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“Skunky” Cannabis: Environmental Odor Troubleshooting and the “Need-for-Speed”
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  • Jacek A. Koziel*
    Jacek A. Koziel
    Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, Iowa 50011, United States
    *Email: [email protected]. Tel.: +1-515-294-4206.
    More by Jacek A. Koziel
    Orcidhttps://orcid.org/0000-0002-2387-0354
  • Alex Guenther
    Alex Guenther
    Byers Scientific, Bloomington, Indiana 47404, United States
    More by Alex Guenther
  • William Vizuete
    William Vizuete
    Byers Scientific, Bloomington, Indiana 47404, United States
    More by William Vizuete
  • Donald W. Wright*
    Donald W. Wright
    Don Wright & Associates, LLC, Georgetown, Texas 78626, United States
    *Email: [email protected]. Tel.: +1-512-750-1047.
    More by Donald W. Wright
  • Anna Iwasinska
    Anna Iwasinska
    Volatile Analysis Corporation, Grant, Alabama 35747, United States
    More by Anna Iwasinska
Open PDFSupporting Information (1)

ACS Omega

Cite this: ACS Omega 2022, 7, 23, 19043–19047
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https://doi.org/10.1021/acsomega.2c00517
Published May 12, 2022

Copyright © 2022 The Authors. Published by American Chemical Society. This publication is licensed under

CC-BY-NC-ND 4.0 .

Abstract

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Although the “skunky” odor characteristic of cannabis has been widely referenced, its cause has been historically misassigned to unspecified “skunky terpenes”. Recent reports from two independent research groups, the Koziel team (March and April 2021) and Oswald team (August and November 2021), have corrected this misassignment by linking the “skunky” character of industrial hemp and cannabis to 3-methyl-2-butene-1-thiol (321MBT). A recent USPTO patent application review clearly indicated that the Oswald team should take full credit for the discovery of this link with respect to cannabis. However, the August 19, 2021 publication of their patent application appears to be their formal public disclosure of 321MBT as the primary source odorant which is responsible for the targeted “skunky” odor. This date is well after the March and April 2021 public disclosures by the Koziel team for the 321MBT/“skunky” odor link relative to both cannabis and industrial hemp. This Viewpoint summarizes the investigative strategy leading to the public disclosure of this historically elusive link. It is presented from the perspective of the rapid multidimensional–gas chromatography–mass spectrometry–olfactometry (i.e., MDGC-MS-O) based odorant-prioritization “screening” approach, as applied by the Koziel team.

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Environmental Odor Troubleshooting

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The following comments are submitted in response to Oswald et al. (1) The Oswald et al. (1) integration of hyphenated techniques (i.e., GC × GC-TOF-MS/FID/SCD) represents an almost perfect tool for pushing the limits relative to compositional analysis. However, from the standpoint of a practical environmental odor mitigation strategy focus, multidimensional–gas chromatography–mass spectrometry–olfactometry (MDGC-MS-O)-based odorant prioritization “screening” to the smallest essential subset of compounds can be more instructive. Simply stated, with respect to environmental odor problem solving, “less can often be more”. A simplified, priority-odorant subset can, more directly, satisfy the “need-for-speed” relative to environmental odor problem solving.
While Oswald et al. (1) appear to have an excellent and thorough treatment of the subject of “skunky” cannabis, we would like to alert readers to the Koziel et al. (2,3) public disclosure of the relationship between 321MBT and the “skunky” characteristic of both hemp and cannabis. While the November 12, 2021 publication of Oswald et al. (1) does cite the Rice and Koziel (2015) (4) paper, it fails to cite the coauthor’s subsequent collaborative work (Byers Scientific, Don Wright & Associates, Iowa State University, and Volatile Analysis Corporation) and public disclosures of the connection between “skunky” cannabis and 321MBT. (2,3) Public disclosure was by way of a March 22, 2021 Press Release (2) and an April 19, 2021 Koziel et al. (3) plenary lecture at the seventh NOSE International Conference on Environmental Odor Monitoring and Control. Two follow-up media articles were published on April 21 and June 22, 2021, respectively. (5,6)Table S1 (Supporting Information) provides a summary of our understanding of the chronological discovery (1) and public disclosure (2,3) timeline for the link between 321MBT and “skunky” cannabis/hemp odor. While these authors were disappointed that their public disclosure was not cited in the excellent Oswald et al. (1) article, it was reassuring that these two independent and very different approaches to the “skunky” cannabis question yielded the same major conclusion.
We would like to offer the following Viewpoint to contrast these two disparate odor investigative strategies that arrive at the same major conclusion relative to the “skunky” cannabis odor, i.e., (a) vs (b):
(a)

The rapid screening approach; odorant prioritization by MDGC-MS-olfactometry; direct chemical/compositional and sensory analysis by Koziel et al. (7)

(b)

The comprehensive but more labor-intensive approach by GC × GC-TOF-MS/FID/SCD; indirect chemical/compositional followed by sensory analysis by Oswald et al. (1)

While this Viewpoint focuses on the skunky cannabis case, we believe it is applicable to a wide range of environmental odor-related questions and challenges.

MDGC-MS-Olfactometry-Based Odorant Prioritization and the “Need-for-Speed”

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The MDGC-MS-O-based approach to rapid screening for character-defining odorants (8) has emerged for these authors by way of many years of odor troubleshooting in the industry. (9−12) A company faced with a crisis-driven odor/flavor quality defect in a commercial product, process, or environment must quickly respond to this quality excursion in order to protect the market share and customer base. Responding to such real-world crisis issues has taught us that mitigation strategies can often be focused on and resolved without resorting to comprehensive and time-consuming compositional analysis.
It is often the case that odor quality challenges can be quickly traced to character-defining odorants, (7,9−12) single odorous VOCs that match the odor character of the quality “defect” and are deemed, therefore, primarily responsible for imparting that defect. Other cases may reflect somewhat greater complexity than the single “bad-actor” model, with a targeted odor defect traceable to a very small subset of compounds from the source’s total VOC emission profile. In either case, it is typical that such odor quality troubleshooting can be quickly focused onto the smallest impact-priority subset by integrating a direct sensory monitoring component (i.e., olfactometry) into the conventional GC-MS analytical system (Figure 1).

