Imagine opening a jar of dried flowers. Before you see, read or know anything, your nose has already made up its mind. Sweet tropical fruit, spicy earth, dry hay or fresh lemon. The verdict comes in milliseconds.
But what exactly creates this precise sensory picture in your brain?
For years the answer was: terpenes. The industry printed terpene profiles on labels, and consumers learned that myrcene stands for earthiness and limonene for citrus. It sounded convincing. As research now knows, it was only part of the truth. A series of groundbreaking studies has fundamentally shifted the picture: the aroma of cannabis is far more complex than previously assumed, and terpenes alone do not explain why a strain smells earthy or citrusy. What actually makes a strain smell of tropical fruit, spicy earth or fresh lemon follows a different, more fascinating logic. A logic that can only be revealed with the most advanced methods of chemical analysis.
Over 200 terpenes and hundreds of other substances
The plant Cannabis sativa L. produces an exceptionally rich spectrum of volatile compounds: more than 200 different terpenes alone have been identified so far. On top of that come hundreds of other volatile organic compounds from entirely different chemical classes, such as esters, aldehydes, ketones, alcohols and volatile sulphur compounds (VSCs).
The most abundant terpenes, including β-myrcene, α- and β-pinene, d-limonene, β-caryophyllene, terpinolene and humulene, can together make up as much as 50 % of the measured aroma concentration of a cannabis strain. That sounds like a clear statement, but it is not really one. In aroma science, the concentration of a substance and how we perceive it are two fundamentally different things. A substance present in high concentration does not necessarily shape the smell of a strain, and vice versa.
Alongside terpenes and flavonoids, volatile organic compounds such as esters, aldehydes and ketones play a decisive role in the nuanced aroma and flavour profiles of cannabis and hemp. Then there is a group of compounds that went largely unnoticed for a long time: volatile sulphur compounds (VSCs), nitrogen-containing heteroaromatics and a range of other trace molecules that aroma research groups together under the term “flavorants”. These flavorants are often exactly the molecules that give a strain its unmistakable sensory signature.
The paradigm shift: the 2023 study
Probably the most important single study on cannabis aroma in recent years was published in October 2023 in ACS Omega, the peer-reviewed journal of the American Chemical Society (1). Iain W. H. Oswald and his team analysed 31 cannabis extracts with very different aromas using two-dimensional gas chromatography combined with time-of-flight mass spectrometry and flame ionisation detection. This combination of methods makes it possible to separate and identify even the tiniest trace amounts in complex mixtures with precision. The result was surprising: strains with very different aromas showed remarkably similar terpene profiles. So terpenes contribute little to these unique, strain-typical scents. Instead, many small, non-terpenoid compounds correlated strongly with the unusual sweet or savoury aromas.
This is a fundamental finding. It means that anyone who tries to characterise a strain by its terpene profile alone is only telling part of the story. The analysis showed that even limonene, the terpene intuitively associated with citrus and fruit aromas, did not reliably predict whether a strain actually smelled of citrus. In many cases, the real carriers of these aromas were not terpenes but other trace compounds such as tropical VSCs and esters. The study identified 30 esters in cannabis alone, each with different aroma properties, including ethyl hexanoate with an apple-like scent and n-propyl hexanoate with an aroma of blackberry and pineapple. These esters have long been known as key aromas in the food and beverage industry. Their detection in cannabis opens up a completely new perspective on how strains are described.
Volatile sulphur compounds: tiny amounts, maximum impact
Volatile sulphur compounds (VSCs) hold a special place on the new aroma map of cannabis. An earlier study (2) had already identified a new family of prenylated VSCs, including 3-methyl-2-butene-1-thiol (MBT), the main chemical source of the characteristic smell of “skunk” strains (named after the animal). Prenylated VSCs such as 3-methyl-2-butene-1-thiol are mainly responsible for the pungent, skunk-like smell of cannabis. Their concentration peaks towards the end of the flowering and curing phase.
These compounds, which are structurally similar to the bioactive sulphur molecules in garlic, take effect even at the lowest concentrations. The biochemical kinship with garlic is no coincidence: it suggests that, in the course of evolution, cannabis may have developed protective mechanisms against herbivores similar to those of garlic.
