Thiol Driver 

Scientifically-driven Hoppy Lager Designed to Push Fruity Hop Thiols

O

ne of the reasons I love grinding through academic brewing papers is because sometimes findings from multiple studies can come together and inspire something new for me to try. This happens organically as I go down rabbit holes on unrelated topics and start connecting the dots. The great part about writing for the blog and my book is that it forces me to not only read the studies but try to explain them to others and think more broadly about how the results might be put into practice by brewers. This is exactly what happened when I was researching hop thiols for a chapter in the book. Looking at the findings from multiple papers, I suggested it might be worth experimenting with a hoppy lager with a dash of wine yeast for multiple science-based reasons, which this post explores. Since I suggested the experiment in the book, I thought I better take my own advice and give it a shot! Before getting into it, I first need to thank my good friend Spencer Love for helping me out with this batch, hopefully, we can team up on a few more brews for articles like this!

I have to admit something though. I’m not the biggest fan of lagers. It’s kind of a running joke at Sapwood if somebody brings in a lager (or something with lactose) it goes to Mike automatically. In fact, we just brewed our first lager at Sapwood, which doubled my career lager brew count total to two batches. Don’t get me wrong, I totally get the appeal for a well-brewed pilsner, for example. But, I’d always rather have something with hops, it’s just who I am : ) I even joked for a while that I wasn’t even going to mention the word lager in the book, but then the research had to spoil it for me as I got too excited about the potential for the lager brewed for this post, which is now appropriately named Thiol Driver.

What’s in this post? First I go through some of the research that inspired this particular brew, which will explain why the recipe was crafted as it was. Then the recipe and tasting notes for Thiol Driver follow the science discussion. Spoiler, it’s pretty good!

The Hop-Derived Ester 2MIB

Although studied slightly less in the literature, various esters from hops can impact final beer flavors and aromas just like hop thiols and terpenoids. One of the hop-derived esters that’s gotten some attention is 2MIB (2-methylbutyl isobutyrate) because of its ability to give a beer apricot-like flavors. ¹ 

So, which hop varieties have more of this particular ester? One paper brewed single-hopped beers in order to determine final 2MIB concentrations for different hop varieties used in the whirlpool. Only Southern Cross tested above the threshold (which is 78 ug/L). Other varieties that were below the threshold, but still had relatively high levels of 2MIB, were (in order from highest) Pacific Jade, Polaris, Huell Melon, Riwaka, and Waimea and could all be other varieties to play with for late hopping if trying to push the apricot-like ester.²

Yeast strains may also play a role in the final hop-derived ester concentrations, as one study looked at 2MIB in ale and lager fermentations. The results showed that a Pilsner fermented with a “standard lager yeast strain,” resulted in more 2MIB than the ale, which was fermented with an English strain. Although the increase wasn’t massive, the beers had the same dry hopping and the lager strain resulted in approximately a 17% 2MIB increase.³ This is exactly why I chose to ferment Thiol Driver with a standard lager yeast (S-23 SafLager German Lager).

A 2018 BrewingScience paper also looked at the role of two different yeast strains (WLP001 California Ale and WLP029 German Ale/Kolsch) and the concentrations of terpenes, esters, and thiols paired with early fermentation dry hopping. They dry hopped with either Cascade or Hallertau Mittelfrüh on day three of fermentation and then tested the beer for its compounds. The Kolsch strain in the study outperformed the ale strain in final 2MIB concentrations, which suggests it may also be a strain worth trying in a beer like this to push 2MIB.⁴ I would love to see follow-up testing with the lager strain used in Thiol Driver!

Synergy Between Hop Esters and Thiols

The synergy between compounds is another area of exciting hop research, particularly because researchers are finding that hop thiols can actually lower the taste threshold of fruity terpenoids. One such paper looking specifically at Nelson Sauvin, which is unique in that it’s rich in the thiol 3-sulfanyl-4-methylpentan-1-ol (3S4MP). The authors tested the possible synergistic impact of the thiol when dosed with other known hop compounds. Specifically, a solution with 40 ng/L (the threshold) of 3S4MP was compared to solutions with the same amount of 3S4MP in addition to other compounds (linalool, 2MIB, and geraniol), some below their thresholds.

Focusing on the paper’s findings as it relates to 2MIB, the authors found that the presence of the Nelson Sauvin thiol (3S4MP) actually enhanced the flavors of 2MIB, even though 2MIB was dosed below the threshold.⁵ This enhancement of flavor via synergy is interesting because it suggests that 3S4MP is acting as a flavor enhancer to 2MIB, boosting its flavor potential above the actual concentration.

The findings above are why Thiol Driver is hopped with Southern Cross in the whirlpool, potentially pushing the apricot-like 2MIB ester close to or above its taste threshold. Thiol Driver is then dry-hopped twice with Nelson Sauvin to impart its unique 3S4MP thiol which should even further push the sensory experience of 2MIB! 

Thiols and Fermentation Temperature

Although I go into much more detail regarding hop thiols and biotransformation in the book, here are the main three hop-derived thiols studied with their descriptors:

• 4MMP – Boxtree, ribes, and blackcurrants.
• 3MH – Grapefruit and gooseberry.
• 3MHA – Passion fruit and guava. 3MHA is converted from 3MH during fermentation with the right yeast strain that has been tested to produce β-lyase during fermentation. A commercial enzyme can also be used with normal ale strains (like Rapidase Expression Aroma).