Figure 1

Figure 1. Overview of MDGC-MS-O systems integration: AromaTrax system from Volatile Analysis Corporation on an Agilent platform. Major components labeled as follows: (1) 6890 GC; (2) 5975B MSD; (3) manual SPME field sampler; (4) heart-cut valve; (5) cryo-trap valve; (6) Aromatrax data processing interface; (7) heated transfer line; (8) olfactory detector; and (9) human “sensor”.

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This critical sensory integration permits direct “screening” of the source’s total VOC emission profile in a single GC-O run. Figure 1 illustrates the major integrated components of an MDGC-MS-O system, such as that used for the Koziel et al. (2,3) odorant prioritization assessment of the industrial hemp environment. The AromaTrax system pictured is closely representative of the system which was used by the lead investigator in that investigation. Most importantly, this figure includes the integrated component, which these authors believe reflects the most significant difference between the Koziel et al. (3) and Oswald et al. (1) approaches: the “human sensor” operating in parallel with mass spectrometric detection. Our past publications cover MDGC-MS-O instrumentation, components, systems integration, and investigative strategies in great detail. (7,13−17)

MDGC-MS-O-Based Odorant Prioritization Applied to Cannabis/Industrial Hemp

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The reported “skunky” odor character, historically described for cannabis and industrial hemp grow operations, proved to be an excellent candidate for MDGC-MS-O-based odorant prioritization screening. (3) The “skunky” character had, historically, been attributed to undefined “skunky terpenes”.
These authors’ initial screening efforts were first directed at an industrial hemp growing operation in Central Texas. Industrial hemp was selected as a surrogate for cannabis, primarily for reasons of logistical convenience and accessibility to the Texas-based odor experts. The Texas legislature had only recently legalized the growing of industrial hemp, and the Pur Isolabs operation (Bergheim, TX) was, reportedly, one of the first permitted grantees in the state. The following Tables 1–3 reflect the first-approximation impact-priority odorant ranking profile which was derived from the initial SPME fiber-based indoor air sample collections from within the operation’s hemp drying trailer. The six air sample collections approximated a 3X serial dilution. Serial dilution was approximated by exposing the SPME fibers simultaneously to the environment for 1.8, 5.0, and 15 min, respectively.
Table 1. First-Tier (Group 1), Odor Impact-Priority Compoundsa
 GC column retention time (min)tentative chemical IDodor descriptor
group 112.0beta-myrcene“characteristic”, “geranium leaf”
10.4alpha-pinene“characteristic”, “pine”
13.9unknown (likely a C4-substituted pyrazine)“musty”, “nutty”, “foul”
16.7unknown (likely trans-2-nonenal)“musty”, “cardboard”, “vegetable”
13.1d,l-limonene“citrus”
a

Dominant impact-priority subset at the time of on-site assessment and odor collection.

Table 2. Second-Tier (Group 2) Odor Modifier Compounds, Including 321MBT, “Masked” by the Group 1 Odorants
 GC column retention time (min)tentative chemical IDodor descriptor
group 211.8beta-pinene“characteristic”, “pine”
7.63-methyl-2-butene-1-thiol“skunky”, “foul”
7.2hexanal“grassy”, “green”
12.7unknown (possibly 1-octene-3-one)“earthy”, “mushroom”
3.5diacetyl“buttery”
8.72-hexenal“grassy”, “herbaceous”
Table 3. Additional Possible Minor Impact VOCs in Group 3 That Are “Masked” by the Group 1 and 2 Odorants
 GC column retention time (min)tentative chemical IDdescriptor
group 32.8methyl mercaptan“fecal”
18.8para-cresol“barnyard”
8.3unknown (possibly methyl butanoate)“fruity”
10.9camphene“camphor”
13.21,8-cineole“eucalyptus”
∼14.7+para-xylene and other alkyl benzenesundefined
∼10.0 to 28.0a plethora of other terpenes beyond the abovevarious
With respect to the “need-for-speed”, it is believed to be noteworthy that the overall odorant ranking profile (Tables 1–3) emerged for the single MDGC-MS-O investigator/panelist after only 4 person-days (i.e., including travel to/from the site and in-laboratory MDGC-MS-O analysis, on-site odor assessment, and SPME air sample collection). It is also noteworthy that the initial link between the dominant “skunky” odorant carrier and the 7.6 min GC column retention time was made during the fourth MDGC-MS-O run of the in-laboratory phase or approximately 4 person-hours from the start (Figure 2). In addition, as a result of prior knowledge of the expected retention time of the familiar “skunky” odor carrier compound (i.e., 321MBT), (13,14,18) it was possible to make the tentative peak assignment hypothesis within that time as well (i.e., 4 person-hours from the start).

Figure 2

Figure 2. GC-O odor profile (captured using the AromaTrax software from Volatile Analysis Corporation) enabled rapid linking of the “skunky” smell to 321MBT. Aromagram presents a GC-O odor profile overview of air samples collected, using a SPME fiber exposed for 15 min to the indoor environment of the hemp-drying room.

