Changes

The same study by Martens et al. looked at two casks during the third fermentation, where the "heavy beer" beer was transferred from the secondary fermentation vessel to age for two years. At the beginning of the third phase of fermentation, ''Saccharomyces'' cell counts began to drop while the appearance of ''Brettanomyces'' began. After 10 weeks in the casks, ''Lactobacilli'' greatly decreased, giving rise to strains of ''Pediococcus parvulus''. After 12 weeks for Cask A and 18 weeks for Cask B, the beer no longer contained ''Saccharomyces'', and ''Brettanomyces'' dominated. Specifically, ''B. lambicus'' (now classified as a strain of ''B. bruxellensis''<ref name="snauwaert"></ref>) and ''B. bruxellensis'' were the dominate species, but much smaller counts of ''B. intermedius'' (now classified as ''B. anomala'') and ''B. custersianus'' were also found. The ''Brettanomyces'' species continued to be the primary microorganisms for 36 weeks in Cask A and 50 weeks in Cask B. After this time period, ''P. parvulus'' began to dominate. Acetic acid bacteria also began to make an appearance in the casks, being detected at 27 weeks in Cask A and 40 weeks in Cask B. The exact numbers of the acetic acid bacteria were not reported by this study since they mostly grow on the surface of the beer inside the cask, and possibly on the walls of the cask where diffused oxygen could reach them more easily, and samples were not taken from these sections of the casks. The difference in the time periods for the microbial populations was determined to be affected by the casks themselves, which differed in age, size, and possibly different microbe colonization inside them before they were filled <ref name="Martens"></ref>. During the third fermentation phase, lactic acid greatly increases from ~600 ppm to ~4500 ppm after 35 weeks, and then slowly increases to ~5200 ppm at 60 weeks, at which time L-lactic is only slightly less (~48%) than D-lactic acid <ref name="Verachtert"></ref>. Acetic acid levels reached 1600 ppm by the end of the third phase. The final pH of the "heavy beer" is around 3.2-3.5 <ref name="snauwaert"></ref>.