What Causes Marijuana’s Pungent “Skunk” Aroma? (Note: No terpenes)

When smelling marijuana, many individual aroma notes can be perceived, ranging from floral to fruity or earthy. We all have our preferences, but one thing most smokers agree on is that any weed worth talking about should smell pungent. It should smell strongly and distinctly of weed, no matter what subtler accents are present.

Blue Dream, White Widow, and Gelato can be olfactorily distinguished by a seasoned observer, but it’s their common core smell—the smell of weed—that we want to explain. What exactly is that pungent “weed smell” common to carefully grown strains? Where does it come from? Is it based on a high terpene content or on a specific constellation of terpenes? Or is there something else?

Skunk, gas, and the perception of “good weed”

We can endlessly debate what “good weed” should smell like, but any casual smoker can tell you what it shouldn’t smell like. Good grass is always fresh grass, never old grass. Its initially pungent scent quickly loses strength as it lingers. Within a few days, that pungency fades and morphs into something far more subtle that smells more and more like hay or dried lawn grass over time. Marijuana’s pungency is also commonly regarded as an indicator of its potency – fresh, well-cured bud not only smells different, it tastes and feels better too.

Often described with words like ‘skunky’ or ‘gassy’, this pungent cannabis aroma is particularly popular with seasoned users. It’s also recognized (and often shunned) by non-consumers. Walking through the park, anyone can smell that distinctive skunk smell, which can last a long time and spread an impressive distance. And sometimes it really smells like skunk.

Terpenes are not the answer

Terpenes are a major class of aromatic compounds found in the essential oil of cannabis plants and are generally considered to be the main drivers of aroma. They’re definitely a core component, but just knowing terpene profiles alone hasn’t been able to conclusively explain people’s olfactory perception of weed. First off, not a single cannabis terpene has that pungent weed smell. Myrcene is earthy, limonene is citrusy, pinene smells like pine. Nobody smells smelly. The typical explanation for this is that the sense of smell is complicated, and the pungent weed smell must come from a complex bouquet of “collaborating” terpenes.

This explanation is not absurd, but I can tell you from several years in the cannabis industry that several groups have attempted to correlate people’s sensory perceptions (the way they say different strains smell) with terpene profiles, however, this largely failed. People don’t always describe terpene profile A as gassy and terpene profile B as fruity. Despite this, they often agree that Strain A and Strain B both taste stronger than Strain C, even though the terpene profiles of each strain differ.

An alternative explanation could be that the pungent, skunky aroma does not come from terpenes, but from another class of volatile compounds that cannabis could produce.

Chemical basis of pungent odors in nature: skunks and garlic

Instead of starting with cannabis and trying to explain its pungent aroma in terms of volatile compounds we already know exist, perhaps we should instead identify other areas in nature where this type of aroma occurs, ask, what compounds produce it, and then look for similar things in cannabis.

Skunks are notorious for the pungent odor of the aerosol spray they use to defend themselves. We simply call this smell “Skunk” and it is reminiscent of the pungent aroma commonly associated with cannabis. This odor is largely due to something called Volatile Sulfur Compounds (VSCs), which are very volatile and extremely potent—tiny amounts can be detected by the nose.

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Volatile sulfur compounds also underlie the pungent aroma of plants like hops and garlic. What about cannabis? Does it produce volatile sulfur compounds similar to those found elsewhere in nature?

Volatile sulfur compounds and the aroma of grass

I recently met with Dr. Iain Oswald, a chemist at Abstrax Tech who led a study investigating the origins of the Skunk aroma in cannabis. Using highly sensitive analytical chemistry methods, they identified several volatile sulfur compounds in cannabis. These included some that had not previously been identified in nature, as well as one that is nearly identical in chemical structure to an important VSC found in skunk aerosols.

Blends of these cannabis VSCs were able to mimic the smell of cannabis flowers. The concentration of these cannabis VSCs varied dramatically between different cannabis strains. Even more interesting: VSC concentrations correlated strongly with human olfactory perception. Participants were asked to rate the pungency of thirteen different cannabis samples. Not only did people tend to rate the samples similarly in terms of overall hotness, but these ratings were also very predictive of VSC content. The higher the VSC level, the more pungent the perceived weed aroma.

Which cannabis strains have the highest VSC levels?

In Dr. In Oswald’s study, some strains had high VSC levels while others had little to none. High VSC strains, also considered the hottest, included various Gelato and OG strains. In contrast, Goudaberry and Black Jack had no detectable VSC levels and were rated the least pungent.

Although VSCs are a separate class of chemical compounds from terpenes, VSC levels appear to correlate with terpene profiles. At a recent meeting at the American Chemical Society’s annual conference, Dr. Oswald combined his team’s data on cannabis VSCs with a study Leafly conducted in collaboration with the University of Colorado, in which we analyzed terpene profiles from tens of thousands of samples.

In our study, we identified three major “superfamilies” of high-THC cannabis strains that were categorized based on their terpene profiles. One of these families, characterized by being high in terpinolene, also tends to be low in VSC. This includes many “Sativa” strains, including “Jack” strains (e.g. Jack Herer, Black Jack), “Golden” strains (e.g. Golden Goat, Golden Pineapple), as well as Lemon Haze and Super Lemon Haze .

Most commercial cannabis strains have other terpene profiles characterized by higher levels of things like β-caryophyllene and limonene. This includes everything from Gelato and GSC to GG4 and most OG strains. Strains with these terpene profiles tend to exhibit high VSC levels.

Freshness and cannabis pungency

dr Oswald’s study also found that volatile sulfur compounds found in cannabis tend to peak when cannabis buds are dried and cured, and drop off very quickly thereafter (even faster than terpene levels). This could explain why the characteristic aroma of dried cannabis fades so quickly without careful storage, and why many consumers can quickly identify freshness by smell.

Do cannabis VSCs have psychoactive effects or medicinal value?

It is currently unknown whether cannabis VSCs (volatile sulfur compounds) affect the psychoactive effects of cannabis or have any medicinal value. Because they occur in such small amounts, they were largely overlooked until recently. Determining their pharmacological properties and examining whether they contribute to the psychoactive or medicinal effects of cannabis will be an important area of ​​future research.

To learn more about the science of cannabis VSCs, check out my recent conversation with Dr. Iain Oswald to: