The aromatherapy practitioner has an array of oil choices to choose from these days. With new technologies, purchasing and blending require a little more knowledge than they used to. In addition to the classic steam distilled oils, there's several types of oils and extracts using solvents other than water. The oils produced by each method are quite unique, both aromatically and therapeutically. Here's a brief, informative guide to help understand the differences -- here between steam and CO2 distillates -- and why you might choose one type of essential over another.
The starting point for this discussion is the term "essential oil". Technically, an essential oil is produced only via steam or hydro distillation of plant material. One can imagine a large metal container holding plant material. Steam is passed through this from below (or the plant material is boiled, in the case of hydro distillation), and captured at the top of the container. When the steam cools and again becomes water, there is a layer of oil on top of it. The water is drained-off from below, leaving the essential oil.
You can then imagine that this process extracts a certain group of molecules from the plant material. With boiling water or steam as the "solvent", and the natural separation occurring at the end, this group of molecules (called the "essential oil") has the features of not being dissolve-able in water, yet is extractable with steam. If a different solvent was used, or only tepid water, this "oil" would not be the result.
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 general difference of the oils produced can be though of in this way: steam distillation captures the most volatile compounds of the plant. What makes a flower's scent is a very light alcohol-like oil evaporating from the flower -- steaming forces this from the plant, to be collected when the steam is cooled. Carbon dioxide distillation is like making tea that captures the oily components of the same plant. This includes the volatile oils, but includes other larger molecules as well that do not so easily evaporate. Steaming can change some of the natural volatile components of the plant as well, where these alterations are not made by the cooler CO2 process.
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.
In other instances, the steam distilled oil is most often the preferred one. Lavender is far more popular as a steam distillate; it's aroma is familiar and its therapeutic properties are highly valued. Blue chamomile does not turn blue unless its steam distilled (though the CO2 is also highly valued, yet thick and not as easy to work with). Patchouli is interesting as a CO2, but not widely used. This list goes on, with the important point being this: that one distillation method is not better than the other. The oils and extracts they produce are simply different. They'll have different therapeutic properties, aromas and even "energetics".
So when the question comes up, "which is the better oil?", the answer is "the best one for the job". The answer for each condition is actually usually pretty clear. An understanding of what you're needing the oil to do for you, plus a little internet research, should point you in the right direction. And if it's aroma you're looking for, what a great thing to get to sample a whole new kind of essential oil -- technology has it's benefits, and has helped us in this wonderful way.
The starting point for this discussion is the term "essential oil". Technically, an essential oil is produced only via steam or hydro distillation of plant material. One can imagine a large metal container holding plant material. Steam is passed through this from below (or the plant material is boiled, in the case of hydro distillation), and captured at the top of the container. When the steam cools and again becomes water, there is a layer of oil on top of it. The water is drained-off from below, leaving the essential oil.
You can then imagine that this process extracts a certain group of molecules from the plant material. With boiling water or steam as the "solvent", and the natural separation occurring at the end, this group of molecules (called the "essential oil") has the features of not being dissolve-able in water, yet is extractable with steam. If a different solvent was used, or only tepid water, this "oil" would not be the result.
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 general difference of the oils produced can be though of in this way: steam distillation captures the most volatile compounds of the plant. What makes a flower's scent is a very light alcohol-like oil evaporating from the flower -- steaming forces this from the plant, to be collected when the steam is cooled. Carbon dioxide distillation is like making tea that captures the oily components of the same plant. This includes the volatile oils, but includes other larger molecules as well that do not so easily evaporate. Steaming can change some of the natural volatile components of the plant as well, where these alterations are not made by the cooler CO2 process.
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.
In other instances, the steam distilled oil is most often the preferred one. Lavender is far more popular as a steam distillate; it's aroma is familiar and its therapeutic properties are highly valued. Blue chamomile does not turn blue unless its steam distilled (though the CO2 is also highly valued, yet thick and not as easy to work with). Patchouli is interesting as a CO2, but not widely used. This list goes on, with the important point being this: that one distillation method is not better than the other. The oils and extracts they produce are simply different. They'll have different therapeutic properties, aromas and even "energetics".
So when the question comes up, "which is the better oil?", the answer is "the best one for the job". The answer for each condition is actually usually pretty clear. An understanding of what you're needing the oil to do for you, plus a little internet research, should point you in the right direction. And if it's aroma you're looking for, what a great thing to get to sample a whole new kind of essential oil -- technology has it's benefits, and has helped us in this wonderful way.
About the Author:
The author is proponent of the varied and potent healing actions of aromatherapy essential oils. For more, see http://www.anandaapothecary.com/essential-oils.html.
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