A wine connoisseur may be able to name the grape in their wine based on how “horse sweaty” it smells, while some coffee fanatics can sniff out a bean by the level of “cardboard” in its aroma, but how much can smell tell us about different cannabis strains? For instance, is it possible to determine the strength of a particular plant from its scent, and can individual cultivars be identified purely by their aroma?
The first thing to mention is that the pungency of a marijuana plant has nothing to do with its THC concentration, as cannabinoids are nonvolatile compounds, meaning they don’t readily vaporise in the air and are therefore odourless. Even sniffer dogs can’t smell THC, and are instead trained to identify cannabis by detecting a terpene called caryophyllene oxide.
Despite THC’s lack of smell, there are plenty of other compounds in cannabis that are highly fragrant. In general, the aroma of a plant is believed to depend on its terpene composition, although research has shown that other types of volatile compounds – some of which are present in tiny amounts – can often have a massive influence on the overall odour of a plant. One study found that the ingredient with the biggest impact on cannabis aroma is actually a benzene called benzaldehyde[i], which is much less abundant than many terpenes, and which, incidentally, is the principal ingredient in almond-flavoured extracts commonly used in baking.
Back to getting baked, though, it is often claimed that Sativa and Indica strains can be distinguished between based on their general aroma, with Sativa types said to possess a sweet and spicy fragrance while Indica varieties have been described as “acrid-smelling”[ii]. One of the early studies into cannabis aromas also found that strains with high concentrations of monoterpenes (which, for the chemistry buffs, contain two isoprene units) tend to be rated as significantly more pleasant smelling than those with high concentrations of sesquiterpenes (which have three isoprene units)[iii].
Yet none of this is particularly useful to commercial cannabis producers or dispensaries, some of whom are now attempting to create marijuana ‘aroma wheels’ – like those used in relation to wine and coffee – that categorise the aromatic properties of each strain using standardised descriptions. A team of researchers even conducted a study to test whether this could be done, and found that a select number of adjectives can be used to reliably describe the aroma profile of individual strains[iv].
To conduct their research, the study authors first compiled a list of the 48 most frequently-used descriptor words found in online forums to depict cannabis aromas. This included terms like “diesel”, “cheese”, “woody”, “tar”, “skunk”, “herbal” and “earthy”. They then recruited 61 volunteers and asked them to apply these terms to eleven different cannabis strains.
The cultivars used in this study were: Alien Dawg, Durban Poison, Fruity Pebbles, G13, Jilly Bean, Lamb’s Breath, Lemon Diesel, Mob Boss, OG Kush, Snoop OG and Super Skunk. The study authors say these strains were chosen as they “span the olfactory gamut,” meaning that between them they contain the full range of smells found in cannabis.
Results showed that each strain has a distinctive aroma profile, which can be reliably described using the descriptor terms provided by the researchers. For example, the principal flavour of OG Kush was found to be “earthy”, followed by “herbal”, “woody”, “flowery”, “sage” and “nutty”. Durban Poison, meanwhile, was characterised as “citrus”, “lemon”, “sweet”, “pungent”, “lime” and “diesel”.
Perhaps the most intriguing finding from this study, however, was that all strains tended to fall into one of two distinct groups based on aroma similarity, with half being categorised as “earthy”, “woody” and “herbal”, while the other half were described as “citrus”, “lemon”, “sweet” and “pungent”.
On the whole, study participants rated the strains in the “citrus” group as being higher quality, and correctly guessed that these cultivars tended to sell for higher prices than those in the “earthy” group. Based purely on smell, participants also believed that samples in the “citrus” group had higher THC concentrations, although this estimation often proved to be wide of the mark – something that shouldn’t come as a surprise, given the lack of odour produced by cannabinoids.
Regardless, there’s clearly a lot you can tell about which strain you are smoking if you train your nose to recognise the various different cannabis aromas.
[i] Rice S, Koziel JA. Characterizing the smell of marijuana by odor impact of volatile compounds: An application of simultaneous chemical and sensory analysis. PloS one. 2015 Dec 10;10(12):e0144160. – https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0144160
[ii] Clarke RC, Merlin MD. Cannabis: Evolution and Ethnobotany. 1st ed. Berkeley: University of California Press; 2013
[iii] Mediavilla V, Steinemann S. Essential oil of Cannabis sativa L. strains. J. Int. Hemp Assoc. 1997;4:80-2. – http://www.internationalhempassociation.org/jiha/jiha4208.html
[iv] Gilbert AN, DiVerdi JA. Consumer perceptions of strain differences in Cannabis aroma. PloS one. 2018 Feb 5;13(2):e0192247. – https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0192247