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It should be noted that, in this case, the dominant “skunky” note @7.6 min (Figure 2) was relegated to the status of a second-tier odor modifier. This was, in fact, consistent with the associated on-site composite odor assessment which was carried out at this facility. Specifically, there was no perceived “skunky” odor character that was recognizable, by the investigator/panelist, at the time of the on-site assessment and SPME air sample collection. This indicated that the 321MBT concentration was below the recognition threshold and was therefore masked by the Group 1 impact-priority subset of odorants (Table 1). The “rolling unmasking effect” (RUE), (7) as illustrated in Figure 3, reflects the odor impact-priority ranking of Tables 1–3. Under other varietal, seasonal, growing, or processing conditions, this ranking could reasonably be expected to change. By way of example, the downwind odor of large Texas bluebonnet fields (the state flower of Texas) is dominated by a single compound, 1,4-dimethoxybenzene, a “sweet”/“heavy”/“floral” aroma. (7) However, this odor is only detectable at the peak of the flower’s growth cycle (i.e., just before seasonal die-off). Up until that time, the dense blue fields, while beautiful to look at, will not present with significant downwind odor impact. Likewise, dense prairie verbena colonies, like those of the Texas bluebonnet, are also dominated, at their seasonal environmental odor-impacting peak, by the nonterpene, semivolatile aromatic compound, p-cresol. (7) As a result, in the case of the prairie verbena colonies, the downwind odor is dominated by a “barnyard”/“hog-truck” odor driven by p-cresol, the dominant odor rising above the masking capability of the dense, odorous terpene emissions at the source. (7) This relationship and its investigation are explored in detail in the Supporting Information of a recent publication. (7) Ironically, the 321MBT/“skunky” hemp link appears to reflect the same type of relationship as described for the Texas bluebonnet and prairie verbena. Specifically, a potent, nonterpene odorant (321MBT) can rise to odor impact-priority dominance (under seasonal or varietal conditions), emerging from the dense, odorous terpene background emissions near the source. The 321MBT/“skunky” hemp link hypothesis was subsequently validated and confirmed to exist for cannabis, as well, by the collaborative Byers Scientific research team, utilizing an odor-matching validation process as referenced below. (2,3)

Figure 3

Figure 3. “Rolling unmasking effect” (RUE), i.e., group 1 “masking” groups 2 and 3 and group 2 “masking” group 3 (in the absence of group 1 odorants). Diagram illustrates, to a first approximation, the relationship between the odor impact-priority ranking profile from the industrial hemp drying room relative to the expected downwind odor impact. The RUE concept of environmental odor dispersion is examined in detail by Koziel et al. (7)

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Odor-Matching Hypothesis Validation versus Reverse Engineering Hypothesis Development

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The Koziel et al. (3) “direct” approach and the “indirect” approach of Oswald et al. (1) appear to be in agreement relative to the power of synthetic, odor-match formulations for focusing communication between “human sensors” regarding odor. In the case of Koziel et al., (3) synthetic odor matching is used to validate an impact-priority subset hypothesis arising directly from MDGC-MS-O-based odorant prioritization. In contrast, in the case of Oswald et al., (1) odor matching (i.e., which appears to be referred to by the authors as “reverse engineering”) is used to indirectly/sequentially develop and validate an impact-priority odorant hypothesis.
Communication between human “sensors” regarding an environmental odor of interest can be much more challenging when compared, for example, to the sense of color perception. (7) With respect to color perception, color wheels can be very effective tools for developing consensus with respect to an “undefined” color of interest, whether the queried sensory “panelist” is a sensory professional or a layperson. Sensory professionals representing various industries have developed “descriptive-analysis”-based odor/aroma/flavor wheels which attempt to emulate the color-wheel as applied to color perception. (19,20) The practical challenge for such odor wheels is that they rely on relatively subjective descriptors such as “grassy”, “herbaceous”, “skunky”, “fecal”, etc.
The odorant prioritization-based simplification of odor profiles to a single, character-defining odorant (or to the smallest subset of odorants) opens up the possibility of introducing a reconciling tool for odor that is more closely aligned with the simplicity of the color wheel for color. This tool was used in chemical odor matching. (7,15) In its simplest form, the odor-match query asked of a lay panelist relative to a targeted environmental odor is a simple “YES/NO” when presented with a trace amount of a high-purity reference chemical. Utilizing this process, one can screen for a chemical’s odor-match fidelity to a “suspect”, character-defining odorant. As we argued earlier, (7) this simplicity negates the requirement, on the part of the panelist, for extensive training, experience, or memory acuity relative to odor recognition. The only requirement is the usual application of his/her sense of smell (i.e., assumed or demonstrated to be properly functioning).
Odor-matching hypothesis validation can reflect a range of survey formalities and complexity. These surveys can range from (1) informal on-instrument demonstration/introductions of designated client representatives to a product’s “suspect” odor-defect source, to (2) informal on-instrument demonstration/introductions of a layperson sensory panel (e.g., volunteer representatives from impacted downwind citizenry) to a hypothesized link between an environmental odor issue and a “suspect” chemical odorant, to (3) formal odor-match fidelity grading by a professional sensory panel of a multicomponent synthetic odor-match formulation, to (4) formal odor-match fidelity grading of a multicomponent synthetic odor-match formulation by a seated jury in a civil trial.

Conclusion

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Clearly, the work of Oswald et al. (1) has generated excellent VOC compositional information regarding cannabis emissions (including a family of compounds related to 321MBT). The Oswald et al. (1) integration of hyphenated techniques (i.e., GC × GC-TOF-MS/FID/SCD) represents an almost perfect tool for pushing the limits relative to odor compositional analysis. Clearly, there may be questions beyond odor impact, for which exhaustive emission compositional data may be more important (e.g., toxicology and atmospheric chemistry). However, from the standpoint of a practical environmental odor mitigation strategy focus, MDGC-MS-O-based odorant prioritization “screening” to the smallest essential subset of compounds can be more instructive. (7,9−12) Simply stated, with respect to environmental odor problem solving and troubleshooting, “less can often be more”. A simplified, priority-odorant field can more directly satisfy the “need-for-speed” relative to environmental odor problem solving.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.2c00517.

  • Table S1. Chronological summary of uncovering the link between 321MBT and “skunky” cannabis/hemp odor (PDF)

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Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

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  • Corresponding Authors
  • Authors
    • Alex Guenther - Byers Scientific, Bloomington, Indiana 47404, United States
    • William Vizuete - Byers Scientific, Bloomington, Indiana 47404, United States
    • Anna Iwasinska - Volatile Analysis Corporation, Grant, Alabama 35747, United States
  • Notes
    The authors declare the following competing financial interest(s): Three commercial entities are represented among the collaborative team (Byers Scientific, Don Wright & Associates, LLC, and Volatile Analysis Corporation).

