These reflections are shared as a window into my approach to essential oils as a natural perfumer.
The beauty, complexity and uniqueness of the ingredients of natural perfumery is that they are alive. This very simple fact, rarely discussed, is for me one of the important joys and source of the sense of awe that my work offers.
The raw materials grow in nature. After distillation, they slowly, but constantly, evolve. When produced with care (see below for details), they have a singular identity and there is virtually an infinity of unique olfactive profile for each generic "substance" (oud, rose, sandalwood, etc). They are often composed of hundreds of fragrant molecules, which make them particularly interesting, but also delicate to work with.
For natural ingredients, the steps between the raw material and the final outcome are very few and completely transparent, for example: you take a sandalwood log, you grind it to powder, you add water and you distillate it. Et voilà. No tampering, chemical additives or filtering, solvents, rectification, etc.
As a result, natural ingredients keep many distincitve features of their source material (roots, barks, flowers, herbs, resins, etc), and some of the latter's medicinal and energetical properties will be present in the final essential oil, often concentrated. Natural ingredients act on you in a myriad of ways, beyond olfactive delight.
The so called “luxury” perfume industry (read instead : “industrially produced, with the overwhelming majority the costs used for marketing an idea of luxury, not for the contents of the perfumes”) has no understanding of whatsoever of such things. Their objectives are homogeneity and reproducibility over huge scales of production (and over years, and much more for star perfumes).
The vast majority of ingredients used are lab generated synthetics (despite marketing claims of recent time re-valorizing the use of “naturals” after a century of trying to de-class them). They are are comparatively inert and always identical. They are also much simpler, isolating different fragrant components into the smallest possible units (hence the claim of artistry when combining them). When naturals are used, they are highly transformed / rectified for homogeneity. Additives are added for stability (the opposite of curing), etc. I will write in more detail about that on occasion, as there is much more to say about such an approach, and the associated ideological machine. Industrial perfumes are not interesting to age or cure.
Industrial perfume billboard made with AI Generator evoking the all-marketing industrial reproductibility approach of the so called "luxury perfume industry". That this one is a bit corny, adds to the feel.
Natural perfumers have a totally different approach, as our working materials are singular and consist mostly of single batches with distinctive features, that will depend on many factors: crucially the terroir (especially for slow growing aromatics), the climatic conditions of a specific year (for yearly harvested ones, just like for any wine millésime) and of course, the quality of the different stages of the process from the field or forest, to the still to the final bottle. More on this below.
A quick way to resume things would be to extend the wine metaphor. Essential Oils age like wines. Good ones, well kept, will age well and even bonify with age, sometimes to amazing outcomes. And also each batch of production will have differences, in addition to their “air de famille” too. Poor quality ones will not age well at all, they will sharply decline and turn stale / to “vinegar” relatively quickly.
Ok, so essential oils age like wine. Is that all there is to it ?
Well, yes and no. In broad strokes, it is correct. Beyond that, of course, like all metaphors, this one has its limits and if you stretch it, it will become erroneous: wines are fermented, essential oils expressed, extracted or distilled, wines include tannins and skins, essential oils have organic material from the plant filtered out if any passes down the distillation, apparatus, etc. I could have used quality rums or whiskies too for different part of the analogy (as they are distilled and as a curing process often precede their selling), but the metaphors would have different limits. Also, aging wines is something more people are familiar with and attempt themselves.
Before we dive deeper, there is a few erroneous assumptions that I encounter frequently that needs dispelling. One is the strict vision that one shouldn’t age essential oils. This is actually - mostly - true from a strict healing aromatherapy point of view (more on this below) but totally irrelevant, and even counterproductive, for natural perfumery. Almost no oil for is better for natural perfumery when freshly distilled, a minimum of curing is necessary. Personally, I rarely find an oil interesting enough before 6 months to a year of curing, even for oils having the reputation of a short shelf life.
