What Are Thiols in Hops? A Craft Brewer's Guide to Tropical Aroma and Sulfur Control

Polyfunctional thiols drive the loudest tropical notes in modern IPAs, but not all extraction methods treat them equally.

Tropical notes in beer aren’t just a trend anymore, they’re a baseline expectation and marker of quality. Within a craft beer market that shrunk in 2024, hazy and tropical-forward styles were among the few growing segments. According to Mintel’s 2025 US Beer Report, Sierra Nevada's Hazy Little Thing gained 6% volume year-over-year, and New Belgium's Juice Force grew 11.2%. Meanwhile, flavor profile ranks as a top purchase driver for 44% of Gen Z and 42% of Millennials.¹

Breweries like Highland Park with their TropicWeed IPA² or Varietal Beer Co and their experimental Mirrorshades IPA³ are building exactly the kind of tropical hop-forward profiles that consumers are chasing. What makes those beers work at the sensory level isn't just hop selection, it's a specific class of compounds called polyfunctional thiols. 

Understanding the risks and benefits of thiols is invaluable knowledge for any brewer right now. Hops produce hundreds of aroma-active compounds, but thiols are the ones responsible for the most intense tropical and citrus character in modern IPAs. Thiols register at concentrations far too low for most instruments to detect, yet your palate finds them immediately. The same chemistry that makes a thiol like 3S4MPA smell like passionfruit at trace levels also makes DMTS (dimethyl trisulfide) capable of ruining a beer at equal concentrations.

For craft brewers who want to build tropical hop character that's consistent, intentional, and free of sulfurous surprises, this is the chemistry worth knowing.

What Are Hop Thiols?

Polyfunctional thiols are volatile sulfur compounds (VSCs) that the human nose can register at concentrations significantly below the detection threshold of most terpenes. That kind of odor activity means a hop variety doesn't need high thiol concentrations to produce dramatic aroma impact. 

Structurally, thiols are sulfur-bearing molecules with a thiol group (-SH) attached to a carbon backbone. That’s what gives them both their potency and their tendency to go wrong under poor handling conditions. The same chemical sensitivity that makes 3S4MPA smell like intense Passionfruit at a few parts per trillion makes the broader VSC class capable of producing harsh off-notes at similarly low levels. This dynamic matters considerably when choosing and processing your hops. 

Hops aren't the only plant where these compounds drive aroma. Our analytical work first identified polyfunctional thiols as primary aroma contributors in cannabis.⁴ For example, you’ll find the same VSCs responsible for tropical and citrus-forward profiles in cultivars like Tangie and 24K Gold. That research established a shared analytical framework since hops and cannabis are both part of the Cannabaceae family and they express many of the same sulfur compounds.

Get a deeper look at the sulfur-driven chemistry shared between hops and cannabis in our white paper Defining Dank: From Countercultural Slang to Mainstream Flavor Phenomenon.⁵

Which Hop Thiols Create Tropical, Citrus, and Fruity Aromas?

Three polyfunctional thiols account for most of the tropical and citrus aroma character brewers associate with modern hop-forward styles. These thiols include: 

• 4-mercapto-4-methylpentan-2-one (4MMP)
• 3-sulfanyl-4-methylpentan-1-ol (3S4MP)
• 3-sulfanyl-4-methylpentyl acetate (3S4MPA)

4MMP registers at concentrations as low as a few parts per trillion and contributes blackcurrant, catty, and muscat grape character. It's the compound responsible for the sharp, almost savory pungency that defines certain dank hop profiles. Simcoe®, for example, has catty top notes that sit alongside resinous pine and tropical fruit.

The passionfruit and Grapefruit character present in many modern IPAs comes from 3S4MP and 3S4MPA. The former brings an intense passionfruit and grapefruit note with a faintly savory edge. Interestingly, 3S4MPA, which forms from 3S4MP during fermentation, skews toward grapefruit and rhubarb-like fruity freshness. 

Both are now understood to be more dominant than 3MH and 3MHA in many modern hop varietals. This pattern has become particularly apparent in varieties like Mosaic®, where 3S4MP drives the profile more than the thiols that earlier research emphasized.

How Biotransformation Unlocks Hop Thiols During Fermentation

Most of the thiols in raw hops exist as odorless precursors, or bound thiols. More specifically, they’re cysteine-conjugated compounds bound to amino acids that produce no aroma until something splits apart that bond. That something is yeast.

During fermentation, certain yeast strains express carbon-sulfur lyase enzymes that hydrolyze those cysteine-thiol bonds. This is what releases free aromatic thiols into the beer. The conversion rate is low, typically only a small percentage of available precursors become active thiols, but given that the sensory threshold for compounds like 3S4MP sits in the parts-per-trillion range, even a modest conversion produces meaningful aroma impact. 

