subject: Practical Aromatherapy: A Look At Modern Distillation Methods [print this page] The savvy aromatherapy practitioner will find themselves with more choices to make than ever before, one of them being between carbon dioxide and steam distilled essential oils. The oils produced by these methods are significantly different, both in aroma and therapeutics. The question is often raised: "Is one better than the other"? The answer is a definite "maybe". Here's a primer on these methods of making essential oils, to help you make a more informed decision when buying essential oils for therapeutic applications.
An important piece of trivia in the world of aromatherapy is that only essential oils produced using steam or boiling water are by definition "essential oils". For the beginner, you can picture a giant pot filled with roses, with steam being ported in from the bottom and being captured by an upside-down funnel at the top. The captured steam is cooled and again becomes water; floating on top of the water is rose essential oil. A simple separation process leaves you with pure rose essential oil.
One can conceive of the various factors that produce this oil, just as if one were cooking a meal. The "solvent" being steam (or water), the temperature of the steam (or water), the time (how long steam was passed through the plant), and pressure within the distillation vessel affect the resultant product. And while the time, temperature and pressure have important implications on the quality of the essential oil this produces, in general, is a "relatively" similar chemical mixture each time it is used with a particular plant -- e.g. every steam distilled essential oil of lavender is relatively similar to every other. (If you used a solvent other than water, or cold water, your resultant product would be something other than lavender essential oil.)
Carbon dioxide distillation is more akin to making tea, then evaporating all the water. But pressurized, liquified carbon dioxide is not the same as water in an important chemical manner -- it is not polar (it does not have different electrical charges at either end of the molecule). You can imaging making a cup of peppermint tea, then evaporating all the water -- you would not be left over with essential oil. But if you do this with liquid carbon dioxide (which happens at much lower temperatures than "steaming"), and release the pressure so the CO2 again turns to a gas, you would be left something akin to peppermint essential oil...but unique in special ways.
The result of the CO2 distillation process is an oil with a greater range of molecular sizes than steam distillation produces. It's like making a tea that captures oily molecules (these can better be thought of as non-polar for the chemically-inclined) rather than ionic (polar) ones. CO2's can capture the same molecules as steam distillation plus ones that are too large and less-easily evaporated. At the same time, the steam distillation process concentrates these smaller, very volatile molecules, and actually creates some new ones. (Despite what we think of as a "pure" process, steam distilling does in fact alter some molecular structures of the plant's natural volatile oils).
There are different types of CO2 extracts available as well (aside from the super-critical and sub-critical manufacturing methods). You'll see oils labeled with either "total" or "select". By adjusting certain factors during distillation, the "select" extracts will exclude some of the largest molecules and therefore will be more similar to a steam distilled oil. The "total" extraction seeks to capture all the oily, non-polar molecules, and will be most similar to the original plant material in this way. One is not better, just different...you may find a select to be more potent aromatically, yet a total may give you aromatic (and therapeutic) nuances that would otherwise not be available.
For some plants, you'll have a selection between CO2 and steam distilled varieties. One finds that the steam distilled oils are often of higher notes, brighter and more intense. The CO2's can be warmer and more full-bodied. Though this too is still a generalization, but one that holds for the majority of essential oil varieties. Some plants are only offered as CO2's and not as steam distilled oils -- this you'll find when the concentrated plant material is thought to have significant therapeutic properties, but the volatile aromatic oil is either hard to obtain or not of significant therapeutic interest. Extracts very high in antioxidants and other therapeutic nutrients such as calendula, carrot root, sea buckthorn and whole rosehip are good examples. This, in a way, can be a guideline for selection between the two oil distillation types.
Yet as wonderful as CO2's sound, there's no substitute for most of the classic steam distilled aromatics. Lavender is just not the same as a CO2, nor Ylang Ylang or many other oils. Eucalyptus would not have its incredibly diverse effects on the immune and respiratory systems as a carbon dioxide distillation. These still hold their own as truly important therapeutic aromatics. The important point is that one method does not produce a better or more healing oil, they're simply different -- which is really wonderful as it gives the aromatherapy practitioner an even bigger palate to work with!
So you're more than likely going to come to a point when buying an oil, which is better: the steam distilled or the CO2 extract? The answer is you'll have to do a little research to figure which oil best suits your needs. It may just be the aroma you're looking for, and in that case the choice is easily made by smelling samples. In other cases, you may have to dig a little deeper...remember that neither is necessarily better -- just different -- and both can be wonderful natural medicines.
