Author: Matt Del Fiacco

One of the most discussed aspects of brewing, a variable many believe is of supreme importance when it comes to producing consistently good beer, is fermentation temperature. By precisely controlling the temperature of beer during the fermentation process, one is able to modulate the formation of both desirable and undesirable characteristics. Fermenting too cool is generally said to lead to a cleaner profile, which may or may not be preferred, but incites nowhere near the amount of fear and ire as the thought of fermenting too warm.

Unquestionably spurred by the incredible work of European beer researcher and blogger, Lars Marius Garshol, kveik yeast has grown massively in popularity over the last few years. A strain of Norwegian origin with a fascinating history, kveik yeast is in the S. Cerevesiae family, but unlike other ale strains, it has been shown to perform very well at temperatures as warm as 95°F/35°C, producing a pleasant profile with no perceptible off-flavors. Given all that’s required for adequate fermentation temperature control, it’s no wonder brewers find this unique yeast strain so appealing.

Numerous labs have released versions of kveik yeast to the public, many isolated from a strain that came from Sigmund Gjernes’ Voss farmstead. Last year, Imperial Yeast released A43 Loki as a seasonal strain, though due to its popularity, they recently announced it would be a year-round offering. Excited to put this heat tolerant fermenter through the paces, I designed an xBmt to see how it performs when fermented at different temperatures.

| PURPOSE |

To evaluate the differences between beers fermented with Imperial Yeast A43 Loki at either 64°F/18°C or 90°F/32°C.

| METHODS |

After chatting with Lars about this xBmt, I came to the conclusion I wouldn’t be able to stay true to a Norwegian Farmhouse Ale due to some process and ingredient (namely juniper) limitations. The recipe I designed was heavily inspired by some of the work Lars has done and simple enough to exemplify any impact of the variable.

Oh, I’m Staying In The Kitchen

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5 gal 90 min 24.6 IBUs 2.9 SRM 1.073 1.018 7.3 % Actuals 1.073 1.019 7.2 % Fermentables Name Amount % Pilsner (2 Row) UK 13.875 lbs 100 Hops Name Amount Time Use Form Alpha % Magnum 11 g 90 min First Wort Pellet 12 Hersbrucker 46 g 15 min Boil Pellet 2.2 Yeast Name Lab Attenuation Temperature Loki (A43) Imperial Yeast 79% 68°F - 98°F Notes Water Profile: Ca 54 | Mg 11 | Na 25 | SO4 81 | Cl 65 Download Download this recipe's BeerXML file

After collecting both sets of brewing water and adjusting each to my desire profile, I set the controllers to warm them to strike temperature.

As the water was heating up, I weighed out and milled the grain for each 5 gallon/19 liter batch.

Once strike temperature was reached, I incorporated the grist into the water and checked to ensure both achieved the same target mash temperature.

I took pH readings 15 minutes into each mash that showed both were identical, as expected.

During the mash rests, I prepared the kettle hop additions.

When each mash was complete, I removed the grains then boiled the worts for 60 minutes before chilling both with my counterflow chiller during transfer to fermentation vessels.

Hydrometer measurements revealed both worts were at the same target OG.

Equal volumes of wort were transferred to fermentation kegs that were placed in separate fermentation chambers, one controlled to 64°F/18°C and the other set to maintain a steady 90°F/32°C.

At this point, I made a couple starters of Imperial Yeast A43 Loki using leftover wort.

The worts were left to sit in their respective chambers overnight so that each would stabilize at the target fermentation temperature. I returned the following morning, approximately 14 hours later, and pitched the yeast starters.

Curious to see how things were progressing, I took hydrometer measurements after just 2 days of fermentation and found both beers were chugging along at a similar pace. After another week, I took a second set of hydrometer measurements showing that each beer had reached a final gravity of about 1.018.

At this point, I pressure transferred the beers to CO2 purged serving kegs and put them in my keezer on gas to force carbonate. After another week of conditioning, the beers were ready to serve to tasters.

| RESULTS |

A total of 25 people of varying levels of experience participated in this xBmt. Each participant was served 1 sample of the cool fermented beer and 2 samples of the warm fermented beer in different colored opaque cups then asked to identify the unique sample. While 13 tasters (p<0.05) would have had to accurately identify the unique sample in order to reach statistical significance, 15 (p=0.006) did, indicating participants in this xBmt were able to reliably distinguish a lightly hopped pale colored beer fermented with Imperial Yeast A43 Loki at 64°F/18°C from one fermented at 90°F/32°C.

The 15 participants who made the accurate selection on the triangle test were instructed to complete a brief preference survey comparing only the beers that were different. A total of 9 tasters reported preferring the cool fermented beer, 4 liked the warm fermented beer more, 1 person had no preference despite perceiving a difference, and 1 person felt there was no difference.

My Impressions: I attempted 4 semi-blind triangle tests and chose the odd-beer-out every time, which left me confident they were noticeably different. While the beers shared a rich maltiness and moderate noble hop character, I perceived the warm fermented version as having a more expressive fruity yeast character compared to the batch fermented cool. I was startled by how much I enjoyed both of these beers, and while the were different to me, I can’t claim to have preferred one over the other. And there’s no way I’d guess one of these beers fermented 26°F/14°C warmer than the other. On the record, I’m a kveik convert!

| DISCUSSION |

Fermentation temperature is one of the most focused on variables in brewing, as it’s believed to be a major player in flavor development and overall beer quality. The mere idea of fermenting a beer of north of about 70°F/21°C is enough to make most brewers shudder, yet many have been going even warmer with kveik strains with positive results. Interestingly, tasters in this xBmt were able to tell apart versions of the same beer fermented with at either 64°F/18°C or 90°F/32°C, indicating temperature plays a role in overall character when fermenting with Imperial Yeast A43 Loki.

However, a difference implies nothing about quality. With rare exception, most other yeasts would be expected to produce an undrinkable mess if fermented at 90°F/32°C. Not only was the warm fermented beer in this xBmt not bad, but it was actually quite delicious. While I perceived it as possessing a slightly stronger ester profile than the cool fermented version, this character was by no means overblown. What these results suggest to me is that Loki may be an ideal strain for those who may not have the ability to precisely control fermentation temperature, as well as brewer interested in coaxing various characteristics out of a single strain.

Thanks to numerous xBmts, I’m admittedly not nearly as rigid when it comes to fermentation temperature as I used to be, at least within specific contexts. However, my skepticism was certainly in place when I set my controller to 90°F/32°C for this xBmt, confident not only that tasters would be able to tell it apart from the cool fermented version, but that it likely wouldn’t taste very good. While my hunch about there being a difference was accurate, I’m happy to report I was dead-wrong about the beer’s drinkability– I loved it and look forward to playing with Loki much more in the future!

If you have any thoughts about this xBmt, please do not hesitate to share in the comments section below!

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