exBEERiment | Fermentation Temperature: Imperial Yeast A44 Kveiking In A Blonde Ale

Author: Cade Jobe

While it’s been around for hundreds of years, the family of yeasts known as Kveik burst onto the mass brewing scene just few years ago due to attention given to it by Lars Marius Garshol and Milk The Funk. Hailed for its ability to produce clean beers when fermented in strikingly warm environments, Kveik has naturally been embraced by brewers who can’t control fermentation temperatures, though many who can prefer the characteristic fruitiness these yeasts are known to impart.

Recent xBmts have shown that tasters were able to reliably distinguish beers fermented at disparate temperatures with Imperial Yeast A43 Loki and Bootleg Biology OSLO, both of which are single Kveik strains isolated from different Norwegian sources. Recently, Imperial Yeast made year-round their once-seasonal A44 Kveiking, which is a blend of 3 Kveik strains they say “thrives in hot fermentations when big complex ester profiles are desired,” indicating it would perform differently at cooler temperatures.

Fermentation temperature is something I’ve taken seriously for most of the time I’ve been brewing, using the typical combination of a chest freezer and regulator to ensure my beers don’t get too warm. I was excited to see how fermentation temperature would affect beers fermented with Imperial Yeast A44 Kveiking and put it to the test!

| PURPOSE |

To evaluate the difference between a beer fermented with Imperial Yeast A44 Kveiking at a stable 75°F/24°C and one fermented in a range of 90-97°F/32-36°C in a warm garage.

| METHODS |

In hopes of emphasizing any differences caused by fermentation temperature, I designed a simple light ale recipe for this xBmt.

From Venus

After collecting the water for a 10 gallon/38 liter batch, adjusting it to my desired profile, and getting it over the flame, I weighed out and milled the grain.

Once the water was properly heated, I incorporated the milled grains then checked the mash temperature.

During the mash rest, I collected out the kettle hop addition.

When the 60 minute mash was complete, I sparged to collect the pre-boil volume.

The wort was boiled for 60 minutes.

Following the boil, I quickly chilled the wort with my IC before taking a hydrometer measurement showing it was at the expected OG.

After evenly splitting the wort between 2 sanitized Brew Buckets, I then placed both in my fermentation chamber to stabilize at the same 75°F/24°C pitching temperature. The following morning, I moved one of the fermenters into my warm Texas garage then pitched a single pouch of Imperial Yeast A44 Kveiking into each batch.

The beer fermenting in my garage reached a high of 97°F/36°C at 36 hours post-pitch and was sitting at a low of 90°F/32°C when FG was reached just 2 days later. I left the warm ferment beer in my garage for the 3 additional days it took the batch fermenting at a controlled 75°F/24°C to reach FG.

At this point, I moved the warm ferment beer into the chamber and cold crashed both under pressure to 32°F/0°C. I ended up letting the beers sit for a couple of weeks while I cleared up space in my keezer before racking them to CO2 purged kegs.

The filled kegs were placed in my keezer, burst carbonated, then left to condition for a week before they were ready to evaluate.

| RESULTS |

Due to social distancing practices as a result of the COVID-19 pandemic, data for this xBmt was unable to be collected in our typical manner. As such, temporary adaptations were made involving the author completing multiple semi-blind triangle tests in as unbiased a way as possible.

Utilizing 4 opaque cups of the same color where 2 were inconspicuously marked, one set was filled with the beer fermented at 75°F/24°C while the other set was filled with the beer fermented at 97°F/36°C. For each triangle test, 3 of the 4 cups were indiscriminately selected, thus randomizing which beer was the unique sample for each trial. Following each attempt, I noted whether I was correct in identifying the unique sample. Out of the 10 semi-blind triangle tests I completed, I needed to identify the unique sample 7 times (p<0.05) in order to reach statistical significance, which is exactly how many times I did (p=0.02), indicating I was able to reliably distinguish a light ale fermented with Imperial Yeast A44 Kveiking at 75°F/24°C from one fermented in my warm garage that ranged from 90°F/32°C to 97°F/36°C.

Despite knowing Kveik ferments cleanly at warm temperatures, I was admittedly nervous that the beer fermented in my warm garage would develop unpleasant esters that overwhelmed the subtler malt and hop character. Such was not the case! Both beers were surprisingly clean, allowing the malt and hops to come through nicely. While the beers were definitely similar, I did perceive more fruity esters in the one fermented warm, though it was unexpectedly very pleasant. I didn’t really have a preference for one over the other, as both were equally crushable in the Texas summer heat.

| DISCUSSION |

It’s widely believed that precisely controlling fermentation temperature is an important practice for producing quality beer, namely by restricting the amount of undesirable esters and phenols produced, as well as limiting fusel alcohols. While most manufacturers recommend ale strains ferment between 64-72°F/18C-22°C, Kveik is an oddity in that its recommended fermentation temperatures are much higher, upwards of 100°F/38°C, with many claiming poor, or at the very least, different performance at the cooler end of the scale. In support of this notion, I was able to reliably tell apart a beer fermented with Imperial Yeast A44 Kveiking at 75°F/24°C from one fermented in my warm garage, which ranged between 90°F/32°C to 97°F/36°C.

The mere thought of a fermenting beer getting warmer than about 72°F/22°C is enough to bring most brewers to the brink of a panic attack, yet such temperatures are viewed as too low for Kveik. It’s fascinating, and the evidence showing that crazy high temperatures produce clean fermentation character continues to pile up. While I did perceive the warm fermented beer in this xBmt as being slightly more fruity than the one fermented cooler, making it fairly easy for me to distinguish, I didn’t detect any flaws typically associated with poor fermentation temperature control in either.

Seeing that Imperial Yeast markets A44 Kveiking as producing fruitier characteristics when fermented at the warmer end of the scale, I view these results as confirmatory. I certainly plan on using this and other Kveik strains in the future, and I’m especially interested to see how adjusting the fermentation temperature range could alter the ester profile in more hop-focused styles.

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

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