Additionally, the yeast strain brewers select matters considerably here. 

Certain thiol-active yeast strains produce substantially more free 3S4MP and 3S4MPA than standard ale yeasts under identical conditions, and strain selection is increasingly treated as a formulation decision rather than a stylistic one.⁶

Dry hopping timing interacts with this too. Adding hops during active fermentation rather than after, sometimes called biotransformation in dry hopping, exposes precursors to yeast’s enzymatic activity at peak expression. This process can increase the percentage of free aromatic thiols compared to post-fermentation additions. The tradeoff is reduced control over which compounds get released and in what proportion.

This is where a characterized thiol-forward extract used alongside biotransformation adds something dry hopping alone can't provide. 

Biotransformation is inherently variable. The concentration of bound thiols can differ between hop harvests, thiol release rates vary between fermentations, and conversion efficiency changes with temperature. A cold-side addition with a known thiol profile applied after fermentation can layer precision on top of that variability. This allows brewers to anchor the tropical top notes of their beer regardless of what else fermentation delivered.

Grain vs. Hops: Where Do Thiol Precursors Actually Come From?

For most of brewing's modern history, thiol management meant hop management. The assumption was that flavor-active thiols originated from hop-derived precursors, biotransformed by yeast during fermentation. However, that assumption has since been revised.

Barley malt contains meaningful pools of cysteinylated and glutathionylated thiol precursors. Those happen to be the same compounds yeast acts on during fermentation. Research has identified and quantified these precursors across multiple malt varieties, and the numbers are striking. One study found that, at typical usage rates, a well-chosen base malt can contribute more hypothetical 3MH to a finished beer than a moderate hop addition at the same conversion rate.⁷

Treating the grain precursor pool as secondary to hop-derived thiol expression may be the wrong frame entirely. For brewers using high-biotransformation yeast strains, it may be the larger variable.

That said, grain-derived and hop-derived thiol precursors don't always produce identical flavor outcomes. The precursor type matters more than the source. Glutathionylated forms dominate in both grain and hops, and most standard ale yeasts primarily act on the less common cysteinylated fraction.

Which Hop Varieties Have the Highest Thiol Content?

Thiol content shifts by variety, region, and harvest year, which makes hop variety selection one of the most important formulation decisions a brewer makes when chasing tropical aroma. Whether those thiols are free or bound determines how much work the fermentation process will need to do and which tools will actually unlock them.

Which Hop Varieties Are High in Free Thiols?

Citra®, Mosaic®, and Strata® consistently show the broadest thiol profiles in published analysis. A 2024 study measuring free thiol content across hop varieties found these varieties ranking among the richest in both 3MH and 4MMP.⁸

Nelson Sauvin® is notable for its 3S4MP dominance specifically, making it one of the most thiol-distinct varieties in commercial brewing. Simcoe® and Summit™ carry significant 4MMP concentrations, which maps to the sharp blackcurrant and catty character those varieties are known for.⁹

Which Hops Contain the Most Bound Thiol Precursors?

Brewers and hop researchers have noted that varieties like Cascade and Centennial tend to carry more of their thiol content in bound precursor form, meaning their aromatic potential is largely inaccessible without active biotransformation.¹⁰ Several European varieties like Saaz, Hallertauer Mittelfrüh, and Perle show high bound precursor concentrations, particularly for 3MH precursors. This makes their aromatic potential somewhat dependent on biotransformation conditions resulting from yeast strain selection and mash hopping techniques.

A note on the data

Most published thiol analysis covers 3MH and 4MMP because those compounds have been studied longest. Newer analytical work, including research from Abstrax, points to 3S4MP and 3S4MPA as the more dominant thiol contributors to tropical aroma in modern varietals like Mosaic® and Nelson Sauvin®. Where older literature emphasizes 3MH, the sensory target is largely the same (e.g., passionfruit, grapefruit, tropical fruit intensity). However, the specific compounds responsible, and the conditions that preserve or destroy them, differ enough to change how you'd approach yeast selection, dry hop timing, and extract sourcing.

High thiol potential and clean thiol expression aren't the same thing. The varieties with the most intense aromatic upside can possess a broader volatile sulfur chemistry that includes compounds working against everything you're building toward.

What Causes DMTS in Beer and How the Right Extract Prevents It

DMTS (dimethyl trisulfide) is a volatile sulfur compound that registers as cooked cabbage, boiled vegetables, and dehydrated onion at very low concentrations. A beer doesn't need much of it to taste wrong.

