Omega Lutra kveik optimum temperature and performance review

This is another addition to our series on fermentation performance and temperature optima of various kveik yeasts. In previous posts, we've shown kveik yeast are heterogeneous in their response to elevated temperatures (>30ºC), we've uncovered the optimum fermentation temperature for various kveik (Voss, Laerdal), and reviewed other kveik (Krispy).

This next post is about Lutra kveik and its optimum fermentation temperature. Some of you may remember my post from Feb 1, where I did ferments using Lalbrew Voss, Omega Hornindal, and Omega Lutra at 'typical ale temperatures' (22ºC) and 'hot temperatures (>35ºC). For Lutra, the maximum fermentation rate was higher at 22ºC than at 35ºC. The 35ºC ferment with Lutra did finish faster than the 22ºC - 71 hours vs 88 hours - but this difference seemed small at the time. At the time, I boasted that Lutra kveik seems to prefer lower temperatures and that stress seemed apparent at 35ºC.

This data was based off 3 ferments, 1 replicate at 22-24ºC and 2 replicates at 35ºC. With my latest work on Escarpment Laerdal kveik, I actually managed to test 8 temperatures (20ºC, 25ºC, 28ºC, 30ºC, 33.5ºC, 37ºC, 40ºC, and 42ºC) with triplicate ferments. I wanted to revisit the Lutra kveik data to see if my first assessment of its temperature preference was correct or not.

In this experiment I used the same exact recipe and process that I used for all of my previous kveik 'test' ferments. As with the Escarpment Laerdal kveik post, 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 are also available in updated form 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 1.049

FG 1.012-1.025 (attenuation varied by temperature)

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 pack per 5 gallons (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: Fermentation kinetics for Lutra kveik fermented in triplicate at 8 different temperatures (20ºC-42ºC)

Figure 1 shows the specific gravity of triplicate fermentations at 20-42ºC for Lutra kveik. In shades of blue we have 20ºC to 30ºC, in green 33.5ºC, in yellow 37ºC, orange 40ºC, and red being 42ºC. Fermentation begins rapidly after pitching with a 3-7 gravity point decrease in the first 3 hours (7 gravity points at 33.5ºC, 3 points at 20ºC).

What is immediately apparent is that temperature does influence fermentation rate and finishing time for Lutra kveik. Below you can find how long it took for each triplicate fermentation to finish at each temperature:

20ºC: 100 h

25ºC: 74 h

28ºC: 59 h

30ºC: 48 h

33.5ºC: 48 h

37ºC: 74 h

40ºC: 30 h**

42ºC: 74 h

20ºC is the slowest by far, taking 100 hours to reach terminal gravity. **You might be tempted to conclude that 40ºC is the best temperature, but that's likely not the case and I'll explain later why. The longest fermentation times are at 'cool' temperatures (20ºC) and decrease as the temperature increases (i.e. things get faster), with a trough at 30-33.5ºC where performance is likely optimal, until 37ºC where we see that fermentation times increase again. Basically, it looks like temperature-dependent inhibition (i.e. stress) begins somewhere above 33.5ºC because we already see inhibition at 37ºC.

Figure 2: Effect of temperature on maximum fermentation activity in triplicate at 8 different temperatures (20ºC-42ºC) for Lutra kveik

Figure 2 shows the maximum fermentation rate for Lutra 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 clearly that the optimum temperature is likely around 33-34ºC for Lutra kveik. The fermentation rates start to drop by 37ºC.

Figure 3: Effect of temperature on apparent attenuation in triplicate at 8 different temperatures (20ºC-42ºC) for Lutra kveik

I did observe a trend of decreasing apparent attenuation at higher temperatures (though not nearly as pronounced as for Laerdal kveik). Apparent attenuation was 79% from 28ºC to 37ºC. Above 37ºC, there was a decrease in the apparent attenuation to 75%. This is likely caused by the heat stress at 40ºC-42ºC. This matches the results in Figure 2; temperatures much greater than the optimum temperature lead to stress and reduced attenuation.

Figure 3 also explains why 40ºC is not the best fermentation temperature. The fermentation finished slightly faster than at the optimum temperature (33.5ºC, 48h), but at the cost of nearly 5% in attenuation.

Figure 4: Impact of fermentation temperature on sensory properties of Lutra kveik (rating out of 5)

But how do the beers actually taste? 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 temperatures around 20ºC, the beers made with Lutra kveik had a very slight fruity ester character, good body and mouthfeel that accentuated the malt character nicely, and were highly drinkable. Very surprisingly, we didn't detect much more 'fruity' esters at higher temperatures; rather, we both picked up increasing astringency and acidity (the kveiky 'twang') even though we adjusted the mash pH to 5.5 for all of the fermentations. The sweet spot for me, in taste and performance, is at 28ºC - you still get really neutral and soft flavours but very quick turnaround time.

So was I right in the Feb 1 post, where I stated that Lutra kveik prefers 'cool' temperatures (22ºC-24ºC) over 35ºC? With a much better design and far more replication, I can say that I was not correct!! This is a big lesson learned for me; I made a strong conclusion based on only testing 2 temperatures with only 1 or 2 replicates. It really takes doing a careful temperature gradient and good replication to get reliable results.

If you look at Figure 2, the fermentation rate at 25ºC and 37ºC are both far from the optimum (I know that I tested 22ºC-24ºC in the Feb 1 study but 25ºC is not far off). So it looks like I tested significantly below the temperature optimum and then slightly above it - this was NOT enough to estimate the optimum temperature.

Conclusions:

1) Optimal fermentation performance for Lutra kveik (Omega Yeast) is around 33-34ºC. It could be slightly higher like 35ºC, but I didn't test 35ºC exactly.

2) Temperatures of 37ºC or higher inhibited fermentation.

3) Lutra still ferments and attenuates relatively robustly at 40ºC and 42ºC (unlike Laerdal kveik, which is severely restricted at 40-42ºC).

4) Lutra kveik seemed (to us) to produce beers with more acidity and astringency than we liked at 40ºC-42ºC. I think a good balance between speed and flavour is 28ºC.

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I've got to give a huge shout out to Dr. Laura Burns from Omega Yeast. She reached out to me over facebook and communicated, very graciously and openly, that their internal research showed robust performance for Lutra kveik at 'high' temperatures and that my first post was somewhat inconsistent with their data. She was incredibly open, nice, and considerate when she had the right to be highly critical of my previous post. And I have to say that Laura and the staff at Omega Yeast are right; Lutra kveik performs robustly at temperatures even as high as 42ºC (if you're OK seeing some loss in apparent attenuation). The optimal temperature is somewhere in the 33-35ºC range, but brewers can feel comfortable going much higher than this.