In the Middle East, and in Asia, where there are long and inspiring mutli secular traditions of natural perfumery, I often encounter the exact opposite idea and many people, even professionals, think that all oils simply get better with age. Again, there is a kernel of truth in that (many do, if the conditions are there, though to different extents depending on the kind of oil, and it is also true for their attars, perhaps to a greater extent), but there are many limits. All oils will have a turning point (even if multiple decades or beyond for some) and many oils will actually age badly.
Finally, many people, when they start discovering the world of essential oils, have simply no notion of them ageing or being affected by time and environment. They are approached a bit like inanimate objects. This is just part of the learning process, and this assumption will eventually dissolve by itself, either because some of their oils go bad, or because of studying / interacting around the matter.
What makes a good oil, then, with an interesting potential for curing / aging ?
Of course, every raw material differs in its specificity and singularity, in its terroir, that is its natural growing conditions or context and methods of cultivation, in the preparation process before distillation and in what it calls for while distilling (and there can be different options there), but beyond all these wonderful specificities, some common traits emerge.
There are general rules but they are only approximate, so it is actually necessary to progressively get to know your materials one by one, and how you like them to age. For example of general rules, (good) Oud and Sandalwood are amazing for aging and will bonify over decades if well cured, while some others oils will be much more fragile: florals can actually age much longer than one gets credit for but with tremendous variability, while essential oils that are expressed ( = cold pressed instead of distilled*) have in general the shortest shelf life (due to the difficulty of fully filtering orgnaic material and the rapid degradation of some of their core terpenes, namely limonenes)
cold pressing is used almost exclusively for the production of different (but by far not all) essential oils from fruits of the (vast) citrus family. This method refers to any physical process during which the essential oil glands in the peel and cuticles are broken in order for the oil to be released and separated from other materials.
To get a quality oil, fit for optimal curing, the first and arguably crucial factor is the quality of the raw material itself. Its intrinsic qualities of course, but also the handling and prepping before distillation, which can take many forms, and where many things can go wrong. Is the agarwood fully cleaned of white wood or not ? Is the sandalwood old enough to have generated enough oil to become interesting ? Are the rose bushes mature and untreated ? How are the flowers handled in the crucial gap between being plucked and being distilled ? How long before they are distilled ? Etc.
Then comes, the other crucial factor: the production of the essential oil itself.
Essential oils are composite mixtures of volatile compounds (usually) present at low concentrations in plants. Different extraction techniques are widely employed for the extraction of pure essential oils : cold press extraction, hydro distillation or steam distillation being the most frequent ones. Solvent extraction is also abundantly used, but it gives absolutes, which have different properties than essential oils, and which I find much less interesting for my work. For different reasons, alternative methods of extraction have been developed recently: supercritical fluid extraction, microwave or ultrasound assisted extractions are examples of new methods that can enhance yields, and provide different qualities of oils (interesting ones in the case of Co2 extraction, for example). I work mostly with traditional methods, and for the sake of simplicity, I will only focus on the importance of distillation here.
A fast distillation process will extract the more volatile components of the oil. In some cases, it might add up to a high total of all that it is possible to extract (say 80-90%). But in any case, it is the least volatile components which will only be extracted later on that will have the most distinctive and profound impact on creating the singularity and excellence of an oil.
Without them, an oil will feel shallow, hollow and diaphanous to an extent. It typically gives the kind of underwhelming impression that one has when smelling, say, an industrial rose versus a quality artisan one.
For commercial purposes, of course, it doesn't pay to extend distillations. It is a purely economic reasoning: fuel and labour forces (and other hidden costs) are expensive so why cook florals for example for hours and hours with a slow low pressure method, when it can be done in 15-20 minutes at high pressure / temperature ? Why distill sandalwood or agarwood / oud over a week or more when it can be done in a few hours. The extra investment wouldn’t be profitable for the large scale market : cost are rationalized and squeezed, like almost everywhere nowadays. End of story.