Acknowledgments

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We would like to express appreciation to the Volatile Analysis Corporation for (1) allowing the panelist (D.W.W.) access to their AromaTrax software and instrumentation in this effort and (2) providing review and feedback on the manuscript. We would also like to express appreciation to Austin Rupple and Pur Isolabs in Bergheim, Texas, for allowing the research team access to their industrial hemp grow and processing facility.

References

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    Nielsen, Lawrence T.; Eaton, David K.; Wright, Donald W.; Schmidt-French, Barbara
    Journal of Cave and Karst Studies (2006), 68 (1), 27-31CODEN: JCKSFK; ISSN:1090-6924. (National Speleological Society)
    The odors in a central Texas cave with a large roosting population of Mexican free-tailed bats (Tadarida brasiliensis mexicana) were identified and related to captive individual bats. Solid phase microextn. (SPME) was used to sample and conc. the volatile orgs. from the cave and individual bats. Odors were detected organoleptically and simultaneously quantified and identified. The characteristic odor for T. b. mexicana is due principally to 2'-aminoacetophenone.
  12. 12
    Koziel, J. A.; Cai, L.; Wright, D.; Hoff, S. Solid phase microextraction as a novel air sampling technology for improved, GC-Olfactometry-based, assessment of livestock odors. J. Chromatogr. Sci. 2006, 44, 451– 457,  DOI: 10.1093/chromsci/44.7.451
    Google Scholar
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    Solid-Phase Microextraction as a Novel Air Sampling Technology for Improved, GC-Olfactometry-Based Assessment of Livestock Odors
    Koziel, Jacek A.; Cai, Lingshuang; Wright, Donald W.; Hoff, Steven J.
    Journal of Chromatographic Science (2006), 44 (7), 451-457CODEN: JCHSBZ; ISSN:0021-9665. (Preston Publications)
    Air sampling and characterization of odorous livestock gases is one of the most challenging anal. tasks. This is because of low concns., physicochem. properties, and problems with sample recoveries for typical odorants. Livestock operations emit a very complex mixt. of volatile org. compds. (VOCs) and other gases. Many of these gases are odorous. Relatively little is known about the link between characteristic VOCs/gases and, specifically, about the impact of characteristic odorants downwind from sources. In this research, solid-phase microextn. (SPME) is used for field air sampling of odors downwind from swine and beef cattle operations. Sampling time ranges from 20 min to 1 h. Samples are analyzed using a com. gas chromatog.-mass spectrometry-olfactometry system. Odor profiling efforts are directed at odorant prioritization, with respect to distance from the source. The results indicate the odor downwind is increasingly defined by a smaller no. of high-priority odorants. These "character defining" odorants appear to be dominated by compds. of relatively low volatility, high mol. wt., and high polarity. In particular, p-cresol alone appears to carry much of the overall odor impact for swine and beef cattle operations. Of particular interest is the character-defining odor impact of p-cresol as far as 16 km downwind of the nearest beef cattle feedlot. The findings are highly relevant to scientists and engineers working on improved air sampling and anal. protocols and on improved technologies for odor abatement. More research evaluating the use of p-cresol and a few other key odorants as a surrogate for overall odor dispersion modeling is warranted. (c) 2006 Preston Publications.
  13. 13
    Eaton, D. K.; Nielsen, L. T.; Wright, D. W. An integrated MDGC-MS-Olfactometry Approach to Aroma and Flavor Analysis. In Sensory Directed Flavor Analysis; Marsili, R., Ed.; Taylor and Francis Group LLC: New York, 2007; pp 81– 110.
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    There is no corresponding record for this reference.
  14. 14
    Wright, D. W.; Nielsen, L.; Eaton, D.; Kuhrt, F.; Koziel, J. A.; Cai, L.; Parker, D. B. Animal Odor Assessment - Chickens, Pigs, Bats or Cats; it is Still Analytical Chemistry. In Proceedings of the National Poultry Waste Management Symposium; Springdale AK, USA, 23–25 Oct 2006.
    Google Scholar
    There is no corresponding record for this reference.
  15. 15
    Wright, D. W.; Eaton, D. K.; Nielsen, L. T.; Kuhrt, F. W.; Koziel, J. A.; Cai, L.; Lo, Y.; Parker, D. B.; Buser, Z. Synthetic CAFO odor formulation; an effective technique for validation of odorant prioritizations. In Proceedings of the Ecological Society of America Conference; Washington, DC, USA, 5–8 June 2006.
    Google Scholar
    There is no corresponding record for this reference.
  16. 16
    Wright, D. Application of multidimensional gas chromatography techniques to aroma analysis. In Techniques for Analyzing Food Aroma; Ray, M., Ed.; Marcel Dekker, Inc.: NY, 1997; Chapter 5.
    Google Scholar
    There is no corresponding record for this reference.
  17. 17
    Bulliner, E.A. IV.; Koziel, J. A.; Cai, L.; Wright, D. Characterization of livestock odors using steel plates, solid phase microextraction, and multidimensional - gas chromatography-mass spectrometry- olfactometry. J. Air Waste Manage. Assoc. 2006, 56, 1391– 1403,  DOI: 10.1080/10473289.2006.10464547
