DEEP DIVE: What Gives Cannabis Its Aroma? New Research Shows It’s Not Just Terpenes

New research reveals the secrets behind the aroma of cannabis

Fruity. Citrus. Pine. Diesel. Skunk. Earth. Candy. Tropical fruit.

Few plants have an aromatic range quite like cannabis. And for a long time, the explanation has been fairly simple: terpenes.

Myrcene. Limonene. Caryophyllene. Linalool. Pinene.

If you’ve ever read the description of a strain, you’ve probably seen them listed alongside little explanations of the aromas they contribute. And that isn’t wrong. Terpenes are an important part of the cannabis plant’s chemistry and contribute to its aroma.

The problem is that they don’t seem to explain the whole thing.

When researchers began comparing the chemical profiles of cannabis with how different varieties were actually perceived by the human nose, a rather inconvenient detail emerged:

Cannabis with similar terpene profiles can smell very different.

And suddenly, the question became a lot more interesting.

When chemistry and the nose disagree

In a 2023 study published in ACS Omega, researchers analysed the volatile chemistry of different cannabis varieties and combined their analysis with sensory assessments.

The most common terpenes, including β-myrcene, limonene, β-caryophyllene and terpinolene, appeared in relatively similar patterns even among varieties whose aromas were perceived as distinctly different.

When the researchers instead looked at compounds present in much smaller quantities, the differences between the varieties became considerably clearer.

These included esters, alcohols, indoles and various volatile sulphur compounds.

In other words:

The compounds present in the largest quantities aren’t necessarily the ones your nose cares about the most.

And this is where we need to talk a little about how smell actually works.

A little chemistry. A whole lot of smell.

For us to smell something, molecules need to be able to leave the material, travel through the air and reach our olfactory receptors.

These substances are commonly described as volatile organic compounds, or VOCs.

Terpenes are VOCs, but VOCs encompass a much larger range of chemical compounds than terpenes alone.

And different molecules have dramatically different odour thresholds.

This means that a compound present at a very low concentration can still dominate our perception of an aroma if the human nose happens to be extremely sensitive to that particular molecule.

Put simply:

Having the most molecules doesn’t automatically mean winning the smell contest.

A chemical analysis may show large amounts of compound A and only traces of compound B. But if our odour threshold for B is extremely low, B may still be the thing that makes our brain scream:

"Yep. THAT’S what I’m smelling."

This is an important piece of the puzzle in understanding why the aromatic chemistry of cannabis has long been more difficult to explain than a simple list of its most abundant terpenes would suggest.

Okay. But why does cannabis smell like… skunk?

This is where things get really fun.

The characteristic skunky, pungent and sometimes almost fuel-like aroma of certain cannabis varieties has long been associated with terpenes.

But in 2021, researchers identified a previously unknown family of prenylated volatile sulphur compounds, abbreviated VSCs, in cannabis.

One molecule in particular stood out:

3-methyl-2-butene-1-thiol, referred to as VSC3 in the study.

Researchers were able to strongly associate it with the characteristic skunk aroma.

And if the word thiol is making your high-school chemistry lessons flicker ominously before your eyes, we can simplify things considerably:

Thiols are sulphur-containing organic compounds, and some of them are exceptionally potent odorants.

So it isn’t particularly surprising that a relatively tiny amount can leave a very large sensory footprint.

It gets even more interesting when we look at its relationship to other familiar smells.

Similar sulphur chemistry occurs in skunk spray, hops and garlic.

So cannabis’s famous “skunk” isn’t merely an imaginative strain name.

There is actual chemistry behind the association.

And the aroma changes after harvest

The researchers didn’t stop at identifying the sulphur compounds.

They also tracked how their concentrations changed during the plant’s development and after harvest.

VSC levels increased sharply during the final weeks of flowering, reached their highest levels during the curing process and then began to decline after roughly a week of storage.

This gives us a chemical explanation for something many people who have handled cannabis will already recognise on a sensory level:

The aroma isn’t static.

What you’re smelling is a chemical moment in time.

The plant’s aromatic profile continues to change through flowering, harvest, curing and storage.

Temperature, time, oxidation and the volatility of different compounds all affect which molecules are still present when you eventually open the container.

But skunk was only the beginning

As researchers continued their work, even more surprises emerged.

The 2023 study identified additional sulphur compounds associated with entirely different aromas.