Low pressure slow distillation of agarwood over 6 days
100 degrees celsius continuously (24hrs / day)
Slow disitillation of (old) Sandalwood takes up to 10 days with the same parameters
But in our work as real artisans, it is crucial to allow the raw materials / plants to express their volatile compounds as completely as possible in the final oil: so not just only to take the superficial bulk of it, but also the finer and deeper expressions of the plant, and the less volatile compounds. Such oils have much more depth, singularity and complexity (= their own distinctive profile versus a generic one). They will also age incommensurably better. And will be infinitely more interesting to work with for natural perfumery creation. This said they will also require more care and skill for harmonious perfume composition : one cannot work with general formulas; it is necessary to compose with each singularities, which is what I love perhaps the most about my work, and what the industrial perfumers completely misunderstand in their simplistic approach to natural ingredients.
Also, on dimensions that are a bit more ethereal (and that not everyone relates to), they will give much more access to the plants “spirit”, for more subtle purposes, and will have a totally different energy to them. This is the reason absolutes feel utterly “dead” to me and one of the reasons why I don’t like to use them in my personal creations, as mentioned above.
If we were to resume the essence of this section, it would be as simple as “The higher the quality of an oil, the better the aging (in general)”
For example a low quality sandalwood oil quickly distilled from young wood won't age to magically give you a diamond : It will simply become an aged low quality oil. While in case of Sandalwood it is almost guaranteed to be more interesting than the younger oil, the oil is not necessarily worth curing, and might be better used young for its other properties (eg : cosmetic)
Experience is the most useful tool to know which oils are genuinely aging-worthy. I recommend making your own experimentations, keeping some oils for aging and witnessing the processes for yourself.
How then are essential oils best kept / cured?
Before dwelling into the “how” we need to pause briefly to sketch out what is happening with your oils (and attars) as they age. The main factor to take into consideration is that essential oils, as mentioned several times above are made up of volatile organic compounds.
These chemicals constituent are affected by time and different factors in their environment. The term “volatile” means such compounds are unstable and either evaporate easily or react quickly when exposed to other compounds.
When trying to picture essential oils aging (or transforming beyond safe use for aromatherapy healing, hence “expiring” for such uses), you need to take different processes into account. First there is evaporation means the oils’ chemicals turn into gas and escape. Some compounds evaporate more quickly than others, affecting the chemical composition (hence the olfactive profile, but also the therapeutic effects of the oil). Heat is one major cause for evaporation and it is why oils, perfumes evaporate much when applied on skin (body heat) versus, say, on a perfumer’s strip.
Oxidation is the well known chemical reaction that occurs when a substance comes into contact with oxygen (eg. Bananas getting brown). Essential oils constituents slowly break down and transform into something else as they’re exposed to oxygen. And what they become depends on several factors, like the constituent itself and the amount of oxidation it’s undergone over time. Predicting with precision how the essential oil will evolve is impossible, and this is then problematic for aromatherapy as neither the safety nor the efficiency of the oil can be properly determined once it significantly starts breaking down in such ways (which takes anywhere form a couple of years for the most fragile ones to a decade, or more for the more robust ones, like patchouli). So it is basically a “safety first” approach, so the oils used by aromatherapist remain close to what has been clinically studied.
From what precedes, if the intended use for your oils is aromatherapy healing that gets into direct contact with the body (there is also subtle aromatherapy work that happens only through olfaction), then you need to research the “official aging times” for your oils and take them seriously into account. As you do this, you will probably witness that different sources give different figures (some sources might have associated agendas to sell more product, too). Personally, as in all things, beyond those “shelf life charts” I do trust my nose and overall feeling first and foremost for this, but I have been working with oils for decades, and I don’t offer aromatherapy as a service, I only use it for myself, so if I use oils that are beyond official shelf life, which I do to different extents and degrees, I don’t make anyone else than me risk anything.
