Changes

Scientific research in Belgium and the US has shown a regular general pattern to the microbial succession of spontaneous fermentation beer. <ref name="Van Oevelen et al., 1977">[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1977.tb03825.x/abstract/ Van Oevelen et al., 1977]</ref> <ref name="Bokulic et al., 2012" /> <ref name="Spitaels et al., 2014">[http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0095384#pone-0095384-g004/ Spitaels et al., 2014]</ref> <ref name="Spitaels et al., 2015" />. This has been illustrated well by Raj Apte <ref>[http://www2.parc.com/emdl/members/apte/slides_nchf.pdf Raj Apte Concepts of sour Beer, 2004]</ref>. The first stage, which lasts for approximately 1 month <ref name="Van Oevelen et al., 1977" /> <ref name="Martens et al., 1992">[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1992.tb01126.x/abstract/ Martens et al., 1992]</ref>, is dominated by ''enterobacteria'' that produce large amounts of DMS which can be smelled during the early stages of fermentation (see [[Dimethyl Sulfide]] for more details). Examples of specific species of ''enterobacteria'' found in this early stage include ''Klebsiella aerogenes'', ''Enterobacter aerogenes'', ''Escherichia coli'', ''Citrobacter freundii'', ''Enterobacter cloacae'', and ''Hafnia alvei''. Although these ''enterobacteria'' contribute little in terms of gravity drop over the first month of fermentation, they do contribute aroma and flavor compounds and precursors during the initial stages of spontaneous fermentation, particularly acetoin, 2,3 butanediol, acetic acid, lactic acid, succinic acid, and small amounts of glycerol, ethyl acetate, and higher alcohols which might form esters in the later stages of fermentation <ref name="Martens et al., 1992" />. Acidifying the wort to pH = 4 before cooling and exposing to ambient microbes in a coolship can eliminate the ''enterobacteria'' phase of spontaneous fermentation <ref name="Spitaels et al., 2015" />. Wort or beer fermenting during this stage that includes ''enterobacteria'' should not be consumed due to potential health risks. Oxidative yeasts are also present during the first stage of fermentation, including species of ''Rhodotorula'', ''Candida'', ''Cryptococcus'', and ''Pichia'', some of which might survive pre-acidification <ref name="Bokulic et al., 2012" />.