Sandalwood, particularly Santalum album, is one of my favourite aromatics, and also the one I wear the most by quite some distance. It is a story of love, but also of constant investigation and learning.
I have been wanting to start a series on sandalwood on the Hearnotes blog for ages, but I keep collecting scientific articles and journaling experiences instead. Thus, I end up with hundreds of pages of notes piling up, always looking for new information but never taking the time to, well, distill this information.
Today a dear client asked me a question that I have been asked over and over : what is the santalol content of this oil ? While the contemporary obsession with santalols numbers often makes my eyes roll into my skull, in this instance I was actually genuinely thankful for the question. Because it came from someone I appreciate exchanging with, and appreciate as a person, and because their question unlocked my writing block by giving me the topic for the first entry for these Sandalwood chronicles.
Instead of replying with a long email, like I often do, I would write this little blog post, which I dedicate respectully to them.
Santalols do not make the soul of an oil
Quantitatively, the major constituents of sandalwood (s. album) oil are sesquiterpene alcohols, which include the famous alpha and beta santalols. Those two constitute the major proportion of an oil, generally totaling approx. 60–80% of the total oil mass (up to 90% with older modes of calculation that included all sesquiterpene alcohols, which are numbers that still circulate today and that can give a wrong idea).
Research* has shown that these constituents can show a uniform composition across samples of vastly different origin and quality, playing little role in the fragrance profile.
Conversely, minor constituents vary greatly in chemical composition and olfactory profile. These minor constituents account for a much smaller proportion of the total mass of an oil, but variations in their composition were shown to make significant changes to the aroma profile and qualitative experience of the different oils researched.
Combined α- and β-santalols make up the heavy structural body of the oil and provide its foundational texture, but not its deeper identity or soul. One could say that Santalols form the canvas (with a sketch), but not the painting. Or the beams, but not the house, and even less the home.
Whoever smelled santalol isolates will agree that they make for a flat and boring experience, very far from the deep joy of wearing a good sandalwood oil. And while isolates are what they are for a reason, they point to the crucial fact that santalols are, in fact, never isolated in a real oil.
The same research also mention experiments with an isolate of the four majour sesquiterpene alchols of Indian sandalwood oil (our two plus trans-α-z-bergamotol and epi-β-santalol), making up around 80% mass of the tested oils in total. The outcome was : "an isolate of these four molecules, while having a clear, woody lactonic odour does not have the character of a good Indian sandalwood oil, it lacks the intensity and complexity for which Indian sandalwood oil is renowned".
α- and β-santalols are nervetheless clearly key to the basics of an oil, and responsbile for the outline of its lactonic and woody facets, and of its fixative properties. For their outline, but not for the whole picture, far from it. Beyond that, they are also crucial for the many important aromatherapy properties of Sandalwood.
When a tree grows old (50 to 100+ years before harvest), its root system and heartwood accumulate a massive matrix of other compounds that can vary wildly with terroir. It is those trace compounds, when properly distilled, that will dictate the unique aromatic nuances that give an oil its soul, and distinguish true artisan works from mass-produced oils.
Bottom line : the soul of an artisan sandalwood oil lies in the minor constituents and their orchestration, not in the dominant molecules and their ratio (which of course matter too : without a canvas, there is no painting).
It is important to clarifiy that in this post, I do not dispute the importance of santalols at all, but rather put the focus on a widely spread blindspot / misunderstanding : how their numbers are so often overrated and misinterpreted nowadays.
Santalols numbers or ratios by themselves do not make the quality on an oil
Santalum album's genetic framework implies that once a tree forms mature heartwood (usually by year 25 to 30), the percentage of santalols in the distilled oil approaches their natural maximum ceiling. The exact age and values will depend on the specific tree's genetics, and its environmental growth factor. A 30-year-old plantation tree and a 60-year-old wild tree can both easily yield very similar α & β-santalol percentages and ratios.
What drastically changes, and increase, are the minor compounds described above, and the yield. A 10-year-old tree's wood might only yield 0.9% oil by weight; a 30-year-old tree might yield around 4%; while a 50+ year-old tree can yield up to 6% or 7% of dense essential oil or even more for very old trees over long distillation cycles.
More meanigfully for the fragrant profile, old wild trees that survived decades of harsh natural conditions and symbiotic root interactions with their environment develop a massive defense mechanism of complex resins. Sandalwood trees are classified as root hemiparasites, meaning they that unlike typical plants that rely solely on their root systems for nutrients, sandalwood trees have evolved a unique strategy to tap into the roots of neighboring plants to obtain water and essential minerals, which is precisely why terroir and age is so important for sandalwood, and why plantation trees will always feel lacking.
So, additional years of growth contributes to the tree developping more heartwood, more oil (so more total santalols in absolute terms, but not in their percentages of oils mass or respective ratio's terms), and, crucially, much greater minor-constituent richness, thus better aromatic richness and complexity.
