The Molecule Connecting Cannabis Odor and Light-Struck Beer

When plant aromas are analyzed, trace compounds can sometimes define their characteristic smell more than the most abundant substances do. The pungent, skunk-like odor of cannabis flowers is one example.

A 2021 study closely examined trace sulfur compounds and identified a central contributor. It is a molecule also known for the light-struck off-odor of beer. The researchers further investigated whether it remained in extracts and how its abundance changed during growth and storage.

A characteristic odor that terpenes alone could not explain

Cannabis aroma contains many terpenes, including myrcene, pinene, limonene, and caryophyllene. These compounds contribute to differences in woody, citrus-like, floral, and other notes.

Yet studying them had not adequately explained the source of the strong skunk-like smell. The researchers focused on volatile sulfur compounds, a class of sulfur-containing substances that enter the air and carry odors, sometimes powerfully even at low concentrations.

Their aim was to identify the compounds behind the characteristic odor and examine how they corresponded to people’s smell impressions. They also investigated whether the same compounds occurred in extract products and how their levels changed from growth through postharvest processing.

Two stages of separation and a sulfur-sensitive detector

In a complex aroma mixture, a trace compound can remain hidden beneath other peaks when the mixture is separated only once. The study used comprehensive two-dimensional gas chromatography, combining two separation columns with different properties.

The researchers also combined a mass spectrometer for molecular identification, a detector for quantification, and a detector sensitive to sulfur-containing compounds. Separate sample-preparation approaches were used to capture abundant aroma compounds and trace sulfur compounds.

The comparison included 13 samples from multiple varieties. Among them were two samples from the same Gelato batch measured after different storage periods. Four trained assessors, blinded to sample names, rated the characteristic pungent odor on a scale from 0 to 10.

The analysis revealed a family of sulfur compounds sharing a carbon framework known as a prenyl group. The paper labeled them VSC3 through VSC7 and confirmed each against reference standards.

The key molecule is also known from light-struck beer

The central compound, VSC3, was 3-methyl-2-butene-1-thiol. Even at very low concentrations, it has a strong sulfurous, skunk-like odor. Across the samples, higher concentrations tended to accompany higher ratings of the characteristic smell.

Bacio Gelato, which had a strong characteristic odor, contained relatively high levels of VSC3 and other sulfur compounds. The same group of compounds was not detected in Black Jack, which had a mild, woody aroma. In many samples, the other prenylated sulfur compounds followed trends similar to VSC3.

VSC3 is also a major contributor to the undesirable light-struck odor that beer develops through light exposure. A plant’s characteristic smell and a beverage’s deterioration odor are thus connected by the same molecule. Even with the same molecule, the surrounding aroma compounds and what a person is smelling affect the overall impression.

The newly identified family also showed differences. VSC5 had a strong skunk-like aroma, whereas VSC6 and VSC7 were described as milder and reminiscent of garlic and related plants. Their common sulfur chemistry encompasses a range of intensities and qualities.

Testing a trace addition to the ten major compounds

The researchers did not stop at comparing chemical concentrations with odor ratings. They also tested whether adding the substance brought out the characteristic smell. To reconstruct the aroma, they mixed the ten major compounds in Bacio Gelato in proportions based on the analysis.

This mixture somewhat resembled cannabis flowers, but lacked their distinctive pungent, skunk-like character. Adding a trace amount of VSC3 made it smell much more like the flowers.

The sulfurous impression of VSC3 alone became more characteristic of the plant when combined with the other major compounds. The researchers used this reconstitution experiment as evidence that VSC3 is a principal contributor to the characteristic odor. The result shows how a list of the most abundant compounds can miss the substance that makes an aroma distinctive.

Persistence in extracts and changes during growth and storage

The study also examined three concentrated extract samples. All contained VSC3 and VSC5 and were judged to have strong characteristic odors. In two samples, the concentration of VSC5 exceeded that of VSC3, which predominated in the flowers, showing that processing can change their relative proportions.

The researchers then followed four plants over time in a controlled indoor environment. The sulfur compounds associated with the characteristic smell became detectable in the latter part of flowering and increased rapidly toward maturity. Several major compounds reached their highest levels after postharvest treatment, including drying.

After another ten days of storage, however, many of the compounds had declined markedly. VSC5 was an exception, remaining at approximately its preceding level. Odor ratings also weakened, corresponding to the changes in these volatile compounds.

These findings show why aroma comparisons need to consider measurement timing and sample condition as well as variety names. In fact, the initial 13 samples were not matched for storage duration, packaging, or growing conditions. Their concentration differences therefore combine genetic variation with storage and other influences.

What the aroma chemistry does, and does not, establish

A strength of this research is its combination of trace-compound analysis, human sensory assessment, aroma reconstruction, and tracking changes over time. However, the sensory panel consisted of four people, and the study did not measure receptor activity or preferences across a broad population.

The authors also noted structural similarities between this compound family and sulfur compounds in garlic, proposing questions for future biological research. What the study actually measured was chemistry and aroma; health effects were not tested. “Skunk-like” is also an odor description, not a claim that all the compounds match those in skunk secretions.

Summary

In addition to terpenes, trace prenylated sulfur compounds were important to the pungent characteristic odor of cannabis flowers. In particular, adding 3-methyl-2-butene-1-thiol to a mixture of major compounds was key to reproducing a cannabis-like smell.

Related compounds persisted in extracts and changed in abundance from late growth through postharvest processing and storage. The study shows that understanding an aroma requires asking not only what is most abundant, but also what matters in small amounts and when the sample was measured.

The authors included researchers affiliated with companies such as Abstrax Tech. A related patent application was disclosed, and the paper states that no external funding was used.

Reference

Oswald IWH, et al. (2021). Identification of a New Family of Prenylated Volatile Sulfur Compounds in Cannabis Revealed by Comprehensive Two-Dimensional Gas Chromatography. ACS Omega, 6, 31667–31676. Original paper / Open full text