Tuesday, May 16, 2023

Are Thiols a Scam? Thiolized Yeast, Phantasm, and the Rise of Designer Beer

Thiols are the coolest thing in brewing hoppy beers since the invention of dry hopping. It seems like almost every collab Sapwood Cellars has been invited to brew over the last 18 months ends up "Thiolized": 3S4MP (Cosmic Punch IPA with Phantasm and Nelson Sauvin at Fidens), Cone Concentrate (Cosmic Punch DIPA with Simcoe at Other Half DC), Celestial Paradox (London Tropics IPA with Strata/Galaxy/Citra/Simcoe at Toppling Goliath), Yasokeee (Helio Gazer DIPA with Peacherine, Hydra, and Phantasm at Cushwa), and most recently Heisenberg (Helio Gazer DIPA with Galaxy/Nelson at Commonwealth).

So why all of the excitement from our fellow craft brewers? Obviously many of the collab requests are due to Scott's writing about and advocacy for thiols, but are they just something new that will be passé soon, or are these strains here to stay?

What Are Thiols?

Thiols are sulfur-containing compounds that are often potent aromatics. The ones brewers are excited about are tropical, winey, and citrusy, while other thiols are intensely unpleasant with aromas of garlic or rotten eggs... which is why the thiol mercaptan is added to natural gas to alert people to leaks. The "skunky" aroma of light-struck beer is also 3-methyl-2-butene-1-thiol.

Unlike many other beer aromatics that require concentrations in the ppm (parts per million) or ppb (parts per billion) many thiols have an aroma threshold in the range of 5-70 ppt (parts per trillion). This means that it doesn't take much of them to be apparent, but also means that it doesn't require "high" concentrations to become dominant. 

In terms of positive beer and wine aromatics, the thiols that get the most attention are 4MMP, 3MH, 3MHA, and 3S4MP. These have perceptions that range from passionfruit, to grapefruit, to rhubarb. These are the intense aromatics that give New Zealand Sauvignon Blanc wines their distinct aromas and are found free at low-levels in many New Zealand hops (as well as some other varieties from around the world).

Most of the thiols found in hops, malt, and other botanicals are bound and thus not active aromatically. Enzymes are required to free them. There are wine strains available capable of this, but getting those genes into brewer's yeast requires more work. 

Where Do Thiols Come From?

Bound thiols are found in both malt and hops, but levels vary widely. The bond in need of breaking comes in two "flavors" Cysteinylated (Cys) and Glutathionylated (Glu). The vast majority (90%+) in both malt and hops is Glu. The IRC7 gene in certain wine strains and Omega's Cosmic Punch can only work on the less common Cys. As a result, mash hops are most potentially beneficial for Cosmic Punch, as the enzymes in the mash (especially in the acid-protein rest temperature range) can help convert Glu to Cys. Luckily some less expensive hop varieties have the highest levels of bound thiols. We've used Saaz, Cascade, and Calypso with good results.

The more intense strains like Berkeley Yeast Tropics line and Omega's Helio Gazer, Star Party, and Lunar Crush can simply be added to a standard recipe with or without whirlpool hops. Rather than having more copies of the IRC7 gene, they have a wholly different gene which can free Glu-thiols directly. The IRC7 gene in Cosmic Punch is "sourced" from yeast, while patB Omega uses in the more assertive strains is from a bacteria (if transgenic CRISPR/Cas9 gene modification is a step too far for you). We fermented a kettle sour which only had a small dose of hexalone (isomerized hop extract for head retention) with London Tropics. The result was intensely passion-fruity, so much so that it could almost pass a fruit beer. 

GM (genetically modified) yeast strains aren't allowed in commercial beers in many countries (e.g., Canada, New Zealand). As a result there are labs working with wild isolates capable of freeing thiols for co-fermentations (e.g., CHR Hansen - it is primarily marketed for NA beers) and breeding strains with heightened thiol freeing capabilities (e.g., Escarpment). Omega initially worked on yeast breeding between English ale and a wine strain capable of freeing thiols... our trials with it (Designer Baby) were interesting, but had too much of the wine strain's idiosyncrasies present (poor flocculation especially). 

Pros & Cons of Thiol-Expressing Yeast

-Intense aromatics that are otherwise impossible to achieve from hops, malt, and yeast
-Thiols have incredibly low aroma thresholds... measured in ppt (parts per trillion)
-Thiols are "free" no expensive hops or fruit required
-Thiols may help increase shelf-life by scavenging oxygen

-Higher perceived "sulfur" aromatics are frequent in thiol-freeing strains
-Some brewers/consumers/countries prefer to avoid GM ingredients
-Thiols can be "one note"... is it really that different from adding a jar of passion fruit extract?
-Repitching the yeast doesn't make as much sense if you also want to brew English Ales, Porters/Stouts etc. 