Artisan distillers use slow, low-temperature hydro-distillation over very long cycles. This slow-cook method extracts out those heavy, rare, high-boiling-point trace compounds from the old wood that commercial setups miss entirely, naturally changing the total molecular ratio of the final oil.
These emerge in the Gas Chromatography report as unique trace compounds, naturally crowding out and mathematically lowering a little the overall and respective percentages of the major santalols (while still remaining the the sweet spot of numbers, just not with maxxed out values).
Counterintuitively, thus, some old-growth wood artisan distillations can actually display lower santalol percentages while smelling vastly superior to plantation oils.
Likewise, it is widely known by natural and traditional perfumers, as well as by sandalwood lovers, that good sandalwood oils benefit greatly from appopriate curing. But, with age, the santalols polymerize while the top notes mellow, creating a velvety, seamless transition from top notes to base longevity bliss. As slow polymerization, evaporation and oxidation occur, the oil becomes thicker, more resinous, and usually turns darker in color. An aged oil may actually show a slight decrease in santalols on paper due to this process, but its aroma will be vastly superior, richer, and more tenacious than a fresh oil with "perfect" numbers.
It is thus completely possible for a superb oil to fall short of mediocre ones in terms of pure santalol numbers. It is even theoritically possible for it to fall slightly outside of the ISO standard's scope that defines that an oil should comprise between 41–55% α-santalol and 16–24% β-santalol. This is a theortical possibility and in no case an argument pointing at something like "the best oils will have such weak numbers", which would be false. Also, importantly : serious discrepancies in numbers or ratios, though, are much more likely to be signs of tampering.
The bottom line: Traditional / artisan distillation maximizes the extraction of heavier sesquiterpenic lactones, resins, waxes (etc.) from the old-growth wood. These compounds can lower the percentages of santalols on a GC sheet because they take up room in the "pie chart" (relative percentages of compounds), but they massively increase the olfactory beauty, tenacity, and fixative qualities of an oil. They give it its soul.
People who misunderstand and overrate santalol percentages numbers and their relative ratios might find that an incredible oil has "disppointing numbers" and be seduced by the numbers of a mediocre one that can smell sterile and flat, because poor in those microconstituents numbers and orchestration.
In short, santalols higher numbers do not necessarily mean at all "better oil".
The ISO Standard : commercial benchmark more than quality marker
The ISO 3518 standard uses the language of quality, but it was established as a industrial benchmark for large-scale fragrance houses, cosmetic and flavor corporations. It was never conceived to identify masterfully distilled oils from terroir infused old-growth wood.
An artisan oil is a snapshot of a single tree, a specific micro-terroir, and deliberate distillation and curing choices. Global corporate buyers are after predictable uniformity and reproductibility, which makes complete sense for their goals, such as large scale perfume production or cosmetic formulas. On the other, hand rare aromatics lovers are (usually) after singularity and diversity of experiences: two very different objectives.
But both want to make sure that ther oils arent't adulterated with cheap synthetic fillers or diluted with inferior trees' species. The ISO standard can greatly help with that, and beyond the GCMS testing it relies on, which provides for that very relevant information.
This said, it is actually not that hard to fool gcms tests with adulterants for skilled counterfeiters. It would be a totally different topic to explore the adulterations methods and the other tests that could unveil them.
It is important in this regard to simply remember that adulteration can be hidden behind good-looking numbers. An oil can be engineered to present perfect santalol values while still being rectified, blended with lesser species, manipulated with isolates or bioengineered santalols, etc.
Beyond such risks, and, very importantly, provided that, first, the test results are genuine (tweaking results on reports is sadly not a rare thing, so only independent testing by a trusted lab can be considered valid), and, second, that the gmcs test was not fooled by skilled cheating, then the gcms test results are definitely useful.
The α- and β-santalol percentages and ratios, in such tests, can be regarded as necessary but not sufficient indicators. They are good for screening, for giving authenticity clues, for very basic but easily misleading grading and for comparison within well understood limits.
Proper santalol numers & ratios would indicate that the oil is indeed Santalum album and not a cheaper species and that it hasn't been heavily cut with diluents or artificially boosted with isolates. But those number and ratios cannot never prove authenticity. On the contrary, largely out of balance numbers and ratios will give more solid clues that there is a very likely problem / tampering with the oil, which is of course a crucially important outcome.
Santalols are produced in the heartwood and roots of the tree, not the sapwood. Therefore, proper santalol levels would also indicate that the wood used had a high ratio of true heartwood or root system.
While such numbers do potentially give necessary clues about authenticity and tenacity, they are not sufficient in themselves to establish anything with certainty.
More importantly for sandalwood lovers, they also mask or ignore the soul of an oil, the distillation artistry behind it, the age of the wood, the maturation of the oil, the complexity, the radiance, the olfactory experience and beauty, the evolution on skin over time, etc.
