Changes

During both primary and secondary fermentation, a complex set of interactions occurs between the various yeast and bacteria species. Much of this is as yet unknown scientifically. For example, the production of [[Lactic Acid|lactic acid]] by lactic acid bacteria not only stresses and limits growth of ''S. cerevisiae'', but it can also turn off "glucose repression", meaning that instead of consuming simple sugars first, ''S. cerevisiae'' stops choosing which sugar types to consume first and consumes all sugar types indiscriminately. This can result in under-attenuation problems in the short run, but also more residual sugars for ''Brettanomyces'' (see [[Lactic Acid|lactic acid]] for details). Another example is that co-fermenting with brewer's yeast and ''Lactobacillus'' can create a different flavor profile than if they are staggered with a kettle souring method (see [[Lactobacillus#Effects_on_Mixed_Fermentation|effects of ''Lactobacillus'' on mixed fermentation]]). Another example is that some studies support that in nitrogen rich substrates, ''S. cerevisiae'' will synthesize simpler amino acids from the more complex nitrogen sources, and those amino acids contribute to the sustained survival of both ''Lactobacillus'' and ''Brettanomyces'' in the more stressful, post-fermentation environment <ref>[https://academic.oup.com/femsyr/article-abstract/17/4/fox018/3867021/The-influence-of-Dekkera-bruxellensis-on-the?redirectedFrom=fulltext The influence of Dekkera bruxellensis on the transcriptome of Saccharomyces cerevisiae and on the aromatic profile of synthetic wine must. Janez Kosel Neža Čadež Dorit Schuller Laura Carreto Ricardo Franco-Duarte Peter Raspor. 2017.]</ref><ref>[http://www.sciencedirect.com/science/article/pii/S2405471217303903?via%3Dihub Yeast Creates a Niche for Symbiotic Lactic Acid Bacteria through Nitrogen Overflow. Olga Ponomarova, Natalia Gabrielli, Daniel C.Sévin, Michael Mülleder, Katharina Zirngibl, Katsiaryna Bulyha, Sergej Andrejev, Eleni Kafkia, Athanasios Typas, Uwe Sauer, Markus Ralser, Kiran Raosaheb Patil. 2017.]</ref> (see also [https://www.facebook.com/groups/MilkTheFunk/permalink/1856920997669439/ this MTF thread]).

====Secondary Fermentation====

Some brewers (including homebrewers and professional brewers) do not find it necessary to move the mostly attenuated beer into a secondary vessel. Instead, the mixed culture is pitched directly into the primary fermenter. While yeast autolysis is a concern in regular brewing, it is not a cause for concern in mixed fermentations that contain ''Brettanomyces''. Lambic brewers, for example, perform a primary fermentation in barrels and leave the beer in the barrels during the beer's entire aging process, which is usually 1-3 years <ref>[http://www.lambic.info/Brewing_Lambic#Barrels Lambic.info Wiki. Brewing Lambic. Retrieved 6/8/2015.]</ref>. Yeast autolysis releases trehelose, acids, and other compounds, which are metabolized by ''Brettanomyces'' <ref>[http://www.mbaa.com/districts/michigan/events/Documents/2011_01_14BrettanomycesBrewing.pdf Brettanomyces in Brewing the horse the goat and the barnyard. Chad Yakobson. 1/14/2011.]</ref>. Maintaining a [[Solera]] may be an exception to this (see the [[Solera]] page for details). The advantage of not moving the beer into a secondary vessel is that less overall oxygen is introduced into the beer (oxygen exposure will contribute to more acetic acid and then ethyl acetate production), and might be the best option if the brewer does not have a closed/CO2 system to prevent exposure to oxygen during transferring. Some [[Brettanomyces#Nitrogen_Metabolism|evidence suggests]] that the nutrients released by yeast autolysis are beneficial to ''Brettanomyces'', so leaving the beer on the yeast cake might even be more desirable than not.

====Aging====