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→Temperature and Aromatic and Sensory Compounds
====Temperature and Aromatic and Sensory Compounds====
Just as with other strains of ''Saccharomyces cerevisiae'' used in fermentation, the fermentation temperature can have a significant effect on the different aromatic and flavor compounds produced by kveik . [https://nmbu.brage.unit.no/nmbu-xmlui/handle/11250/2681970?show=full Aasen's Master's thesis] looked at fermenting three different full culture kveiks, Gamlegrua, Gausemel and Ørjasæter, and US-05 as a control. She tested three different fermentation temperatures, 22°C, 30°C, and 37°C. In general, after 7 days of incubation time, all of the yeasts had higher levels of the esters ethyl acetate, isoamyl acetate,and ethyl hexanoate at the 22°C or 30°C, and nearly half the amounts of esters at 37°C. These were esters were also measured at day 2, and at that time they were much higher in the 37°C fermentation, suggesting that prolonged exposure to the warmer temperature may have dissipated these esters. Ethyl octanoate tended to have slightly higher amounts at 22°C or 30°C, but the differences between the different fermentation temperatures were smaller, and in the case of the Gausemel kveik there was no significant different at all for this ester <ref name="Aasen" />.
It has been anecdotally reported by brewers that high levels of off-flavors from higher alcohols are not produced at fermentation temperatures up to 35-40°C with kveik. In general, Aasen's Master's thesis reflected these anecdotal reports. The amount of the higher alcohol 2-methyl-1-propanol was nearly double at 30°C and 37°C versus 22°C for the control yeast strain, US-05. For the three kveik cultures that were tested, Gamlegrua, Gausemel, and Ørjasæter, the amount of this higher alcohol was only slightly elevated at the higher fermentation temperatures, but still remained under the lowest levels that US-05 produced when fermented at 22°C. The higher alcohol 1-propanol had a similar trend. At 30°C and 37°C, US-05 produced significantly more of this higher alcohol, while the three kveik cultures produced only slightly elevated or the same levels regardless of fermentation temperature. The levels of 1-propanol that were produced by the three kveik cultures at all three fermentation temperatures were, in general, around the same amount that US-05 produced at 22°C. Two other higher alcohols that were measured, 2-methyl-1-butanol and 3-methyl-1-butanol, were roughly the same for all three fermentation temperatures for all three of the kveik cultures and US-05, with 2-methyl-1-butanol tending to be slightly higher in the warmer fermentation temperatures for all of the kveik cultures and US-05. One of the higher alcohols tested, 2-hexanol, had nearly double or triple the levels when fermented at the cooler temperature of 22°C versus 30°C and 37°C, indicating that this particular higher alcohol follows an opposite trend than most higher alcohols produced by yeast. The levels were the same for all three of the kveik cultures and US-05 <ref name="Aasen" />.
For the kveik cultures Gamlegrua and Gausemel, Aasen reported elevated levels of acetaldehyde were found at the warmer fermentation temperatures of 37°C, but not for Ørjasæter or US-05. The aldehyde 2-methyl-propanal was elevated at
37°C for all four of the cultures tested (Gamlegrua, Gausemel, Ørjasæter , and US-05). The aldehydes 2-methyl-butanal and 3-methyl-butanal, and the ketone diacetyl, were not significant for any of the cultures tested nor at any of the different fermentation temperatures (22°C, 30°C, 37°C) <ref name="Aasen" />.
[https://www.biorxiv.org/content/10.1101/2021.07.26.453768v1 Foster et al. (2021)] found similar findings in 5 out of 6 strains of kveik (two Hornindal strains, one Laerdal strain, one Ebbegarden strain, one Granvin strain, and one Sigmund Voss strain). Using HS-SPME-GC-MS and PCA biplot analyses to measure and plot fatty acids, ethyl esters, alcohols, and acetate esters, the researchers found that, with the exception of the Ebbegarden strain, the kveik strains grouped together while the control strains (Cal ale, Vermont, and Kolsch) grouped together. For example, octanoic acid, ethyl hexanoate (pineapple, tropical), ethyl octanoate (tropical, apple, cognac), and ethyl decanoate (apple) were all produced above threshold for all (except Ebbegarden) of the kveik strains and one control strain, the Belgian strain "St. Lucifer" from Escarpment Labs, but not the Cal ale, Vermont, and Kolsch control strains. This demonstrates that the flavor profile of many but not all kveik strains is unique from at least some typical brewing strains. The flavor profile plotting also determined that temperature played a roll in flavor with all but the Ebbegarden kveik strains clustering together at 5-42°C versus 15-22°C. For example, ethyl octanoate and ethyl decanoate were produced at the higher temperature range in the kveik strains (except Ebbegarden). The higher alcohol 1-octanol, which has a pleasant citrus character, was only produced above threshold by Cal ale and Kolsch at 15°C and Vermont at 22°C, it was produced above threshold by the kveiks and St. Lucifer strains at a much wider temperature range. Similar results were found for isoamyl acetate. Phenethyl acetate, on the other hand, was only produced above threshold by Hornindal1, Hornindal2, Laerdal and St. Lucifer regardless of temperature
<ref name="Foster_2021" />.
====Other Sensory Data====