    Google Scholar
    17
    Characterization of livestock odors using steel plates, solid-phase microextraction, and multidimensional gas chromatography-mass spectrometry-olfactometry
    Bulliner, Edward A., IV; Koziel, Jacek A.; Cai, Lingshuang; Wright, Donald
    Journal of the Air & Waste Management Association (2006), 56 (10), 1391-1403CODEN: JAWAFC; ISSN:1096-2247. (Air & Waste Management Association)
    Livestock operations are assocd. with emissions of odor, gases, and particulate matter (PM). Livestock odor characterization is one of the most challenging anal. tasks. This is because odor-causing gases are often present at very low concns. in a complex matrix of less important or irrelevant gases. The objective of this project was to develop a set of characteristic ref. odors from a swine barn in Iowa and, in the process, identify compds. causing characteristic swine odor. Odor samples were collected using a novel sampling methodol. consisting of clean steel plates exposed inside and around the swine barn for ≤1 wk. Steel plates were then transported to the lab. and stored in clean jars. Head-space solid-phase microextn. was used to ext. characteristic odorants collected on the plates. All of the analyses were conducted on a gas chromatog.-mass spectrometry-olfactometry system where the human nose is used as a detector simultaneously with chem. anal. via mass spectrometry. Multidimensional chromatog. was used to isolate and identify chems. with high-characteristic swine odor. The effects of sampling time, distance from a source, and the presence of PM on the abundance of specific gases, odor intensity, and odor character were tested. Steel plates were effectively able to collect key volatile compds. and odorants. The abundance of specific gases and odor was amplified when plates collected PM. The results of this research indicate that PM is major carrier of odor and several key swine odorants. Three odor panelists were consistent in identifying p-cresol as closely resembling characteristic swine odor, as well as attributing to p-cresol the largest odor response out of the samples. Further research is warranted to det. how the control of PM emissions from swine housing could affect odor emissions.
  18. 18
    Lusk, L. T.; Murakami, A.; Nielsen, L.; Kay, S.; Ryder, D. Beer photooxidation creates two compounds with aromas indistinguishable from 3-methyl-2-butene-1-thiol. J. of the Am. Soc. of Brew. Chemists. 2009, 67, 189– 192,  DOI: 10.1094/ASBCJ-2009-0910-02
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    Lusk, Lance T.; Murakami, Aki; Nielsen, Lawrence; Kay, Susan; Ryder, David
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    Beer photooxidn. (lightstruck reaction) creates the well-known, intensely flavor-active compd. 3-methyl-2-butene-1-thiol (MBT). The sensory threshold in beer for this malodorous compd. is 2-7 ng/L. Using solid-phase microextn. and multidimensional GC-olfactometry, we discovered two previously unidentified compds. with aromas indistinguishable from the "skunky" or "foxy" aroma used to describe MBT. These addnl. skunky aroma compds. undoubtedly contribute to the overall lightstruck character in beer. Addnl., we discovered that MBT and one of the two other compds. slowly formed during beer thermal oxidn. in the absence of light.
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  1. Donald W. Wright, Jacek A. Koziel, Fred W. Kuhrt, Anna Iwasinska, David K. Eaton, Landon Wahe. Odor-Cued Grab Air Sampling for Improved Investigative Odorant Prioritization Assessment of Transient Downwind Environmental Odor Events. ACS Omega 2024, 9 (27) , 29290-29299. https://doi.org/10.1021/acsomega.4c00531
  2. Parandaman Arathala, Rabi A. Musah. Theoretical Insights into the Gas-Phase Oxidation of 3-Methyl-2-butene-1-thiol by the OH Radical: Thermochemical and Kinetic Analysis. The Journal of Physical Chemistry A 2024, 128 (11) , 2136-2149. https://doi.org/10.1021/acs.jpca.3c07775
  3. Iain W. H. Oswald, Twinkle R. Paryani, Manuel E. Sosa, Marcos A. Ojeda, Mark R. Altenbernd, Jonathan J. Grandy, Nathan S. Shafer, Kim Ngo, Jack R. Peat, III, Bradley G. Melshenker, Ian Skelly, Kevin A. Koby, Michael F. Z. Page, Thomas J. Martin. Minor, Nonterpenoid Volatile Compounds Drive the Aroma Differences of Exotic Cannabis. ACS Omega 2023, 8 (42) , 39203-39216. https://doi.org/10.1021/acsomega.3c04496
  4. Davi de Ferreyro Monticelli, Cynthia Pham, Sahil Bhandari, Amanda Giang, Nadine Borduas-Dedekind, Naomi Zimmerman. Following the smell: terpene emission profiles through the cannabis life-cycle. Environmental Science: Processes & Impacts 2025, 51 https://doi.org/10.1039/D5EM00253B
  5. Lorenzo Cucinotta, Gemma De Grazia, Antonella Satira, Luigi Mondello, Danilo Sciarrone. Boosting the odour perception of trace compounds exploiting three-dimensional GC-O with MS/FID simultaneous detection. Journal of Essential Oil Research 2024, 36 (6) , 578-587. https://doi.org/10.1080/10412905.2024.2380399
  6. Nate Seltenrich. Odor Control in the Cannabis Industry: Lessons from the New Kid on the Block. Environmental Health Perspectives 2022, 130 (6) https://doi.org/10.1289/EHP11449
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  • Abstract