More isn't (always) Better

Initially there was a focus on maximizing thiol concentration. This could include colder fermentation temperatures, mash hops, and engineering strains with more assertive genes. Like most aspects of brewing (or cooking) maximizing a single flavor compound doesn't usually result in the best overall flavor or balance. 

Thiols aren't typically a "primary" aromatic in beer, so a beer with over-the-top thiol concentration without anything to play off of can taste artificial. On the other hand, some of our heavily dry hopped DIPAs have tested at over 100X the flavor threshold for 3MH and still weren't the primary aroma thanks to competition from the "traditional" hop aromatics. From those test, I wouldn't worry about dry hopping removing all of the thiols.

As a general rule, I'd suggest using a more restrained approach to thiols in lighter/cleaner/simpler beers. It doesn't take much to add a unique twist to a lager or American wheat, where a double-dry-hopped DIPA or fruit beer may benefit from a much higher amount. In the end it's about your palate and goals for a beer. 

In my experience expressing thiols doesn't make every hoppy beer better. They add a distinct note that can greatly enhance the perception of passionfruit-type aromatics. That is a wonderful contribution when you are leaning into those flavors, but can be distracting or muddle other flavors. For example, I love the "mango popsicle" aroma of great Simcoe. However, with one of the intense strains like London Tropics or Helio Gazer in an all-Simcoe beer can become more generically "tropical" rather than varietal "mango." On the other hand, when dry hopping with passion-fruity Galaxy, or brewing with actual passionfruit the thiol note helps to enhance the existing aromatics. 


Hand-in-hand with thiol-expressing yeast goes Phantasm. It is essentially the dried and powdered remnants of the highest-thiol New Zealand Sauvignon Blanc grapes. As a result it comes with a high price-tag of ~$35/lb. It really doesn't smell like much before fermentation. Added to the whirlpool it adds a huge amount of bound thiols for the yeast to work on. 

During fermentation I detect a distinct "white grape" flavor and aroma that I don't get from other thiol-expressing ferments that rely on grain and hops alone for bound precursors. A lot of this drops out with the yeast however and the finished beers are rarely as distinct. To my palate the added expense is hard to justify in a highly-dry-hopped beer where the thiols are competing against other big aromatics. Unless you lean into those aromatics with a hop like Nelson Sauvin. I like Phantasm best when it is paired with actual white wine grapes, or in a simple base where it can star. 

We haven't used Berkely Yeast's "Thiol Boost" additive yet... but I'm just not that excited about a 15X increase on the already intense London Tropics level of 3MH. I'd be interested in herbs or additives that could push other unique thiol aromatics that we aren't getting from grain/hops. 

My Favorite Thiolized Batches

At Sapwood Cellars, we've brewed a few dozen batches between Cosmic Punch, London Tropics, Lunar Crush, and experimental isolates. I've enjoyed most of them, but a handful stand-out as beers I loved!

Cosmic Rings: Galaxy and Citra is one of our favorite combinations... but we have had a difficult time sourcing great Galaxy (that doesn't taste like honey roasted peanuts). This all-Citra double-dry-hopped pale ale starts with New Zealand Taiheke (Cascade) in the mash and kettle. It's one of our favorite whirlpool hops because it is low alpha acid and has a beautiful tropical aroma... not to mention a lower price compared to other New Zealand varieties like Nelson Sauvin and Riwaka. Then we ferment with Omega's Cosmic Punch which brings some tropical aromatics without becoming distracting or artificial. Finally we dry hop with Citra and Citra Cryo at a combined 3 lbs/bbl.

Tropical Pop: Kettle sour fermented with Berkeley Yeast London Tropics along with passion fruit and mango purees. Passion fruit is expensive, fermenting with London Tropics boosted the passion fruit aroma allowing us to use less without sacrificing the aroma intensity.

Field Learning: As a homebrewer I loved being able to dump a bottle of thiol-rich New Zealand Sauvignon Blanc into a keg of mixed-ferm saison. That wouldn't be legal commercially, but what we did for this collab with Bissell Brothers was to brew a restrained base with Hallertau Blanc in the mash and Phantasm in the whirlpool and age it in fresh Sauvignon Blanc barrels along with Bissell's house culture. After a year we added fresh Chardonnay grapes from Crow Vineyards here in Maryland. The tropical notes from the thiols survived barrel aging and gave the beer depth we wouldn't have gotten from grapes and barrel alone.