A group containing what is known as the 3-mercaptohexyl functional group correlated with distinctly citrusy and tropical fruit aromas in certain varieties.

That’s interesting because aromas like these are very easily explained away with:

"It contains a lot of limonene."

Lemon → limonene.

Case closed.

Except apparently not.

Researchers found that minor, non-terpenoid compounds could be strongly associated with the particular aromatic characteristics that made certain varieties sensorially distinct.

That doesn’t mean limonene has suddenly stopped smelling citrusy.

It means that “it smells like citrus because it contains limonene” can be a very incomplete explanation.

From tropical fruit to… skatole

And now the cannabis chemistry cabinet gets even stranger.

Researchers also identified skatole, or 3-methylindole, as an important component behind the more chemical or savoury-like aroma of certain varieties.

Skatole is a fascinating compound because our perception of its smell changes dramatically depending on its concentration and the other aromatic compounds surrounding it.

At higher concentrations, it is associated with something you probably wouldn’t choose for a scented candle.

At very low concentrations, however, indolic compounds can contribute to much more complex aromatic experiences.

And that brings us to an important point.

Cannabis aroma is a cocktail, not an ingredient list

We humans like to make complex chemistry easier to understand by breaking it into neat little pieces.

Limonene = citrus.
Pinene = pine.
Linalool = floral.
Myrcene = earthy.

It’s educational and easy to remember.

But a real aroma doesn’t quite work like that.

What we perceive is the result of many molecules at once, at different concentrations and with different odour thresholds, which can also enhance, mask or alter how other components are perceived.

Think less:

"Which molecule smells like this?"

And more:

"Which chemical orchestra is making my brain experience this particular aroma?"

A single violin is still a violin. But that isn’t the same thing as hearing the entire symphony.

So, have terpenes been a lie?

No.

And it’s important not to take the research further than the researchers themselves do.

Terpenes remain central components of the volatile chemistry of cannabis and contribute to the plant’s characteristic aroma. They can also be useful for distinguishing between cannabis varieties on a broader chemical level.

What the research challenges is how much explanatory power we have given them when it comes to the specific aromas that make a variety sensorially unique.

A terpene profile and an aroma profile are not the same thing.

Or, even more simply:

We weren’t wrong about terpenes. We just thought they told more of the story than they actually did.

Why didn’t we discover this earlier?

Partly because it’s difficult to look for something when you don’t know you should be looking for it.

Many standard analyses have focused on already known and relatively abundant terpenes. Compounds present at extremely low concentrations can therefore end up far down the list, or outside the focus of the analysis altogether.

The research team behind the VSC study used, among other techniques, advanced two-dimensional gas chromatography together with mass spectrometry and sulphur chemiluminescence.

It’s about as accessible as it sounds.

In other words:

They separated an extremely complex mixture of volatile compounds and used different detection methods to identify molecules that might otherwise have drowned in the chemical noise.

As analytical methods become more sensitive, our understanding of the plant changes with them.

Not necessarily because the chemistry is new.

We’ve simply become better at seeing it.

What does this mean going forward?

This is where the research becomes bigger than the question of why one strain smells like mango while another smells like someone opened a can of petrol in a pine forest.

If specific aromas are driven by far more classes of compounds than we previously understood, that affects how cannabis can be analysed, classified and described.

It may also have implications for breeding and cultivation. If the goal is to produce a particular aromatic characteristic, selecting plants purely on the basis of high levels of a certain terpene may not be enough.

And for consumers, it mainly means that those little charts showing myrcene, limonene and caryophyllene are not a complete aromatic table of contents.

They’re a few instruments in the orchestra.

Not the whole band.

The more we learn, the stranger the plant becomes

That may be the most fascinating thing about this research.

Cannabis is one of the most culturally charged plants in the world, yet researchers are still working to answer fundamental questions about its chemistry.

Why does it smell the way it does?

Which molecules make different varieties unique?

How does its aroma change throughout the plant’s life and after harvest?

A few years ago, many of us would have answered:

Terpenes.

Today, the better answer is:

Terpenes. Sulphur compounds. Esters. Alcohols. Indoles. And probably quite a bit of chemistry we still don’t fully understand.

Which, if you ask us, makes the whole thing considerably more interesting.

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Keep going down the rabbit hole:

Aromas are volatile. How you store your material therefore matters to what happens to it over time.

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