Comparing kveik to 'American Ale': the big deal
This post is the culmination of the work that we've been doing on kveik. The initial objective was to determine how temperature impacts fermentation performance in various kveik yeasts. The overall goal, however, was to compare kveik to modern American Ale yeast to learn how the different yeast pitching practices may have impacted the physiology and evolution of the different yeasts. Traditional farmhouse brewing practices in Norway included pitching kveik yeast into 'warm', strong wort (>28ºC, >17ºP) and storing the yeast dry for prolonged periods between brewing (up to a year). Contrast this with modern commercial brewing where American Ale yeasts like 'Chico' are repitched often (without prolonged storage) into relatively 'cool' and standard strength wort (around 18-20ºC, 12ºP). The hypothesis is that these differences in use over many generations have led to different adaptations.
Our work has shown that kveik yeasts have a temperature optimum ranging from ~33.5ºC (Omega Lutra and Escarpment Laerdal) to 37ºC (Lalbrew Voss). We also know that wild Saccharomyces cerevisiae yeasts have a temperature optimum ranging from ~31.5ºC to ~35ºC. So the next step was to compare the kveik yeasts to American Ale yeast and see if there is a difference. We chose SafAle US-05 as the prototype 'American Ale' yeast. And like before we tested the fermentation performance of US-05 in a standard wort at 8 temperatures (20ºC, 25ºC, 28ºC, 30ºC, 33.5ºC, 37ºC, 40ºC, and 42ºC) in triplicate. I used the same exact recipe and process that I used for all of my previous kveik 'test' ferments.
I have to admit I was pretty excited to try and ferment at 40-42ºC with US-05.
**The figures/data in this blog post were first available in our preprint on kveik temperature adaptations: https://biorxiv.org/cgi/content/short/2021.06.15.448505v1**
Here is my recipe and process.
----
60% Pilsner malt
38% Vienna malt
2% Munich malt
Mashed at 65ºC for 1 hour, 78ºC mashout for 1 min, batch sparge
Mash pH of 5.45-5.5 (to match the 'higher' mash pH of the kveik test ferments)
OG ~1.051
FG ~1.010-1.043 (!!)
60 min boil
23 IBU Hallertau magnum at 60 min
1/4 a teaspoon wyeast nutrients at 10 min
0.7 IBU Hallertau Mittelfrueh at flameout
Chilled to 20ºC, 25ºC, 28ºC, 30ºC, 33.5ºC, 37ºC, 40ºC, 42ºC using immersion chiller
Aerated with a 5 micrometer stainless steel airstone (air) for 4 minutes
Pitch rate: 1 L starter per ~2.5 gallons (close to standard recommended pitching rate)
Fermented at the respective pitch temps: 20ºC, 25ºC, 28ºC, 30ºC, 33.5ºC, 37ºC, 40ºC, 42ºC.
I maintained temperature using a fridge fermentation chamber for my fermentation vessel coupled to an inkbird and heating pad. This allows temperature control of +/- 0.5ºC from 4ºC to 42ºC.
Once the fermentations finished, I transferred each beer to a corny keg (2.5 gallons) and carbonated to 2.5 volumes.
--
Figure 1 Panel A from https://www.biorxiv.org/content/10.1101/2021.06.15.448505v1
Influence of temperature on the general fermentation performance of SafAle US-05.
Figure 1 shows the specific gravity of triplicate fermentations at 20-42ºC for SafAle US-05. In shades of blue we have 20ºC to 30ºC, in green 33.5ºC, in yellow 37ºC, orange 40ºC, and in red 42ºC. Fermentation is much slower to begin than with any of our tested kveik strains; we do see a ~2-5 gravity point drop in the first 6 hours (highest activity at around 33.5ºC and lowest activity at 20ºC). Nevertheless, 2-5 gravity points isn't bad for US-05 in just 6 hours!
Temperature has a large initial impact on viability and activity of US-05. At 42ºC & 40ºC, there is some initial fermentation activity but it quickly stops. This indicates that the cells aren't growing, there is just a bit of residual fermentation from the initial pitch but no growth or further activity. At 37ºC, US-05 absolutely struggles but does manage to ferment down to around 1.030 (~40% apparent attenuation, see Figure 3).
