequences of altering that definition?

Are Select Supercritical CO2 Products Different Than Essential Oils?

The claim by the author of this book is that select supercritical CO2 products are similar enough in nature such that they should be considered “essential oils” He asserts that the major components are essentially the same, so the end justifies the means. In other words, because the properties of select supercritical CO2 products are so similar to major components to the steam or hydro distilled product, grouping them into the definition of “essential oil” is justified.

The problem with this assertion is two-fold:
  1. The minor components will vary, and those minor components do matter. We often think of Rose essential oil, for example, where some of the minor components have been identified as the most medicinal.

  2. Furthermore, there are often components in the select supercritical CO2 extract that are not at all present in the essential oil.
Yes, there are some select supercritical CO2 extracts that are so close to the essential oil in even minor components that one might justify the assertion that it is basically an essential oil, but there are a myriad of cases in which this justification is unwarranted. There are many examples of this, and here a couple.
German Chamomile select supercritical CO2 is quite different from the steam or hydro distilled product (essential oil). One of the most marked differences is its lack of the compound chamazulene. Chamazulene is an artifact of the steam distilled or hydro distilled product, created (and almost completely consumed) by the conversion of matricin via the application of heat. In the select supercritical CO2 product (and the Total product as well), the matricin fully remains. While chamazulene in the steam distilled product is itself considered a powerful anti-inflammatory, matricin has been estimated to be ten times more powerful in anti-inflammatory property. In addition, the component α-bisabolol in the steam or hydro distilled product is often less than one percent, while in the select supercritical CO2 extract it is around 43%. On these two factors alone, it is quite a reach to attempt to classify this product as an essential oil.

Frankincense (carterii) select supercritical CO2 is also quite different from the steam or hydro distilled product. Although it shares many of the major components of its steam or hydro distilled counterpart, the select supercritical CO2 contains diterpenes that are not found in the steam or hydro distilled product — namely incensol, isosembrene, cembrene A, and incense acetate. These compounds alone differentiate, and they also change the therapeutics of the product, most especially from a mental and emotional treatment standpoint.
Beyond the examples above, it is also worth note that almost all supercritical CO2 extracts (select and total) will contain some non-volatiles. In select supercritical CO2 extracts, the non-volatiles will be minute, but they will be there; in the total supercritical CO2 extracts they will be quite prominent. Whether the major components of the volatiles from both the supercritical extracts and steam or hydro distilled extracts are similar, there are no non-volatiles in steam or hydro distilled products. Furthermore, GCMS testing will only reveal the volatiles, and that is all the testing that is really needed to determine composition for steam or hydro distilled products, while all supercritical CO2 products will need HPLC testing.

Should Aromatherapy and ISO Follow the Research Scientist?

The second argument presented by the author of the book (or rather book title) in question, is that because many research scientists will used the term “essential oil” in their published works when the extraction is later revealed as a select supercritical CO2 extract, the research scientist has thus equated a steam or hydro distilled product (essential oil) to the select supercritical CO2 extract, and therefore ISO and aromatherapy at large is not “keeping up with the times” nor is it “keeping up with science.”

The problem with this argument is that researchers are not the authorities on the definition of the two products. And the further problem with this is that more often than not, researchers fail to make distinctions because of, well, either pure laziness or because they really don’t understand or care to understand the distinction. How many of us practitioners, vendors, and students have read the title of an article in our research, observed that “essential oil” is mentioned, and then began to read the article only to find that the extraction method is not steam or hydro distilled, but rather supercritical, or even an alcoholic extraction (methanol or ethanol in particular)? I know that I have seen this more times than I can count. So, do we now say that an alcoholic extraction should now be considered an essential oil because the authors of the research paper (scientists) have decided to make that claim in their title? Should we now also include absolutes in the definition of essential oils because a research scientist says so in a publication?

The fact remains that ISO and the aromatherapy community are in a much better position to make the delineations because those bodies are most knowledgable about the subject matter, here’s why.


It’s All About the Therapeutics…and the Client Notes

One of the most important reasons why absolutes, supercritical extracts, and even florasols are not included in the definition of “essential oils” is because of the therapeutics. As mentioned above, the select (and total) supercritical CO2 extracts may differ greatly in properties, and most importantly in dose compared to the steam or hydro distilled product.

A good example of this among the select extracts is surprisingly Peppermint. The menthol content of the select supercritical CO2 is about 24%, while the steam distilled product is about 50%. According to aromatherapy practitioner Madeliene Kerkhof who specializes in end of life care and pain managment; and who also is an authority on subcritical and supercritical CO2 extracts, this difference (even as a major component) will give us reason for pause when deciding on the use of one product above the other. She indicates in her courses that it would be better to use the steam distilled product in cases of itching because of the high menthol content. However, in cases of pain management, because of the higher levels of β-caryophyllene, the select supercritical CO2 product would be preferred.