Oils destined for aromatherapy healing can't be aged like thoseused for natural perfumery
For natural perfumery and olfactive delights, all this is irrelevant. An oil is alive and interesting as long as your nose tell you that it is. But to make sure this process unfolds optimally, a few practical guidelines have to be respected.
Now we can get to the practicalities of aging oils
Especially with very expensive oils, like good ouds or sandalwoods, some people use different methods to try prevent oils from aging: provoke an air void, sometimes filling the “headspace” (the volume of air contained in the bottles) with argon gas or other gases, etc. While I understand such steps for say, a scientific scent archive aimed to last beyond one lifetime, I do not use such techniques. I love the fact oils are alive, and I love to enjoy and study them as they age. And if/when one day they are “gone”, so be it: after all, it is the fate that awaits everything in the universe, us included.
For curing, I prefer glass, and perfumer’s bottles: with very tight closing caps and a kind of septum made of silicone (so oils never touch any plastic or aluminium etc). I try to be mindful of the “headspace” as it considerably accelerates aging. I don’t mind a little bit of it but if it becomes substantial, then I decant into smaller bottles. I sometimes keep a “witness” tiny quantity with huge headpsace, just to witness and study what a lot of oxidization provokes. Of course I keep the bottles in the dark, with quite consistent temperature all year round. For the long-term curing, I use UV shielding glass (though no glass with any degree of transparency does fully shield from UV) while for sample and everyday use bottles, I prefer clear glass, as observing the “robe” (the colour and texture of the oil) is important and interesting for me. I keep such smaller bottles strictly in the dark when not in use.
Henri-Julien Dumont
In broader terms, here are the most important general points and recommendations for curing oils and attars:
- Use good bottles, glass is recommended. Make sure their caps are well designed and close very tightly, not letting air in or out. The more opaque the glass, the better protection it offers.
- Avoid any long time contact with plastics or aluminium, even in the cap or applicator.
- Always close your bottles tightly after use (it also avoids spillage accidents)
- Decant oils into smaller containers when there starts to be too much headspace, otherwise the quantity of air trapped into the bottle will accelerate oxidation (to a great extent if only a proportionally small quantity of oil remains in a bottle)
- Keep your bottles away form heat sources and from light sources. Sunlight is lethal to oils. Store in the dark when not using them.
- Avoid storing oils close to wifi routers or relays (and other appliances directly emitting high frequency waves, or xray machines, etc.). A couple of meters of your wifi boxes at the very least for long term storage.
- Avoid contamination with extraneous materials, especially organic ones (that can “kill” an oil quite quickly). If you are using oils with applicators directly on the body, those are not bottles for curing but only for regular use with a relatively quick turnover. Also make sure you are not sweating, or wearing any cream / perfume on the zone of application, because some will find its way in your bottle (alongside with a few dead skin cells), at times with dramatic consequences.
Note: aluminium is often used for the shipping and selling of wholesale quantities of oils, as it is much lighter than glass, thus diminishing shipping costs, and also much less breakable than glass. If your oils are tested to react well to aluminium - that is not react at all (and/or with the coating lining some aluminium bottles) there is no problem with it. There is no way to be sure of how an oil reacts to aluminium, according my supplier of high-end bottles in Grasse, who recommends testing each batch (so precautions much beyond each “type” of oil. They might say that to cover themselves legally in case of problems, though, but the spirit makes sense.)
What happens as oils age ?
So, in short: their chemical compositions slowly transforms. While this is problematic for aromatherapy, it is a blessing for the natural perfumer, because, very often, from that perspective good oils become much more interesting with time.
