13,589
edits
Changes
no edit summary
===Impact of Fermentation Temperature===
[[File:Tyrawa attenuation 2019.JPG|thumb|360px|[https://onlinelibrary.wiley.com/doi/full/10.1002/jib.565 '''A)''' Fermentation at 15°C (59°F) and '''B)''' at 22.5°C (72.5°F) by different strains of ''B. bruxellensis'' and Fermentis US-05; the "PEST" strains are wine strains while the others are beer strains. Source: The temperature dependent functionality of ''Brettanomyces bruxellensis'' strains in wort fermentations, by Tyrawa et al (2019).] <p>Click [https://www.facebook.com/groups/MilkTheFunk/permalink/1285391951489016/ here] for more charts and graphs from this study.</p>]]
In ''Saccharomyces'' species, higher fermentation temperature has been associated with faster fermentation, higher growth rates, and ester formation. [https://onlinelibrary.wiley.com/doi/full/10.1002/jib.565 Tyrawa et al. (2019)] set out to explore the impact of fermentation temperature on 7 beer strains (including BSI Drei and several isolates from commercial sour/saison/lambic beers) and 2 wine strains of ''B. bruxellensis''. Fermentis US-05 and the BSI Drei were used as controls. Each strain was fermented in autoclaved 100% 2-row malt wort at a starting gravity of 1.050 and fermented at 15°C (59°F) versus 22.5°C (72.5°F) for 28 days. The pitching rate was 1.2 x 10<sup>7</sup> cells/mL. Each strain was genetically tested to ensure their species was correctly identified and that they were genetically distinct from each other <ref name="Tyrawa_2019">[https://onlinelibrary.wiley.com/doi/full/10.1002/jib.565 The temperature dependent functionality of Brettanomyces bruxellensis strains in wort fermentations. Caroline Tyrawa, Richard Preiss, Meagan Armstrong, George van der Merwe. 2019. DOI: https://doi.org/10.1002/jib.565.]</ref>. The fermentation temperature of 30°C (86°F) was also briefly examined, but they were described as "smelling terrible" by Richard Preiss, and so were discarded from the study <ref name="Tyrawa_2017">[https://www.facebook.com/groups/MilkTheFunk/permalink/1285391951489016/ "Funky can be Great: Brettanomyces bruxellensis Beer Fermentations" (poster for study). Caroline Tyrawa, Richard Preiss, and George van der Merwe. 2017.] </ref>.
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 to ferment different types of sugars, with glucose . Glucose and fructose being were the only sugars fermented by all strains and at the lower fermentation temperature by all of the strains, with a lot more of variation for fructose, sucrose, maltose, maltotriose, cellobiose, and maltodextrin. At the warmer temperature, only Only BSI Drei and both of the wine strains were able to ferment cellobioseat the colder fermentation temperature (several of the saison strains began fermenting cellobiose at the warmer temperature), 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 adapted in were isolated from determines what the efficiency to ferment different types of sugars for different strains of ''B. bruxellensis'' can ferment <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 50-25% less final attenuation after 28 days, and one of the wine strains and one of the USA saison strains fermented almost nothing 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 <ref name="Tyrawa_2019" />.
At 22.5°C (72.5°F), all of the ''Brettanomyces'' strains fermented much better, 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 strains (one wine strain and two beer strains) attenuated just over half 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 strains on how efficiently they 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 temperature of the fermentation had a 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 were generally not produced at more than low levels by the ''Brettanomyces'' strains, except for 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 also produced the lowest amount of the ethyl phenols compared to the other ''Brettanomyces'' strains. The ''Brettanomyces'' strains produced other fatty acid esters at significant levels above tastes threshold that the US-05 produced below tastes threshold. These esters include 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 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 the highest levels of decanoic acid, which were elevated at the higher fermentation temperature) <ref name="Tyrawa_2019" />.
* [https://www.facebook.com/groups/MilkTheFunk/permalink/1285391951489016/ Richard Preiss summarizes his study and provides the original poster with charts and graphs of the data on Milk The Funk.]
* [https://www.facebook.com/groups/MilkTheFunk/permalink/2710564272305103/ More Q&A with Richard Preiss on Milk The Funk regarding the full published paper.]
* [[100%25_Brettanomyces_Fermentation#Are_100.25_Brett_Beers_Really_Cleaner.3F|Are 100% Brett Beers Really Cleaner?.]]
===Aging===