In my blog post about naturals (Part 1), I talked briefly about distillation. Distillation is the process whereby we get nearly all of our essential oils, cold-process being the other method that is used for citrus oils. In many cases, distillation begins at the beginning and continues to the end with temperatures and timing strictly controlled for highest quality and to yield a blend of desirable constituents. Various combinations of distillation techniques may be used to adjust oils, remove undesirable components, and otherwise produce a desirable and commercial product.
In the case of the ylang ylang flower, the distillation process is interrupted at very particular times to yield different products. The distillation of ylang ylang is an example of fractional distillation. By timing the distillation carefully, four different fractions can be separately created. Generally referred to as ylang ylang extra, ylang ylang I, II and III they are quite different in fragrance with the extra being quite sweet and ethereal for perfumery while the 3rd is more suited to making soaps, the other fractions are less commonly used. Over the course of about 24 hours, distillers interrupt the process and pull off each fraction separate from the others. During the first 1 to 2 hours the essential oil is collected and separated as the ‘Extra’. Using experience, fragrance, and specific gravity measurements distillers remove the other fractions in their time. Or, distillers may simply continue the distillation uninterrupted to create the ‘complete’ which is sometimes referred to as ylang ylang VOP or Very Old Process.
So we begin to see that distillation itself may be nuanced and manipulated to produce specific results. The second case in point is molecular distillation or MD. This process uses the parent material, e.g. patchouli plant for patchouli MD oil, and low pressure to target specific constituents for removal from the essential oil. For example molecularly distilled patchouli, also called patchouli MD, has the distinctive fragrance of patchouli but may be less dark and have the iron smell removed for a smoother and more friendly essential oil (I happen to like the more challenging version). This means that when purchasing an MD essential oil the label should list the scientific name as identical to the traditional essential oil.
For the next step in the progression, we take distillation and/or extraction to a sort of logical conclusion—isolates—which may also be called essential oil fractions. We get a clue from the name, isolate–the goal is to separate, as much as possible without chemical reactions, a single aromachemical. Linalool is a very common aromachemical and has a light and familiar floral fragrance. It is a characteristic aroma of lavender flowers but is also found in basil, coriander, rosewood, and in some 200 other essential oils (Tisserand 2014). If you use fractional distillation to get your linalool you are pretty much guaranteed to get other trace elements along with the linalool, meaning you never get 100% pure linalool and the same is true of all isolates from natural material.
If you use lavender as the source your linalool will have a pretty floral scent that will smell familiar—sort of like lavender—due in part to the other lavender aromatics that are carried along. If the source is rosewood you get a beautiful linalool but with a somewhat precious wood undertone. Which is also good. What is less good, at least for my uses, is linalool from basil, but there may come a time when a perfume calls for basil-y linalool! The couple samples I have gotten have a pretty strong herbal smell and not so much of the sweet floral. Most isolates have a similar story, you may get rosy smelling geraniol from palmarosa, lemongrass, or various citruses. Or even the peachy-smelling C-14 aldehyde from castor oil! The book Essential Oil Safety by Tisserand and Young has a list of constituents like linalool with their plant(s) of origin (see references at the end of this post).
When shopping you want to know the source—information which should be a part of the description. It will be indicated by “Ex” meaning from and the source. In the case of the peach aldehyde from castor oil the vendor should have ‘ex-castor oil’ included with the specifics. A quick search of vendors of isolates shows that some will indicate the source and some do not. It is up to the perfumer to sample and determine what best fits their need and their aesthetic.
And now for something completely different—a quick lesson in chemotypes. Rosemary and basil are two familiar essential oils that have different chemotypes (CT). Basically, this means that the chemical makeup of the essential oils from plants of the same species is unique enough to give a different aroma or therapeutic effect. Rosemary comes as Rosemary CT cineole and Rosemary CT verbenone most frequently but there are others. Each has slightly different aroma, use, and safety. Chemotypes are generally the result of different growing conditions. Just as “Haute” or high elevation lavender differs from the more common mid-elevation type, so does rosemary have variations between plants and growing locations. Breeding and selection may also be used to emphasize a particular chemotype in plants that have such variation as part of their DNA. As with all essential oils, isolates, and other aromatic materials it is up to the perfumer to be educated as to safe and appropriate use.
I will continue to dip, from time to time, in issues related to natural perfumery and natural ingredients. In addition, I’m inspired to get back in the workshop with more experiments. So sign up for the newsletter and keep an eye out.
Tisserand, Robert and Rodney Young 2014. Essential Oil Safety: A guide for health care professionals 2nd Edition. Published by Elsevier.