What surprised me was that temperatures from 20-30ºC did not result in different fermentation times; all of the fermentations reached terminal gravity at 120 hours, from 20ºC to 30ºC. The ferment at 33.5ºC reached terminal gravity (~1.030) a bit later (144 hours)
Figure 2 Panel A from https://www.biorxiv.org/content/10.1101/2021.06.15.448505v1
Maximum rate of fermentation based on rates of specific gravity decline per minute for SafAle US-05 at eight temperatures ranging from 20°C to 42°C.
Figure 2 shows the maximum fermentation rate for SafAle US-05 at different temperatures. Note that this doesn't perfectly correlate with total length of fermentation - this is just the maximum peak in fermentation speed. Figure 2 shows that the optimum temperature for US-05 is around 28°C. Above 28ºC, the max rates of fermentation decline rapidly.
The astounding result is when we compare the US-05 rates across the temperature gradient with the other kveik yeasts. (Figure 5 from https://www.biorxiv.org/content/10.1101/2021.06.15.448505v1.)
Every single kveik strain has a higher maximum fermentation rate at every tested temperature when compared to US-05. This shows that kveik yeasts are not high temperature specialists - they generally have an overall higher rate of activity at all tested temperatures.
This could have a pretty large impact on how brewers use these yeasts; using a 'neutral' kveik yeast like Lutra at any temperature will yield a faster ferment than US-05. There are significant flavour differences between Omega Lutra and US-05 across the temperature range but these may not matter depending on the beer style (i.e., beers that have a lot of hop derived flavour or roasted malts, which would both potentially overwhelm the differences in yeast derived flavours).
Figure 3 Panel A from https://www.biorxiv.org/content/10.1101/2021.06.15.448505v1
Influence of temperature on the apparent attenuation (%) of fermentations in standard wort for SafAle US-05.
US-05 attenuated our standard wort relatively well (~80%) from 20-30ºC. At 33.5ºC, the apparent attenuation started to decline (74%). Above that and the apparent attenuation was so low that there was very little fermentation and a lot of leftover residual sugars.
Figure 4 Panel A from https://www.biorxiv.org/content/10.1101/2021.06.15.448505v1
Intensity of 11 quantitative sensory descriptors of bright beer fermented by SafAle US-05 at eight temperatures ranging from 20°C to 42°C.
What about the sensory characteristics for US-05 across the temperature range? Unfortunately due to covid, it was not possible to do a large tasting panel. Instead, two tasters tasted the beers without knowledge of which temperature it was fermented at (we were blind to the variable). The figure above shows our mean rating in 11 different sensory characteristics.
First off, we decided not to rate the ferments at 37ºC or above because the fermentations weren't even close to finished and the resulting beer, if you could call it that, was extremely sweet and tasted like wort.
At 20ºC, the beer fermented with US-05 was well balanced and quite drinkable - light esters, nice malty notes, good mouthfeel and body, and very low acidity or astringency. This is the US-05 we know and love. As temperatures increased, the off-flavours rose rapidly; by 33.5ºC the beer had overwhelming solvent/fusel-alcohol flavours and lingering astringency and acidity. The beer fermented at 33.5ºC with US-05 was an awful, hot, fusel mess.
This is in large contrast to the kveik strains, which showed relatively low (or completely absent) off-flavours at temperatures up to 42ºC.
Conclusions:
Kveik have a higher temperature optimum (33.5ºC-37ºC) than modern American Ale yeast US-05 (28ºC).
American Ale yeasts like US-05 may have lost the ability to tolerate high temperatures over time through successive repitching at low temperatures
US-05 attenuates wort very poorly at 37ºC or higher.
Kveik yeasts seems to produce fewer off-flavours when fermented at high temperatures, compared to US-05
I do not recommend fermenting at 30ºC or higher when using US-05, the resulting beer is not very drinkable.
References:
Norwegian Kveik brewing yeasts are adapted to higher temperatures and produce fewer off-flavours under heat stress than commercial Saccharomyces cerevisiae American Ale yeast
Dimitri Kits, Lars Marius Garshol
bioRxiv 2021.06.15.448505; doi: https://doi.org/10.1101/2021.06.15.448505