Now, what’s of most interest to me regarding thiols and using a lager strain (in addition to the potential for more 2MIB) is a finding that lower fermentation temperatures may help to raise final hop thiol concentrations. Remember that lagers ferment at lower temperatures than ale strains. A paper that examined whether thiol concentrations increase or decrease based on fermentation temperature dosed test beers with Mosaic hops at the onset of fermentation (early dry hopping) and measured thiols 3MH and 3MHA. The authors found that almost twice the amount of 3MHA was measured in the beer fermented at 59°F (15°C) compared to the one at 71°F (21°C) with a wheat beer yeast (Tum 68).⁶

Specifically, the above paper found that the tropical and desirable 3MHA (which is converted from 3MH) went from 4 ng/l to 8 ng/l at the lower temperature. This might not seem like much, but with a low threshold for 3MHA (9 ng/l), you can see why it’s important. Also, because 3MHA is converted from 3MH, it’s equally important that the 3MH concentration also increased when fermented at the cooler temperature going from 31 ng/l to 37 ng/l. Obviously, the more you can push the 3MH the more potential for 3MHA (especially with the right yeast strain or with a commercial enzyme). The passionfruit leaning 3MHA thiol is one that I’m most excited about, so anything I can do to set the stage for it’s production I’m interested in trying.

The results above can be somewhat explained by a 2011 paper focusing on the aroma compounds in wheat beer when injected with CO2 at different temperatures (mimicking fermentation). The authors found that the polarity of the compounds played a role in the potential loss during fermentation. The more hydrophilic a compound, the more likely it will remain in the solution during fermentation and be less impacted by temperature increases.⁷ This makes sense as studies have shown that in beer and wine must fermentations volatile compounds are partly transported to the surface by CO2 and released into the gas phase. Because thiols have lower boiling points and are less soluble than other solvents like alcohols, you can see why they may be more impacted by increased fermentation temperatures.

Wine Yeast and Bioflavoring (VIN 7)

Ok, so if using a lager strain we might be able to push 2MIB levels (especially with Southern Cross in the whirlpool), dry-hopping with Nelson Sauvin might synergistically increase the perception of 2MIB, and fermenting at the cooler lager temperature might increase thiol concentration like 3MH, how can we try to increase the conversion to 3MHA? Enter wine yeast and their magical abilities to bioconvert! I’ve leaned heavily on wine research in this area of biotransformation of thiols because they have been looking at the topic for some time. Many of these same thiols we are interested in studying in hops are the same ones they are looking at in wines (mostly white wines).

One such study examined seven wine strains for their ability to release volatile thiols, including strains L2056, NTII6, VIN7, VIN13, VL3, X5, and QA23. The results showed that VIN7 released the second most 3MH and had the highest concentration of 3MHA, which was converted from 3MH.⁸ So I think we have our winner for Thiol Driver, I used just 8% VIN7 as part of a yeast blend with the lager strain, which is easy to do with dry yeast as you can just measure out the blend in grams. So now we are taking advantage of the cooler lager fermentation temperature for thiol retention and hopefully getting a greater release of thiols with the wine yeast, which also happens to work best at the cooler lager temperatures.

I purchased VIN 7 from Scott Laboratories (no association with me, this cracked me up at a recent conference, two people thought Scott Laboratories was a side project of mine). The problem is that it comes in 500-gram bricks, which is fine for me as I can put it to work at Sapwood, but homebrewers don’t need this much. You could get a brick as part of a homebrewer club and split it up amongst the members if it’s something you want to experiment with.

Here is the commercial description of VIN 7 :

“Ideal for the production of aromatic white wines at low temperatures. VIN 7 releases passion fruit, grapefruit, gooseberry and guava aromas and flavors from their non-aromatic precursors in the must. It is therefore especially recommended for vinification of the following grape varieties: Sauvignon blanc, Chenin blanc and Colombard.”

VIN 7 Specifics:

Temperature range: 13-16°C (55-61°F)
Killer: sensitive
Glycerol production: 5 – 7 g/l (medium range)

Thiol Driver Recipe 

  Brewed: July 2019

Results

Appearance: Beautiful light hazy gold. Tight, firm head with excellent retention and lacing.

Nose: Bitter gooseberry, pine, peach rings, the jelly inside a donut, crackery pilsner, oddly cinnamon-like when warmer. 

Palate: Bright hop front, but not super varietal specific, bold fuzzy stone fruit, grainy pilsner malt, tangy apple skin, mild lingering minerality but really clean, wheaty peach skin, long white wine palate (glycerol?). For the amount of Nelson used, it’s kind of crazy how not Nelsony it is which may be due to some of the bioconversions and synergy pushing the fruitier notes. Super happy with the creaminess of this low ABV lager and how the wine yeast didn’t get too expressive (In previous experiments I’ve gotten some phenolic flavors). 

Thoughts/Changes: Drinks really clean and fruity. Pils malt is a tad detracting personally (Spencer doesn’t love pilsner, thinks it can sometimes come across slightly soapy), lacks some complexity. Would potentially swap out for a full pound of malted rye for a deeper character, which might also play well on the back palate drying. There is a noticeable drying Epsom character but it works well. Certainly in no way catty. Drinks best a little warmer than most lagers (40-42 degrees). We went through this 5-gallon (20L) keg pretty quick, it was just so unique in a good way. I encourage people to experiment with this concept and let me know what you think!

Key Findings

• 2MIB (2-methylbutyl isobutyrate) is a hop-derived ester that can contributed apricot-like flavors. 
• Southern Cross produced the most 2MIB, but Pacific Jade, Polaris, Huell Melon, Riwaka, and Waimea are other high producers (but under the taste threshold). 
• A standard lager yeast strain resulted in more 2MIB than an English ale strain tested.
• The presence of the Nelson Sauvin thiol (3S4MP) enhanced the flavors of 2MIB, even though 2MIB was dosed below the threshold via synergy. 
• Some thiols may be retained in higher concentrations with lower fermentation temperatures. 
• VIN 7 wine yeast has a strong ability to enhance 3MH (grapefruit) and ultimately 3MHA (passionfruit) flavors.