Furthermore, because of the more refreshing odor profile of the select supercritical CO2 extract, its use in mental and emotional aromatherapy work would be much more desirable.

If we take a moment to examine the profiles of Ginger total supercritical CO2 extract or Black Pepper select or total supercritical CO2 extract, we find components that will need extra caution — components such as higher piperine content in the case of Black Pepper; and the ginegerols and shogaols in the case of Ginger. Therapeutically, these two products alone would be used very differently than would their steam or hydro distilled counterparts.

In addition to the change in therapeutic use itself, is the need for precision when taking client notes. Many doctors use SOAP (subjective, objective, assessment, and plan) notes when taking client notes. Many practitioners in aromatherapy and in herbalism tend to use this note structure or some other note-taking structure. The reason for the use of SOAP notes is so that if the aromatherapy or herbal practitioner needs to work in coordination with the medical doctor, there is a common language that is being spoken.

In the SOAP notes (or other note system) it is imperative that precision be recorded. This is firstly for the practitioners to understand what product was used in treatment. It is important to note if the product was an absolute, an essential oil (steam or hydro distilled), a subcritical CO2 extract, a select supercritical CO2 extract, a total supercritical CO2 extract, or even a florasol extract. The differences in the products can be integral in pinpointing any issues that might arise in the therapeutic use of these products — i.e., adverse reactions, etc. Secondly, sharing this information with medical doctors can also be helpful. Being as precise as possible can make all the difference in the world in some cases, and even can lead us to choosing a more appropriate product. If we do not make the delineation between the products in our notes (simply calling them essential oils), then we cannot make better decisions in client care when referring back to our notes.


Generalization Is Rarely Helpful….and is Anti-Science

The author of the book asserts that it would be easier and less confusing to simply classify supercritical CO2 extractions (particularly select supercritical CO2 extractions) as “essential oils.” Because of their similarities to the steam or hydro distilled products — particularly with respect to the major volatiles — he contends that the two products are essentially the same, and delineation is simply “semantics.” But, for the very reasons previously stated, semantics in this case are important.

It is rarely helpful to generalize, especially when it comes to therapeutics. In some cases select supercritical CO2 products are so similar that they and their steam or hydro distilled counterparts are used exactly the same way. But in other cases, as stated above, they are very different. So, to classify all select supercritical CO2 products into the same category generalizes to the point of indistinction, causing confusion with the plethora of products that are not quite as similar. Furthermore, the author of the book titles the book “Supercritical Essential Oils”, generalizing total supercritical CO2 extracts which are more often than not far different than select supercritical CO2 extract, and even far more different than total supercritical extracts, into the “essential oil” category. This can be dangerous, especially where therapeutics are concerned.

The book author also argues that “science” should be followed rather than established definitions — that definitions must change with science. This is very true. However, science almost never pushes the specific into the general. To do so is actually “anti-science.” Scientific method does not follow specific to general, but rather general to specific. Science is known for “digging into things” not “digging out of them.”

For those that are familiar with herbalism, what the book author is trying to do with the erasure of delineation by generally classifying all plant extracts used in aromatherapy as “essential oils” is equivalent to classifying all plant extracts used in herbalism as “tinctures.” By the author’s definition, a “tincture” would not only include pure alcohol extracts or aqueous-alcohol extracts, water extracts (infusions and decoctions), acetic extracts, and glycerine extracts, but would also generalize extraction methods within those very categories. For instance, pure alcohol or aqueous-alcohol extraction methods such as maceration, percolation, fluid extracts, and soxhlet extracts would be generalized into the simple “tincture” category. The problems with this is dosing. Each of these extracts may — and often do — require different dosing because some are more concentrated than others.

So, the idea of putting all plant extracts used in aromatherapy into the general box of “essential oils” is unfounded.


In Conclusion

Although the author of the book in question might mean well by attempting to generalize plant extracts utilized in aromatherapy as “essential oils” it is a misguided effort; for all the reasons stated above show the folly and even the dangers of doing so. These are the reasons why the ISO definition of “essential oil” has not been updated to include any supercritical (or even subcritical or florasol) CO2 products. The delineation among the products is necessary and useful; if it was not, the definition would have been updated long ago.

Aromatherapy has its own language. This language has been established for years. When changes need to be made, they are often made, but changes are never made without considerable thought; and those changes must be agreed upon the the aromatherapy community, not as a result of the preference of one.


Thank you again to Ken Miller of WholeAroma, LLC for his excellent article on supercritical CO2 extracts. If you haven't yet, be sure to follow Ken on Facebook!

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