The 2023 study (1) went further and identified a new class of tropical VSCs that explain the citrus and fruit aromas of certain strains. Volatile sulphur compounds with the 3-mercaptohexyl functional group are responsible for the distinct citrus aromas of certain strains. Skatole (3-methylindole), on the other hand, is the key source of the chemical, savoury aroma of other strains. Skatole is known from the perfume and food industries and smells anything but pleasant in higher concentrations. In the vanishingly small amounts found in cannabis, however, it adds a spicy, earthy depth that many consumers perceive as particularly expressive.
The key principle behind this is the odour threshold: a compound present only in the tiniest traces can dominate the smell of a compound that is a thousand times more abundant, as long as its odour threshold is low enough. Such compounds are often found at concentrations below 0.05 % of the sample mass, yet they can still make a considerable contribution to the aroma. In the course of evolution, the human nose has specialised in detecting exactly such traces: after all, a few molecules can warn of great danger or point to something enticing that matters for survival.
Terpenes and their biological effects: what research shows
Even though terpenes do not single-handedly determine the aroma diversity of cannabis, it would be wrong to play down their importance, especially with regard to their possible biological properties. New preclinical studies suggest that terpenes could be more than mere fragrances. Researchers at the University of Arizona showed that certain cannabis terpenes act in a cannabimimetic way, meaning they can produce effects similar to cannabinoids and selectively enhance their activity by directly activating the CB1 receptors of our endocannabinoid system (3).
What is remarkable: limonene, which seems to contribute little to the strain-typical citrus note as an aroma compound, nevertheless showed a measurable biological effect in a clinical study in humans (4). Combined with THC, it significantly reduced the anxiety triggered by THC in the study participants. Aroma and effect apparently do not always follow the same molecular pathways. These findings are scientifically interesting, but based on current research, no clinically confirmed conclusions about therapeutic effects can be drawn from them.
Hemp tea and other ways to enjoy: aroma as a sensory experience
Whether you vaporise a cannabis strain with THC, CBD or THCV or brew a hemp tea from a particular strain: either way, you experience the full complexity of this world of aromas in one of its most accessible forms. Heat (be it the vapour of the vaporiser or the hot water of the infusion) releases the volatile compounds from flowers, leaves and herbs. Terpenes such as linalool, pinene and myrcene reach the nose first, while earthy and floral base notes set the frame. But what gives the infusion or vapour its individual character, whether it smells fresh and citrusy, spicy and tart or deeply earthy, is largely determined, according to current research, by those small trace molecules that are so hard to measure: esters, heteroaromatics, VSCs. The human nose, equipped with more than 400 types of olfactory receptors and able to distinguish an estimated one trillion odour mixtures (12), grasps this complexity intuitively, long before analytical methods have caught up. That is one reason why experienced connoisseurs often recognise their favourites by the smell of the opened pack, before they have taken a single draw or sip.
Switzerland: regulatory leeway, aromatic diversity
One regulatory detail matters a great deal for the quality and aroma of Swiss hemp products: in Switzerland, hemp with a THC content of less than 1 % does not fall under the Narcotics Act, whereas the EU limit is 0.3 %. This threshold, more than three times higher, gives Swiss breeders and producers access to a much broader genetic range of strains. Many traditional or robust hemp strains naturally have slightly higher THC levels without having a psychoactive effect. Under the EU limit, such strains fall through the cracks. Since terpene profiles, VSCs and other aroma compounds are closely linked to a strain's genetics, more strain diversity directly means more aromatic diversity. An advantage Swiss producers have been benefiting from for years.
Outlook: the aroma map is being redrawn
Research in recent years has fundamentally changed our picture of cannabis aroma. Volatile components such as terpenes, aldehydes, ketones, esters and sulphur-containing compounds interact with non-volatile molecules such as flavonoids and phenolic compounds, and together they determine the characteristic aroma and flavour of cannabis. In practice this means: terpene profiles on product labels give you a first orientation, but they are not a reliable prediction of the actual sensory experience. Breeders, producers and consumers who want to understand the full aroma potential of cannabis will have to rely on more comprehensive analytical methods in future, and, in good old-fashioned style, on their own nose.
Whether and how the individual aromatic components (be they terpenes, VSCs or other trace compounds) modulate the effects of cannabinoids still needs further research. But what we already know is promising.
Sources
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