• Dimitri_Kits

Voss kveik optimum temperature (revisited)

Recently, we've been working a lot assessing the impact of fermentation temperature on the fermentation rate, attenuation, and aroma/sensory characteristics of kveik yeasts. Back on March 3rd, we did a post on the fermentation kinetics of Lalbrew Voss kveik; we tested 5 temperatures (22ºC, 30ºC, 34ºC, 37ºC, and 40ºC) with only 1 replicate for every temperature (except 37ºC, where we did two replicates). Since that post, we've done much better resolved temperature gradients with Omega Lutra kveik and Escarpment Laerdal kveik - in each case 8 temperatures with triplicates for each temperature. The replication is important, because our initial Omega Lutra data (single replicates) didn't end up being nearly as good as when we replicated it better.

So now I'm doing the same for Lalbrew Voss kveik and going back to re-do the initial temperature experiment to see if I get the same results with better replication. In this follow-up, I tested the fermentation performance, attenuation, and aroma/sensory properties of Lalbrew Voss kveik at 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. As with the Laerdal and Lutra experiments, I did 2.5 gallon batches in this case rather than 5 gallon so that I could get through the experiment faster.


**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.

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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 counteract kveik pH drop

OG ~1.052

FG ~1.012

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.

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Figure 1 Panel C from https://www.biorxiv.org/content/10.1101/2021.06.15.448505v1

Influence of temperature on the general fermentation performance of Lalbrew Voss kveik

Figure 1 shows the specific gravity of triplicate fermentations at 20-42ºC for Voss kveik. In shades of blue we have 20ºC to 30ºC, in green 33.5ºC, in yellow 37ºC, orange 40ºC, and red in 42ºC. Fermentation begins rapidly after pitching with a 6-13 gravity point decrease in the first 6 hours (largest drop at 33.5-37ºC, lowest drop at 20ºC).


Obviously, temperature does influence the fermentation properties of Voss kveik. The triplicate ferments at 33.5ºC (yellow) and 37ºC (orange) look to be the fastest; terminal gravity is reached at around 30 hours at 37ºC and 48 hours at 33.5ºC. The 20ºC ferment (dark blue) is visibly the slowest and the 42ºC ferment (red) is slower than even the 28ºC ferment. It is pretty clear from this qualitative first look that Voss kveik is inhibited at 40ºC or above.


Figure 2 Panel C 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 Lalbrew Voss kveik at eight temperatures ranging from 20°C to 42°C.

Figure 2 shows the maximum fermentation rate for Voss kveik at different fermentation 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 Voss kveik is 37°C. This is comforting, because our first poorly replicated data also pointed to a thermal optimum around 37ºC and temperature-dependent inhibition/stress at temperatures at or above 40ºC.


Figure 3 Panel C 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 Lalbrew Voss kveik.

I observed no change in apparent attenuation along the entire temperature gradient - it was ~77% from 20ºC to 42ºC. This is quite surprising, because both Lutra kveik and Laerdal kveik show decreased attenuation (likely from temperature stress) at 40-42ºC.


Figure 4 Panel C from https://www.biorxiv.org/content/10.1101/2021.06.15.448505v1

Intensity of 11 quantitative sensory descriptors of bright beer fermented by Lalbrew Voss kveik at eight temperatures ranging from 20°C to 42°C.

What about the sensory characteristics 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.


Keep in mind that this is our unique perception of the sensory properties and that you, or a large panel, may find significantly different results.


At 20ºC, the beers had a noticeable 'kveiky twang' and as well as slight acidity and slight astringency. This was despite the high mash pH to offset the kveik pH drop. The malt character came through in a nice way but the body and mouthfeel were rather low. We noticed that as the temperatures increased, the fruity 'citrus, bitter/candied-orange peel' flavours really popped in a beautiful way. The highest intensity for these esters seemed to be at 40ºC. Interestingly, the acidity and astringency didn't increase much with temperature; this could be due to the very high of fruity esters masking these qualities.


My personal favourite was definitely the one fermented at 40ºC.


Conclusions:

  1. Optimal fermentation performance (max fermentation rate) for Voss kveik is at 37ºC, like our previous analysis showed.

  2. Temperatures 40ºC or higher inhibited fermentation, although the performance was still robust (full attenuation and 'fast' fermentation).

  3. Fruity esters seemed to peak at 40ºC and this temperature produced (to us) the most enjoyable and drinkable beer.

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







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