Changes

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. 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 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. The phenol 4-vinylguaiacol 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. They also produced the lowest amount of the ethyl phenols compared to the other ''Brettanomyces'' strains. 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 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 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 was elevated at the higher fermentation temperature versus the lower fermentation temperature) <ref name="Tyrawa_2019" />.