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    Figure 1

    Figure 1. Overview of MDGC-MS-O systems integration: AromaTrax system from Volatile Analysis Corporation on an Agilent platform. Major components labeled as follows: (1) 6890 GC; (2) 5975B MSD; (3) manual SPME field sampler; (4) heart-cut valve; (5) cryo-trap valve; (6) Aromatrax data processing interface; (7) heated transfer line; (8) olfactory detector; and (9) human “sensor”.

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    Figure 2

    Figure 2. GC-O odor profile (captured using the AromaTrax software from Volatile Analysis Corporation) enabled rapid linking of the “skunky” smell to 321MBT. Aromagram presents a GC-O odor profile overview of air samples collected, using a SPME fiber exposed for 15 min to the indoor environment of the hemp-drying room.

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    Figure 3

    Figure 3. “Rolling unmasking effect” (RUE), i.e., group 1 “masking” groups 2 and 3 and group 2 “masking” group 3 (in the absence of group 1 odorants). Diagram illustrates, to a first approximation, the relationship between the odor impact-priority ranking profile from the industrial hemp drying room relative to the expected downwind odor impact. The RUE concept of environmental odor dispersion is examined in detail by Koziel et al. (7)

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  • References

    This article references 20 other publications.

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      Oswald, I. W. H.; Ojeda, M. A.; Pobanz, R. J.; Koby, K. A.; Buchanan, A. J.; Del Rosso, J.; Guzman, M. A.; Martin, T. J. Identification of a New Family of Prenylated Volatile Sulfur Compounds in Cannabis Revealed by Comprehensive Two-Dimensional Gas Chromatography. ACS Omega 2021, 6 (47), 31667– 31676,  DOI: 10.1021/acsomega.1c04196
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      Identification of a New Family of Prenylated Volatile Sulfur Compounds in Cannabis Revealed by Comprehensive Two-Dimensional Gas Chromatography
      Oswald, Iain W. H.; Ojeda, Marcos A.; Pobanz, Ryan J.; Koby, Kevin A.; Buchanan, Anthony J.; Del Rosso, Josh; Guzman, Mario A.; Martin, Thomas J.
      ACS Omega (2021), 6 (47), 31667-31676CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
      Cannabis sativa L. produces over 200 known secondary metabolites that contribute to its distinctive aroma. Studies on compds. traditionally assocd. with the scent of this plant have focused on those within the terpenoid class. These isoprene-derived compds. are ubiquitous in nature and are the major source of many plant odors. Nonetheless, there is little evidence that they provide the characteristic "skunk-like" aroma of cannabis. To uncover the chem. origins of this scent, we measured the arom. properties of cannabis flowers and concd. exts. using comprehensive two-dimensional gas chromatog. equipped with time-of-flight mass spectrometry, flame ionization detection, and sulfur chemiluminescence. We discovered a new family of volatile sulfur compds. (VSCs) contg. the prenyl (3-methylbut-2-en-1-yl) functional group that is responsible for this scent. In particular, the compd. 3-methyl-2-butene-1-thiol was identified as the primary odorant. We then conducted an indoor greenhouse expt. to monitor the evolution of these compds. during the plant's lifecycle and throughout the curing process. We found that the concns. of these compds. increase substantially during the last weeks of the flowering stage, reach a max. during curing, and then drop after just one week of storage. These results shed light on the chem. origins of the characteristic aroma of cannabis and how volatile sulfur compd. prodn. evolves during plant growth. Furthermore, the chem. similarity between this new family of VSCs and those found in garlic (allium sativum) suggests an opportunity to also investigate their potential health benefits.
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      Long, E. Byers Scientific, Iowa State University, and Odor Experts Identify the Volatile Chemical Compound Responsible for Cannabis Odor Complaints; Business Wire (a Berkshire Hathaway Company): Bloomington, IN, USA, 22 March 2021. Available online: https://www.businesswire.com/news/home/20210322005837/en/Byers-Scientific-Iowa-State-University-and-Odor-Experts-Identify-the-Volatile-Chemical-Compound-Responsible-for-Cannabis-Odor-Complaints (accessed on 17 January 2022).
      There is no corresponding record for this reference.
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      Koziel, J. A.; Guenther, A.; Byers, M.; Iwasinska, A.; Parker, D.; Wright, D. Update on the Development of a New ASTM Standard for Environmental Odor Assessment. Plenary Lecture at the NOSE2020. In Proceedings of the 7th International Conference on Environmental Odour Monitoring and Control, Virtual Conference , Online, 18–21 April 2021.
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      Rice, S.; Koziel, J. A. Characterizing the smell of marijuana by odor impact of volatile compounds: An application of simultaneous chemical and sensory analysis. PLoS One 2015, 10, e0144160  DOI: 10.1371/journal.pone.0144160
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      Characterizing the smell of marijuana by odor impact of volatile compounds: an application of simultaneous chemical and sensory analysis
      Rice, Somchai; Koziel, Jacek A.
      PLoS One (2015), 10 (12), e0144160/1-e0144160/17CODEN: POLNCL; ISSN:1932-6203. (Public Library of Science)
      Recent US legislation permitting recreational use of marijuana in certain states brings the use of marijuana odor as probable cause for search and seizure to the forefront of forensic science, once again. This study showed the use of solid-phase microextn. with multidimensional gas chromatog.-mass spectrometry and simultaneous human olfaction to characterize the total aroma of marijuana. The application of odor activity anal. offers an explanation as to why high volatile chem. concn. does not equate to most potent odor impact of a certain compd. This suggests that more attention should be focused on highly odorous compds. typically present in low concns., such as nonanal, decanol, o-cymene, benzaldehyde, which have more potent odor impact than previously reported marijuana headspace volatiles.
    5. 5
      Gehr, D. Why does cannabis smell like skunk? This Iowa State professor has answers; Ames Tribune. Published on April 21, 2021. Available online: https://www.amestrib.com/story/news/2021/04/19/weed-iowa-state-university-isu-participates-research-cause-skunky-skunk-why-marijuana-smell-pot/7010613002/ (accessed on March 02, 2022).