In hops, DMTS traces back to S-methyl-cysteine sulfoxide (SMCSO), a sulfur-containing precursor that breaks down and regenerates during post-harvest storage. What makes it particularly difficult to manage is that reducing SMCSO during kilning doesn't eliminate the problem permanently. 

Research has shown that DMTS levels can reappear in stored hops over time as sulfur compounds continue transforming during storage.¹¹ That means a batch of hops that tested clean at harvest can still end up carrying meaningful DMTS by the time it reaches your brite tank.

That storage dynamic becomes a permanent problem the moment any hop material is added post-fermentation. During active fermentation, volatilization and CO2 scrubbing continuously strip low-threshold compounds from the beer. Once fermentation is complete, that pathway closes. Any DMTS introduced through a cold-side addition via dry hops or extract has nowhere to go. It accumulates in the package as the beer ages, producing off-notes that no amount of conditioning will fix.

When it comes to hop extracts, the extraction method used will determine how much DMTS ends up in the final extract. Steam distillation and CO2 extraction, the two most common commercial methods, tend to generate or concentrate DMTS during processing. 

For example, in a blind sensory panel conducted by Abstrax researchers comparing three Citra-based extracts, a steam-distilled sample produced strong cabbage, meaty, and dehydrated onion descriptors. A CO2-extracted sample showed lower but still detectable cabbage and spicy off-notes. Quantum Series Citra®, produced using our proprietary extraction process, showed negligible DMTS by GCxGC-SCD analysis and was described by panelists as hop-like, citrusy, and fruit-forward, with no detectable sulfur defects.

Want the full breakdown of how extraction methods affect DMTS levels? Get all the chemistry and sensory data details in our white paper Defeating DMTS: How Quantum Extracts Prevent Flavor Defects.¹²

How Craft Brewers Can Use Hop Thiols in Formulation

When used together, biotransformation and cold-side additions cover different parts of the thiol picture. Biotransformation unlocks what's latent in your hop additions during fermentation, while a characterized cold-side extract brings a known thiol profile that stays consistent batch to batch regardless of precursor variability or yeast performance.

For brewers building tropical or citrus-forward profiles, the Quantum Series offers varietal-specific hop extracts with thiol-rich character that can be dialed in at the brite tank. 

We already know that dank Simcoe covers the 4MMP register with sharp, catty, blackcurrant-adjacent notes that sit underneath tropical fruit. However, brewers who want musky Passionfruit, Grapefruit, and Pineapple character that intensifies cleanly without the sulfur baggage should reach for Galaxy® and Nectaron®. They have some of the richest expressions of 3S4MP and 3S4MPA-driven aroma in the entire Quantum collection.

For brewers who want something brighter and more citrus-forward rather than dank, Motueka® and Riwaka™ offer a unique entry point. The mojito-like Lime and zesty Lemon character in Motueka® pairs well with thiol-forward additions in lighter styles where passionfruit and grapefruit could overwhelm. Riwaka™ leans toward pink grapefruit with herbal, dank undercurrents. That feature is useful for bridging citrus and dank registers in the same bill without the need for separate additions.

These distinctions matter more in formats where hop aroma carries the entire sensory experience. In NA beer and hop water, there's no ethanol to soften off-notes or malt sweetness to provide contrast. A poorly chosen extract can introduce DMTS into a product with no safety net. 

A well-chosen extract applied cold-side with a clean thiol profile can produce tropical aroma intensity that rivals traditionally dry-hopped beer. And it can do so without the oxygen exposure, beer loss, or batch-to-batch inconsistency that comes with heavy dry hop loads.

Practical Formulation Notes on Thiols for Craft Brewers

Thiol expression is sensitive enough that small process decisions compound quickly. With that in mind, here are a few things worth building into your SOPs before the next batch:

• Choose your yeast with thiol release in mind. If tropical and citrus-forward character is the target, strain selection is as important as hop selection. Thiol-active strains express significantly higher carbon-sulfur lyase activity than standard ale yeasts, which translates directly into more free 3S4MP and 3S4MPA in the finished beer. Before assuming that dry hopping is the limiting variable, it’s essential to know what your house strain is actually doing to your precursor pool.

• Dry hop timing affects thiol yield, not just aroma character. Additions during active fermentation expose cysteine-conjugated precursors to peak yeast enzymatic activity. Post-fermentation additions don't. If your thiol expression is consistently falling short, timing may be the variable to adjust before hop rate.

• Cold-side additions work best when fermentation has done its job first. A cold-side extract with a known, consistent thiol profile applied at the brite tank anchors your top notes with consistency, but it performs best layered over a fermentation profile that has already done its biotransformation work. Think of it as locking in a ceiling, not compensating for a floor.