I have conducted a little test since approximately ten years: sharing both relatively “young” (1 to 3 years) and “old” (5 years or more) Rosa damascena essential oils with friends, fellow perfumers and also prospective professional clients. With a remarkable consistency, aromatherapists and healers prefer / choose the younger one, while perfumers choose the older one. It is true that such playful testing is not always blind (aka people often know which oil is which and therefore their representations of what is “right” or “best” will influence their judgment) but it also often is. There remains no doubt that perfumers, with information or blindly, almost always choose the older oil, and explain (as we lot love to do) their choices with elaborate descriptions of all the extra notes they find in the cured oil. While aromatherapists (and other healers who enjoy our rose) usually explain their preference with the “effect” and “verdancy” of the oil, so more an assessment more based on energy than olfaction. Both appreciations make complete sense for the purported context of use of the oils.
In more pragmatic terms, what happens as oils and attars age:
- the smell of the oil change over time, for good oils well kept, adding complexity and new notes to the original olfactive profile
- The “verdancy” of the oil tend to decrease, but oils can remain energetically active for a very long time, though slowly losing potency with time. For the sake of simplicity, the energy effect is what you “feel” when smelling an oil... that is not olfactive; the kind of effect it has on you (energizing, soothing, activating this or that within, etc). Different people are differently tuned to that. Some are very sensitive while some are much less, and some others will try all their might to argue in order to deny such a dimension even exists ( I think there are conditioned against it in principle, largely due to the many woo-woo uses of the word/concept of energy, and to the extravagant claims that surround them. While there are often good reasons to be put-off, such an approach is throwing away blindly the baby with the bathwater, as we say in French)
- the colour of the robe evolves (usually gets darker)
- the consistency of the oil might evolve (can be unnoticeable for a long time), due to evaprotation (oils get thicker) or degradation (they might in such case get lighter)
At some point, but surprising long compared to the “official life charts” an oil will loose its interest, it is a process that goes in degrees and those thresholds are largely subjective (like with wines, actually), so it is up to you to determine the points of no return.
L'Horloge de Flora (Roman Goddess of Flowers)
When is an oil “dead” to you ? Olfactively, when I find it has gone beyond being interesting for composition or any of the direct uses I might make of the oil. Energetically, when I don’t feel any effect, obvious or subtle, anymore. As a study object, virtually never (though of course I do dispose of stuff at time).
If I was to resume the most generic form of cycle: after and oil is distilled, it is transforming steadily and quite rapidly (top notes evolve, it morphs from being a bit diaphanous to being full bodied etc.) until it reach a first stage of maturity where it gets some stability. This is the stage where I consider an oil starts to bet interesting, for use on its own or for blending. This stage is still encompassed within the “aromatherapy use shelf life” window, and largely so. The time requires to reach this stage varies a lot between different oils. For oud or sandalwood it is at least one year, sometimes quite more, for rose at least 6 months (though I prefer a year). A citrus cold extracted oil needs less, a couple of months, etc.
Beyond this stage, the aging part of curing properly starts. There is maturation during peak years, where the oils gains in “nobility”, and complexity of its olfactive profile, without degrading in any way. Then starts a slow (always relative to the actual substance) decline with occasional thresholds … until the oil loses interest for you, other than as study material. I have had oils last surpisingly long with a fully interesting presence, if compared to the official “shelf life” charts, and amazingly interesting: 15 years old lavender, 20 years old rose, 50 years old sandalwood (the longest so far I have cured one fully myself is 30 years), etc. But I have had other oils fade away much more quickly. Those are almost always correlated to the quality factor, when compared with other oils from the same – part of – plant. It self evident, as the least volatile compounds, that will degrade the slowest, are the ones that distillations made for productivity completely miss, as mentioned above.
In short each bottle contains its own intrinsic truth, and that truth is revelead with time, in interaction with your own nose and criterions.
And this is one of the great pleasures of curing oils. Your nose witnesses the present of an oil, but with experience it also but becomes able to imagine the future. It is true for single oils, but also for an attar / pure perfume.”
And what of Attars?
Attars age in the same ways than oils, for the same reasons, and need the same care described above to age well. One distinctive factor, is that attars, when aging, increase in “unity”, and at times, it can become – even more – difficult to single out some of the separate components while smelling them. I find that most quality pure attars age amazingly well.