Are thiols a scam? No, but they also aren't an innovation that fundamentally changes what it takes to make a delicious beer. Consider a thiol-freeing yeast when additional passionfruit-type aromatics will enhance your beer. Don't worry about maximizing the thiols unless you they will be competing against other strong aromatics. 

I suspect that this is just the lead in to even more exotic genetically modified yeast strains (we have a pitch of Berkeley's Sunburst Chico which is modified to express high levels of pineapple-y ethyl butyrate). If you can produce a flavor compound without the cost, environmental impact, variability of growing it I suspect the economic pressures will be too great! That said, making delicious beers isn't about maximizing one or two compounds (in the same way that vanilla flavoring is inexpensive, but doesn't fully replace the depth and complexity of real vanilla beans). 

Tuesday, April 25, 2023

Lessons from Five Years of Bugs, Barrels, and Brewing

This July marks five years since I left my day job with the federal government to brew full-time. We filled our first barrel with mixed-fermentation saison before opening the tasting room at Sapwood Cellars. Since then, we are up to 80 oak barrels with a dedicated suite for mixed-fermentation. So, I thought it would be a good time to sit down and reflect on the lessons that Scott and I have learned over the years! The things we got right, the things we got wrong, and where we are going from here!

Luckily, we've had a pretty good run so far! We've cultivated a great group of supporters in our Wood Club. Neologism (gin-barrel-aged Cascade/Simcoe Cryo dry-hopped pale sour) was named one of Craft Beer & Brewing's Top-20 beers of 2022 by way of winning a massive blind tasting. Despite the pandemic we've been able to modestly expand (production, staff, and space)! We're even shipping beers around the US through Tavour!

I recently realized that Google discontinued Feedburner in 2021... which is why you haven't gotten an email from me in a while. I've changed The Mad Fermentationist over to a new email service, so if you've signed up you should get emails for new posts going forward! If you want more emails from me, I write the near-weekly Sapwood Newsletter (with details on new beers often including info on ingredients, process, and equipment)!

The Things We Got Right

Diverse Microflora - It is certainly simpler to have a single "house" culture. It allows for relatively worry-free blending, but doesn't leave as much room for unique flavors. Maintaining multiple cultures, we have to worry about the microbes from one barrel over-attenuating in the bottle if they are more attenuative than others in the blend. However, the variety of flavors expressed and the options for blending is worth the effort at our scale. We've been even happier since we started selecting our favorite barrels and using them to inoculate subsequent batches. Now we can select which character fits a pale sour vs. a sour red. 

Last week we blended our second batch of Growth Rings (three year blend). To ensure all the microbes have time to get to know each other, we blended the four barrels (all different pale base beers) into a tote. They'll sit there for a couple months to ensure the gravity is stable before priming and bottling. 

Balancing Planning and Creativity - We started 2023 with a rough timeline of the 20 or so barrel-aged mixed-ferm we'll release. However, when we fill barrels there generally isn't a specific plan for which barrel will be in which beer. Pale, wine-barrel-aged beer can be delightful on it's own, or serve as a great base of fruit, herbs, or dry hopping. When we taste them, we get to decide what will make the best possible beer. However, it's also nice to have unique bases/barrels earmarked for a particular purpose. Some examples of those include Opulence (sour red with dried sour cherries in the bourbon and red wine barrels), a Brett'd Belgian Tripel in Calvados (apple brandy), or Port barrels for There Are No Edges (Vin de Céréale).

Tracking Barrels - Using Google Sheets has worked out well for us. I can sort based on fill date, final gravity, base beer etc. It allows me to sit on my couch at home and look at what beers we have in need of fruit, blending, packaging etc. Barrels still fall through the cracks (nothing is more heartbreaking than tasting a barrel that is old/stale and seeing a note about how good it was six months ago). Sometimes a beer is delicious, it just doesn't fit into a blend.

Blending with Others - Whether it is our tasting room manager (Spencer), Lead Brewer (Ken), homebrewing friends, fellow brewers (e.g., the brewers from Other Half for a collab) etc. Tasting barrels with other people helps improve your palate, riff on ideas, and make more broadly appealing results. We all have flavor "blind spots" and it is a good idea to have other people looking too. It's fun to riff off other people's ideas and come up with flavor combinations that neither of you would have made on your own. 