Some brewers find that earlier additions create unexpected but welcome transformations. The right call depends on your format and your vision for the end-product.

• In NA beer and hop water, your DMTS tolerance is effectively zero. Without ethanol or residual sweetness to mask off-notes, any sulfur defect introduced after fermentation will be immediately apparent to the consumer. Extract quality in these formats isn't simply a formulation preference, it determines whether the product is sellable.

• Source matters as much as variety. Two extracts from the same hop variety produced by different methods can deliver dramatically different thiol profiles and DMTS loads. GCxGC-SCD analysis of the extracts you're evaluating is the only way to know what you're actually adding to your beer.

Partner with Abstrax for Consistent Hop-Forward Profiles

Our team of analytical flavor chemists has spent years mapping the VSC chemistry of both hops and cannabis, and that research foundation is built directly into every Quantum Series extract. No DMTS. No sulfur guesswork. Just clean, varietal-specific hop character you can dial in cold-side with the same precision every batch.

The Quantum Series gives brewers precision-extracted hop profiles with none of the sulfurous off-notes that plague traditional cold-side additions. And if you're growing or sourcing your own hops, our Toll Processing service lets you lock in that aroma profile at harvest before storage has a chance to work against you.

If you're ready to start benchtop testing or want to talk through your formulation goals, contact us today and let's get to work.

References

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2. Highland Park Brewery. (n.d.). Highland Park Brewery: Los Angeles beer, food, and wine. Retrieved [April 29, 2026], from https://hpb.la/ 

3. Varietal Beer Co. (n.d.). Varietal Beer Co. Retrieved [April 29, 2026], from https://varietalbeer.com/ 

4. Oswald, I. W. H., Paryani, T. R., Sosa, M. E., Ojeda, M. A., Altenbernd, M. R., Grandy, J. J., Shafer, N. S., Ngo, K., Peat, J. R., III, Melshenker, B. G., Skelly, I., Koby, K. A., Page, M. F. Z., & Martin, T. J. (2023). Minor, nonterpenoid volatile compounds drive the aroma differences of exotic cannabis. ACS Omega, 8(42), 39203–39216. https://doi.org/10.1021/acsomega.3c04496 

5. Abstrax Hops (2026). Defining Dank: From Countercultural Slang to Mainstream Flavor Phenomenon. [White paper]. Retrieved April 28, 2026 from https://cdn.shopify.com/s/files/1/0743/6337/1815/files/Abstrax-Defining-Dank-White-Paper-WEB.pdf?v=1773182663 

6. Svedlund, N., Evering, S., Gibson, B., & Krogerus, K. (2022). Fruits of their labour: Biotransformation reactions of yeasts during brewery fermentation. Applied Microbiology and Biotechnology, 106, 4929–4944. https://doi.org/10.1007/s00253-022-12068-w 

7. Roland, A., Delpech, S., Viel, C., Reillon, F., Schneider, R., & Dagan, L. (2016). First evidence of cysteinylated and glutathionylated precursors of 3-mercaptohexan-1-ol in malts: Toward a better aromatic potential management? [Conference poster]. World Brewing Congress, Denver, CO, United States. 

8. Liu, Y., Dancker, P., Biendl, M., & Coelhan, M. (2024). Comparison of polyfunctional thiol, element, and total essential oil contents in 32 hop varieties from different countries. Food Chemistry, 455, 139855. https://doi.org/10.1016/j.foodchem.2024.139855 

9. Holt, S., Miks, M. H., de Carvalho, B. T., Foulquié-Moreno, M. R., & Thevelein, J. M. (2019). The molecular biology of fruity and floral aromas in beer and other alcoholic beverages. FEMS Microbiology Reviews, 43(3), 193–222. https://doi.org/10.1093/femsre/fuy041 

10. Lee-Weitz, G. (2023, February 28). Top hops for thiols. Hop Culture. https://www.hopculture.com/top-hops-for-thiols/ 

11. Peppard, T. L. (1978). Dimethyl trisulphide, its mechanism of formation in hop oil and effect on beer flavour. Journal of the Institute of Brewing, 84(6), 337–340. https://doi.org/10.1002/j.2050-0416.1978.tb03903.x 

12. Abstrax Hops. (2025). Defeating DMTS: How Quantum Extracts Prevent Flavor Defects. [White Paper]. Abstrax Hops. Retrieved April 28, 2026 from https://cdn.shopify.com/s/files/1/0743/6337/1815/files/Abstrax-Hops-Defeating-DMTS-Quantum-Case-Study.pdf?v=1751983258