Changes

Their results showed that there is a vast diversity in how temperature effects attenuation for different strains of ''B. bruxellensis''. In general, the cooler 15°C (59°F) fermentation temperature slowed the attenuation rate for most strains. The US-05 attenuated the most at both temperatures, with only one saison strain matching that attenuation level when fermented at 22.5°C (72.5°F). This same strain, which was isolated from a commercial USA saison beer, and the BSI Drei strains had fast attenuation rates that were comparative to the US-05 fermentation at both temperatures, while the other strains had lag times of 8-10 days at 15°C (59°F) or 2-4 days at 22.5°C (72.5°F). Additionally, the colder temperature resulted in a wide variance between strains and their ability to ferment different types of sugars. Glucose and fructose were the only sugars fermented by all strains at the lower fermentation temperature by all of the strains, with a lot of variation for fructose, sucrose, maltose, maltotriose, cellobiose, and maltodextrin. Only BSI Drei and both of the wine strains were able to ferment cellobiose at the colder fermentation temperature (several of the saison strains began fermenting cellobiose at the warmer temperature, while others did not), indicating that colder temperatures can greatly limit or even eliminate the ability to ferment cellobiose in most strains, and maybe the environment from which the strains were isolated from determines the efficiency to ferment different types of sugars for different strains of ''B. bruxellensis'' <ref name="Tyrawa_2019" />.

At 15°C (59°F), none of the ''Brettanomyces'' strains could match the US-05 attenuation, with most of them falling to around 25-50-25% less final attenuation after 28 days, and one of the wine strains and one of the USA saison strains fermented almost nothing not fermenting at all. Still, this data showed that some beer strains of ''B. bruxellensis'' can ferment at lower temperatures. Interestingly, one of the wine strains was almost unaffected by the difference in fermentation temperature; it only lagged for a couple of days longer in the colder 15°C (59°F) fermentation temperature versus the warmer 22.5°C (72.5°F) fermentation temperature , but achieved the same amount of attenuation after 28 days <ref name="Tyrawa_2019" />.

At 22.5°C (72.5°F), all of the ''Brettanomyces'' strains fermented much bettermore efficiently, although their final attenuation numbers for some strains were significantly less than other strains and quite varied, with only one strain (the previously mentioned strain that was isolated from a commercial USA saison beer) attenuating at levels that matched the US-05 control, and three . Three strains (one wine strain and two beer strains) attenuated just over half of the rate as the more successful fermenters. This indicates that most ''B. bruxellensis'' strains are not as efficient at fermenting wort by themselves as ''Saccharomyces cerevisiae'' ale strains, and there is a a lot of diversity between ''B. bruxellensis'' strains on how efficiently they can ferment wort <ref name="Tyrawa_2019" />.

The effect on phenol production, 4-ethylguaiacol (clove) and 4-ethylphenol (barnyard), was relatively the same and above flavor threshold for both fermentation temperatures for all of the ''B. bruxellensis'' strains tested, although some strains had slightly more or less of these phenols produced at the different fermentation temperatures. The By comparison, the temperature of the fermentation had a much larger impact on the amount of esters produced. Ethyl acetate (pineapple/pear) was significantly higher in the warmer fermentation temperature of 22.5°C (72.5°F) than the cooler temperature of 15°C (59°F) for all strains, with one saison strain producing significantly more ethyl acetate and another saison strain producing significantly less ethyl acetate than the other strains. As expected, the US-05 produced higher amounts of 4-vinylguaiacol (clove) and isoamyle acetate (banana) at 22.5°C (72.5°F) and lower amounts at 15°C (59°F). The US-05 produced comparably high amounts of phenethyl alcohol (dried rose), phenethyl acetate (honey/rose pedal), and isoamyl alcohol (banana/oily) at both temperatures. These esters were generally not produced at more than very low levels by the ''Brettanomyces'' strains, except for . The phenol 4-vinylguaiacol which was produced more at the lower temperature by BSI Drei and one of the saison strains, indicating that the lower fermentation temperature slowed the process of these strains to convert the 4-VG to 4-EG, and they . They also produced the lowest amount of the ethyl phenols compared to the other ''Brettanomyces'' strains. The All of the ''Brettanomyces'' strains isolated from beer produced other fatty acid esters at significant levels above tastes threshold that the US-05 produced below tastes threshold. These esters include included ethyl caproate (pineapple/apple), ethyl caprylate (pineapple), ethyl decanoate (brandy/apple) and ethyl nonanoate (fruity/rose/waxy). In general, a higher amount of these esters were produced at the higher fermentation temperature, although there were exceptions. Several of the saison strains and the lambic strain produced higher amounts of esters than the BSI Drei control, especially when fermented at the warmer temperature, demonstrating the amount of esters produced is highly variable amount among different strains of ''B. bruxellensis'', particularly when fermented at 22.5°C (72.5°F) rather than the lower fermentation temperature of 15°C (59°F). Interestingly, the two wine strains of ''Brettanomyces bruxellensis'' did not produce above threshold levels of any of these esters at either fermentation temperature (the wine strains produced did produce the highest levels of decanoic acid, which were was elevated at the higher fermentation temperature versus the lower fermentation temperature) <ref name="Tyrawa_2019" />.