Packaging - Our general approach to packaging has been a big success... once we started measuring the dissolved CO2 in the beer rather than relying on time/temperature/pressure. We blend barrels or transfer fruited beers to our blending tank and cold crash. The day before bottling we'll push in sugar (boiled in water) along with Premier Cuvee champagne yeast (rehydrated with a small amount of Start-Up/GoFerm nutrient). We then carbonate the beer to ~2 vol of CO2, with the sugar and yeast taking the beer the rest of the way. We fill on a bottler (XpressFill) that purges and counter-pressure fills. So far it's resulted in relatively quick/clean refermentations with reliable carbonation. 

The Things We Got Wrong

Not Allocating Time - It is easy to put-off barrel-aged beers for more pressing concerns. When there are DIPAs to dry hop, Pilsners to can, and excises taxes to exercise the sour beers are often pushed to the side. It's rare that a week or two of aging in one direction or another makes a dramatic difference... but it's hard to get the most out of a barrel program if it is always at the bottom of the priority list. We're getting better at it, but I still wish from the start I'd blocked off a specific time/day each week to taste barrels, trial blends, source ingredients, prop microbes etc. 

Over-Correcting - Initially we weren't getting enough acidity in some of our beers, so we started pulling levers... colder rinsing barrels, lower hopping rates etc. Then our beers started becoming too sour, so we started veering back in the other direction. Managing a barrel program is like driving a cruise ship, it is difficult to pivot quickly! It's difficult to step back and tell if there is something causing one specific batch from being too sour (or not sour enough) or if there is a systemic issue. 

I think we would have been well served to do a better mix starting early (some barrels cold or no-rise, more with just Brett etc.). This would have given us more options when it came to blending over- or under-soured beers. 

Appreciating the Impact of Fruit On Acidity - Early on to help out some of those under-acidified beers, we went onto fruit. I was surprised how little additional acidity they picked up from refermentation. Sure adding a really acidic fruit (e.g., black currants for Fellow Feeling) contributed acidity, but just refermenting on wine grapes or peaches did not. However, as our cultures "matured" we suddenly had beers dropping from a tart pH of 3.5 to an obnoxiously-acidic 3.0 after going onto the fruit (2.8 pH was the lowest I measured). That's despite pitching rehydrated wine yeast to ensure a healthy and quick refermentation. 

I thought maybe our resident lactic acid bacteria were becoming more hop tolerant, and the dilution of the beer with fruit was allowing them to kick into action. To test this we began adding a small amount of hop extract with the fruit (we use a 20% alpha extract from Hopsteiner). Our fruited beers stopped dropping pH nearly as much, and as an added benefit the head retention improved considerably. 

Hot Side Hopping - I didn't appreciate how much of the classic funky lambic/saison profile originates with the hops. While we've always used a "restrained" dose of aged hops at the start of the boil (~.5 lbs/bbl), that just wasn't enough to give the beers the aromatic depth I was looking for. Recently we've been experimenting with a similar size whirlpool addition of cold-stored hops. So far the results are promising! I should have noticed that many of my favorite homebrewed Brett Saisons had big whirlpool additions and/or dry hopping... but those were all relatively quick turn-around and not barrel-aged. I'm glad Scott and Ken pushed to age some of our pale ales (pre-dry hopping) in barrels, an idea I wasn't excited about... but the results have been really delicious!

Where We Are Headed

Barrel-aged sour beer seems to be a wide/shallow market at the moment. The people who love them are still searching them out, but the average beer drinker seems to have moved on to less "challenging" more "reliable" styles. It's hard to know how much the rapid expansion of the segment played into this loss of interest. I've heard of quite a few breweries down-sizing or eliminating barrel-aged sour beers... Luckily we still have 150 people in our Wood Club, which is a great way for us to get these beers into the hands of our biggest supporters and a base-level of sales for eight releases a year. We're aiming to make our mixed-ferm beers more "delicious" the sorts of beers that people want to drink a whole bottle of, not just drink an ounce or two at a share. 

However, as we've ramped up the mixed-ferm bottle release schedule (2019 - 8, 2020 -11, 2021 - 13, 2022 - 16, and hopefully ~20 in 2023) we occasionally have bottles to spare. Rather than distribute them locally, we've partnered with Tavour (which ships to many states).  They just released Homegrown Rule, a "Marylanbic" base with homegrown lemon verbena (from my yard) and pineapple sage (from Ken's garden). It's tart and snappy, with plenty of our house microbe character, augmented by the citrusy-green notes of the herbs.