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      Leigh, C. Researchers May Have Discovered the Cause of the Skunky Smell from Cannabis; Veriheal. Published on June 22, 2021. Available online: https://www.veriheal.com/blog/researchers-may-have-discovered-the-cause-of-the-skunky-smell-from-cannabis/ (accessed on March 02, 2022).
      There is no corresponding record for this reference.
    7. 7
      Wright, D. W.; Koziel, J. A.; Parker, D. B.; Iwasinska, A.; Hartman, T. G.; Kolvig, P.; Wahe, L. Qualitative Exploration of the ‘Rolling Unmasking Effect’ for Downwind Odor Dispersion from a Model Animal Source. Int. J. Environ. Res. Public Health 2021, 18, 13085,  DOI: 10.3390/ijerph182413085
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    8. 8
      McGorrin, R. J. Character-impact flavor compounds. In Sensory Directed Flavor Analysis; Marsili, R., Ed.; Taylor & Francis Group: Boca Raton, FL, 2007; Chapter 9.
      There is no corresponding record for this reference.
    9. 9
      Wright, D. W.; Mahler, K. O.; Ballard, L. B. The Application of an Expanded Multidimensional G.C. System to Complex Fragrance Evaluations. J. Chromatogr. Sci. 1986, 24, 60– 65,  DOI: 10.1093/chromsci/24.2.60
      9
      The application of an expanded multidimensional GC system to complex fragrance evaluations
      Wright, D. W.; Mahler, K. O.; Ballard, L. B.
      Journal of Chromatographic Science (1986), 24 (2), 60-5CODEN: JCHSBZ; ISSN:0021-9665.
      A comprehensive multidimensional gas chromatog. (GC) system is described which can greatly simplify the tasks of sepn. and odor evaluation for complex fragrance blends. Two dual-column switching systems based on the Deans (1968) pressure balance technique are shown operating in tandem, making possible a unique double heart-cutting capability. This arrangement permits optimum sepns. to be realized through the normal 2-column heart-cut operations prior to a 2nd heart-cut, sending isolated peaks or fractions from the effluent of column 2 to a sniffing port for fragrance evaluation. The applications of other ancillary devices such as a sniffing port, fraction collector, and cold trap are also described.
    10. 10
      Wright, D. W.; Nielsen, L.; Eaton, D.; Kuhrt, F.; Koziel, J. A.; Spinhirne, J. P.; Parker, D. B. Multidimensional GC-MS-olfactometry for identification and prioritization of malodors from confined animal feeding operations. J. Agric. Food Chem. 2005, 53, 8663– 8672,  DOI: 10.1021/jf050763b
      10
      Multidimensional Gas Chromatography-Olfactometry for the Identification and Prioritization of Malodors from Confined Animal Feeding Operations
      Wright, Donald W.; Eaton, David K.; Nielsen, Lawrence T.; Kuhrt, Fred W.; Koziel, Jacek A.; Spinhirne, Jarett P.; Parker, David B.
      Journal of Agricultural and Food Chemistry (2005), 53 (22), 8663-8672CODEN: JAFCAU; ISSN:0021-8561. (American Chemical Society)
      Odor profiling efforts were directed at applying to high-d. livestock operations some of the lessons learned in resolving past, highly diverse, odor-focused investigations in the consumer product industry. Solid-phase microextn. (SPME) was used for field air sampling of odorous air near and downwind of a beef cattle feed yard and a swine finisher barn in Texas. Multidimensional gas chromatog.-olfactometry (MD-GC-O) was utilized in an attempt to define and prioritize the basic building blocks of odor character assocd. with these livestock operations. Although scores of potential odorant volatiles have been previously identified in high-d. livestock operations, the odor profile results developed herein suggest that only a very few of these may constitute the preponderance of the odor complaints assocd. with these environments. This appeared to be esp. true for the case of increasing distance from both cattle feed yard and swine barn facilities, with p-cresol consistently taking on the dominant odor impact role with ever increasing distance. In contrast, at- or near-site odor profiles were shown to be much more complex, with many of the well-known lower tier odorant compds. rising in relative significance. For the cattle feed yard at- or near-site odor profiles, trimethylamine was shown to represent a significantly greater individual odor impact relative to the more often cited livestock odorants such as hydrogen sulfide, the org. sulfides, and volatile fatty acids. This study demonstrates that SPME combined with a MD-GC-O-mass spectrometry system can be used for the sampling, identification, and prioritization of odors assocd. with livestock.
    11. 11
      Nielsen, L. T.; Eaton, D. K.; Wright, D. W.; Schmidt-French, B. Characteristic odors of Tadarida braziliensis Mexicana chiroptera: Molossidae. J. Cave Karst Stud. 2006, 68, 27– 31
      11
      Characteristic odors of Tadarida brasiliensis Mexicana Chiroptera: Molossidae
      Nielsen, Lawrence T.; Eaton, David K.; Wright, Donald W.; Schmidt-French, Barbara
      Journal of Cave and Karst Studies (2006), 68 (1), 27-31CODEN: JCKSFK; ISSN:1090-6924. (National Speleological Society)
      The odors in a central Texas cave with a large roosting population of Mexican free-tailed bats (Tadarida brasiliensis mexicana) were identified and related to captive individual bats. Solid phase microextn. (SPME) was used to sample and conc. the volatile orgs. from the cave and individual bats. Odors were detected organoleptically and simultaneously quantified and identified. The characteristic odor for T. b. mexicana is due principally to 2'-aminoacetophenone.
    12. 12
      Koziel, J. A.; Cai, L.; Wright, D.; Hoff, S. Solid phase microextraction as a novel air sampling technology for improved, GC-Olfactometry-based, assessment of livestock odors. J. Chromatogr. Sci. 2006, 44, 451– 457,  DOI: 10.1093/chromsci/44.7.451
      12
      Solid-Phase Microextraction as a Novel Air Sampling Technology for Improved, GC-Olfactometry-Based Assessment of Livestock Odors
      Koziel, Jacek A.; Cai, Lingshuang; Wright, Donald W.; Hoff, Steven J.
      Journal of Chromatographic Science (2006), 44 (7), 451-457CODEN: JCHSBZ; ISSN:0021-9665. (Preston Publications)