The full gcms results beyond the santalol indicators don't help much more with all that either, tough they are of course very interesting to analyze for those with the relevant skills, and will give more clues. But they are not at all easy to interpret.
The bottom line : Santalol numbers and ratios, and gcms tests have very important functions, but they are often overinterperted and misunderstood. Their main interest is to provide authenticity clues (or very strong inauthenticty ones) about an oil but they tell nothing (or very little) about the qualitative experience of a genuine oil or how it was produced.
Chasing Santalols - when industrial concerns hijacks actual quality
In the broader essential oil market, focusing strictly on hitting an ISO target for santalols has led to commercial growers harvesting trees as early as possible (sometimes at just 15 to 20 years old) because the trees have technically reached a sufficient baseline chemical maturity to meet the standard and the turn over is quicker, thus more profitable.
Furthermore, mass commercial distillers use high-pressure, "rapid" steam distillation (24h for the quickest large scale facilities) to strip the wood efficiently, thus prioritizing maximum santalol extraction to the detriment of other compounds.
While these young-harvest plantation oils combined with industrial steam distillation can yield a legal, textbook-accurate α-santalol & β-santalol profile, they often smell sharp, aggressive, single-dimensionally woody, flat, dull, heavy, thin, monotonous or even over-lactic (evoking sour dairy) or urine-like.
In any case, they will lack the multi-faceted "soul" that only time, ancient root systems intreacting with a mixed environment, a complex universe of trace compounds and skilled slow long cycle distillation (up to 10 days uninterrupted) can weave into the oil.
Quantitative simplicity
So why are santalol numbers fetishized nowdays, why is their importance so exaggerated ?
I think it is because it fits perfectly with our current society...
... They seem solid and scientific, after all they are made of hard numbers, not fluffy olfactive descriptions
... Thus, they are easy to measure, easy to compare, easy to rank and... easy to market.
A seller can say, and often will loudly claim “high santalol = superior oil,” and that will sound objective (while it is simply not true as such, as we have seen).
Thankfully, natural perfume materials can never be judged by the ratio of a couple of major molecules, the full picture is much more complex than that : in dialog with the major components that are santalols, it is the (more than) hundred other molecules and their orchestration that matters the most.
But that is much more complex and can never really be quantified, and even less so reduced simplistically, so it disappears from most discourse.
Qualitative musings
Among the many facets of a good sandalwood oil that are completely ignored by santalol numbers are, for example, the opening / top notes, the incensy facets and all other nuances of character (floral, fruits, green, spicy, leathery, animalic etc- but also the quality and feeling of the creaminess), how it evolves and transitions over time, how it behaves in a composition, etc.
A sandalwood oil fragrant experience is organic, dynamic, alive, and multidimensional. That translates in experiences of density, roundness, depth, smoothness, integration, etc.
All those nuances and experiences are richer in old growth wood properly distilled but do not translate in "higher santalols ratios".
Olfactory beauty cannot be measured, and relies more in trying to answer experiential questions.
Does the oil open beautifully ? And how, with what overtones? Does it bloom on skin? Is there radiance, or only buttery weight ? Does it feel alive or inert? How does it evolve with time ? Does it elevate you ? Does it pacify you ? Does it ground you ? Do you feel a feeling of delight or bliss ?
Taste is of course subjective : I personally enjoy terroir (complexity, harmony and unfolding of the minor consituents and the singularity of their orchestration in an oil), smooth integration, absence of harshness, or stale notes, a velvety body that shines without heaviness, a long organic drydown and, last but certainly not least : the elusive but so distinctive “sacred” or meditative depth feeling (the real bliss for me).
We live in a hurried society, that fetishizes quantification to the detriment of qualitative knowledge. I understand that (though I deeply dislike the fact). But with high quality rare aromatics, there is no shortcut, only the slow knowledge gathered with first hand experience of the materials is really meaningful, and that takes years and years if not decades to develop and a lifetime to refine.
Numbers will tell you close to nothing meaningful about a singular oil (bar the important basics covered above), while evaluating it with your nose and savoring its complex transitions over time on skin is, amusingly, far more... accurate than the picture any santalol numbers, or any gcms test results, will ever provide for understanding the olfactive profile, experience and "reach" of an oil.
Judging sandalwood oil by α- and β-santalols numbers is a bit like judging a rare vintage wine only by its alcohol percentage and ph : a narrow focus on important factors giving a very limited picture of things.
The gates to the soul of an artisan distilled, old growth wild sandalwood oil can only be your nostrils.
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* Research directly quoted :
Hettiarachchi, Dhanushka & al. Little Things Matter: Effect of Minor Constituents on Aroma Profile of Indian Sandalwood Oil . Paper presented during IFSCC Congress 2022 in London, on 20th september. Full version is easy to find online, The olfactory pyramid chart is also taken from this paper.