      Air sampling and characterization of odorous livestock gases is one of the most challenging anal. tasks. This is because of low concns., physicochem. properties, and problems with sample recoveries for typical odorants. Livestock operations emit a very complex mixt. of volatile org. compds. (VOCs) and other gases. Many of these gases are odorous. Relatively little is known about the link between characteristic VOCs/gases and, specifically, about the impact of characteristic odorants downwind from sources. In this research, solid-phase microextn. (SPME) is used for field air sampling of odors downwind from swine and beef cattle operations. Sampling time ranges from 20 min to 1 h. Samples are analyzed using a com. gas chromatog.-mass spectrometry-olfactometry system. Odor profiling efforts are directed at odorant prioritization, with respect to distance from the source. The results indicate the odor downwind is increasingly defined by a smaller no. of high-priority odorants. These "character defining" odorants appear to be dominated by compds. of relatively low volatility, high mol. wt., and high polarity. In particular, p-cresol alone appears to carry much of the overall odor impact for swine and beef cattle operations. Of particular interest is the character-defining odor impact of p-cresol as far as 16 km downwind of the nearest beef cattle feedlot. The findings are highly relevant to scientists and engineers working on improved air sampling and anal. protocols and on improved technologies for odor abatement. More research evaluating the use of p-cresol and a few other key odorants as a surrogate for overall odor dispersion modeling is warranted. (c) 2006 Preston Publications.
    13. 13
      Eaton, D. K.; Nielsen, L. T.; Wright, D. W. An integrated MDGC-MS-Olfactometry Approach to Aroma and Flavor Analysis. In Sensory Directed Flavor Analysis; Marsili, R., Ed.; Taylor and Francis Group LLC: New York, 2007; pp 81– 110.
      There is no corresponding record for this reference.
    14. 14
      Wright, D. W.; Nielsen, L.; Eaton, D.; Kuhrt, F.; Koziel, J. A.; Cai, L.; Parker, D. B. Animal Odor Assessment - Chickens, Pigs, Bats or Cats; it is Still Analytical Chemistry. In Proceedings of the National Poultry Waste Management Symposium; Springdale AK, USA, 23–25 Oct 2006.
      There is no corresponding record for this reference.
    15. 15
      Wright, D. W.; Eaton, D. K.; Nielsen, L. T.; Kuhrt, F. W.; Koziel, J. A.; Cai, L.; Lo, Y.; Parker, D. B.; Buser, Z. Synthetic CAFO odor formulation; an effective technique for validation of odorant prioritizations. In Proceedings of the Ecological Society of America Conference; Washington, DC, USA, 5–8 June 2006.
      There is no corresponding record for this reference.
    16. 16
      Wright, D. Application of multidimensional gas chromatography techniques to aroma analysis. In Techniques for Analyzing Food Aroma; Ray, M., Ed.; Marcel Dekker, Inc.: NY, 1997; Chapter 5.
      There is no corresponding record for this reference.
    17. 17
      Bulliner, E.A. IV.; Koziel, J. A.; Cai, L.; Wright, D. Characterization of livestock odors using steel plates, solid phase microextraction, and multidimensional - gas chromatography-mass spectrometry- olfactometry. J. Air Waste Manage. Assoc. 2006, 56, 1391– 1403,  DOI: 10.1080/10473289.2006.10464547
      17
      Characterization of livestock odors using steel plates, solid-phase microextraction, and multidimensional gas chromatography-mass spectrometry-olfactometry
      Bulliner, Edward A., IV; Koziel, Jacek A.; Cai, Lingshuang; Wright, Donald
      Journal of the Air & Waste Management Association (2006), 56 (10), 1391-1403CODEN: JAWAFC; ISSN:1096-2247. (Air & Waste Management Association)
      Livestock operations are assocd. with emissions of odor, gases, and particulate matter (PM). Livestock odor characterization is one of the most challenging anal. tasks. This is because odor-causing gases are often present at very low concns. in a complex matrix of less important or irrelevant gases. The objective of this project was to develop a set of characteristic ref. odors from a swine barn in Iowa and, in the process, identify compds. causing characteristic swine odor. Odor samples were collected using a novel sampling methodol. consisting of clean steel plates exposed inside and around the swine barn for ≤1 wk. Steel plates were then transported to the lab. and stored in clean jars. Head-space solid-phase microextn. was used to ext. characteristic odorants collected on the plates. All of the analyses were conducted on a gas chromatog.-mass spectrometry-olfactometry system where the human nose is used as a detector simultaneously with chem. anal. via mass spectrometry. Multidimensional chromatog. was used to isolate and identify chems. with high-characteristic swine odor. The effects of sampling time, distance from a source, and the presence of PM on the abundance of specific gases, odor intensity, and odor character were tested. Steel plates were effectively able to collect key volatile compds. and odorants. The abundance of specific gases and odor was amplified when plates collected PM. The results of this research indicate that PM is major carrier of odor and several key swine odorants. Three odor panelists were consistent in identifying p-cresol as closely resembling characteristic swine odor, as well as attributing to p-cresol the largest odor response out of the samples. Further research is warranted to det. how the control of PM emissions from swine housing could affect odor emissions.
    18. 18
      Lusk, L. T.; Murakami, A.; Nielsen, L.; Kay, S.; Ryder, D. Beer photooxidation creates two compounds with aromas indistinguishable from 3-methyl-2-butene-1-thiol. J. of the Am. Soc. of Brew. Chemists. 2009, 67, 189– 192,  DOI: 10.1094/ASBCJ-2009-0910-02
      18
      Beer photooxidation creates two compounds with aromas indistinguishable from 3-methyl-2-butene-1-thiol
      Lusk, Lance T.; Murakami, Aki; Nielsen, Lawrence; Kay, Susan; Ryder, David
      Journal of the American Society of Brewing Chemists (2009), 67 (4), 189-192CODEN: JSBCD3; ISSN:0361-0470. (American Society of Brewing Chemists, Inc.)
      Beer photooxidn. (lightstruck reaction) creates the well-known, intensely flavor-active compd. 3-methyl-2-butene-1-thiol (MBT). The sensory threshold in beer for this malodorous compd. is 2-7 ng/L. Using solid-phase microextn. and multidimensional GC-olfactometry, we discovered two previously unidentified compds. with aromas indistinguishable from the "skunky" or "foxy" aroma used to describe MBT. These addnl. skunky aroma compds. undoubtedly contribute to the overall lightstruck character in beer. Addnl., we discovered that MBT and one of the two other compds. slowly formed during beer thermal oxidn. in the absence of light.
    19. 19
      Torrice, M. The scientists who sniff water. Chem. Eng. News 2017, 95, 16– 19,  DOI: 10.1021/cen-09527-scitech1
      There is no corresponding record for this reference.
    20. 20
      Harbison, M. (adapted from Dredge, M.). Daily infographics; beer edition: The beer flavor and aroma wheel. Pop. Sci. (Web Ed.) 2013, 10. Available online: https://www.popsci.com/science/article/2013-01/infographic-day-beersci-edition-beer-flavor-wheel/ (accessed on 17 January 2022).
      There is no corresponding record for this reference.

  • Supporting Information

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    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.2c00517.

    • Table S1. Chronological summary of uncovering the link between 321MBT and “skunky” cannabis/hemp odor (PDF)


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