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edits
Changes
→Fourth Stage: Maturation
This phase generally begins somewhere around month four to eight, with these microbes completely dominating at around 9-13 months <ref name="Roos_2018_2" /><ref name="curtain_asbc_2018" />(~26 minutes in). Additional attenuation occurs very slowly for another 7-18 months. De Roos et al. (2018) reported a gradual drop from 4 Plato to 0.5 °Plato during the maturation phase. <ref name="Roos_2018_2" />. During this extended maturation phase, ''Brettanomyces'' continues to ferment the residual sugars leftover in the beer using intra- and extracellular alpha-glucosidase, and produces most of the final aromatic and flavor compounds in the form of esters, phenols, and fatty acids found in finished Belgian lambic and other spontaneously fermented beers (see [[Brettanomyces#Brettanomyces_Metabolism|''Brettanomyces'' metabolism]]). During the maturation phase, a [[pellicle]] is formed from the ''Brettanomyces'', as well as oxidative yeasts from the genera ''Pichia'', ''Candida'', ''Cryptococcus'', and ''Torulspsis'' <ref name="Van Oevelen et al., 1977" /><ref name="Roos_2018" /><ref name="Roos_2018_2" /><ref name="Bongaerts_2021" />. It is thought that the pellicle and the presence of these oxidative yeasts might reduce oxygen influx, and thus assist in inhibiting the growth of acetic acid bacteria <ref>[https://pdfs.semanticscholar.org/8c12/9985b9f1264179fe2e2f779bae1ff3e51a54.pdf Jacques De Keersmaecker. "The Mystery of Lambic Beer". Scientific American, Inc. 1996.]</ref>, however, this has not been proven in a scientific manner that we know of.
A study of spontaneously fermented ales at a brewery in Oamaru, New Zealand, found a greater diversity of dominate organisms at the point of beer maturation. The diversity of microbe species deviated slightly significantly from Belgian lambic beers in general , as well as the diversity between vintages sampled from barrels and between barrels for the same vintage (vintages 2016-2022 CE). The 2016 vintage was completely dominated by ''Pediococcus'' (97.6%); other genera detected included ''Lactobacillus'' (1.24%), ''Komagataeibacter'' (0.18) and Bacillus (0.13%). However, in the 2017 vintage, ''Pediococcus'' was not as predominant, as seen in the 2016 vintage. Here, ''Pediococcus'' made up 33.9%. ''Komagataeibacter'' (22.7%), ''Acetobacter'' (21.7%), and ''Paenibacillus'' (16.3%) were the other common genera associated with this vintage. The 2019 vintage was similar to the 2016 vintage where ''Pediococcus'' showed high relative abundance at 97.5%; however, ''Rhodococcus'' (0.08%) and ''Acetobacter'' (0.33%), which were not detected in previous vintages, were present here in low relative abundance. The 2021 and 2022 vintages were again dominated by ''Pediococcus'', ''Klebsiella'' and members of the Enterobacteriaceae family. The study reported some deviation between barrels sampled for the same vintage year, but also some consistency. For example, all 4 barrels of the 2020 vintage sampled had a much broader diversity of bacteria than all of the other vintages, and this was consistent between the 4 barrels sampled. The dominant fungal microbes were much more varied in this study. The 2016 vintage had a large proportion of ''Penicillium'' (74.8%). Others detected includes include ''Saccharomyces'' (4.67%), ''Aspergillus'' (4.55%), ''Hanseniaspora'' (4.33%) and ''Brettanomyces'' (4.5%). ''Cladosporium'', ''Rhodotorula'' and ''Torulaspora'' were found in small amounts (all making up less than 2%). The most abundant fungi in the 2017 vintage were ''Brettanomyces'' (31%). This was followed by ''Aspergillus'' (17.1%), ''Saccharomyces'' (12.8%), ''Debaryomyces'' (11.4%) and ''Penicillium'' (10.7%). Genera unique to this vintage include ''Naganishia'' (1.7%) and ''Pichia'' (0.16%). ''Aspergillus'', the filamentous fungi, was seen to be dominant (44%) in the 2019 vintage. ''Saccharomyces'' (26.9%), ''Penicillium'' (9.34%), ''Hanseniaspora'' (8.8%) ''Brettanomyces'' (5.4%) and ''Cladosporium'' (1.9%) were also reported. There was also a wide variation between barrels sampled for the same vintage . While the climate and proximity to the Pacific ocean of Oamaru, New Zealand might have had some impact on the deviation of microbe populations at this brewery versus Belgian lambic breweries, the authors of the study hypothesized that the much longer history of Belgian lambic breweries where microbes have had a much longer time to adapt and become well established versus the relative youth of the brewery in New Zealand (founded in 2014) might be the cause of this deviation <ref name="Ohwofasa_2025">[https://www.mdpi.com/2076-2607/13/2/224 Ohwofasa, A.; Dhami, M.; Winefield, C.; On, S.L.W. Analysis of Bacterial and Fungal Communities and Organic Acid Content in New Zealand Lambic-Style Beers: A Climatic and Global Perspective. Microorganisms 2025, 13, 224. https://doi.org/10.3390/microorganisms13020224.]</ref>.
During the extended maturation phase, a beer may become "sick" or "ropey", though not all producers get this <ref name="Spontaneous Sour Hour" /> (~1:10 min in) <ref name="Vinnie sour beer talk">[http://www.thebrewingnetwork.com/post1863/ Recording of Vinnie's talk at NHC]</ref> (~1:44 in) <ref name="Vinnie on the Session Jan 2010"/> (~3:44 in). This is the result of exopolysaccharides, which some ''Pediococcus'' strains are known to produce. These exopolysaccharides can be broken down by other microbes present in the beer relieving the beer of its "sickness" (this exopolysaccharide breakdown is generally attributed to ''Brettanomyces''). Beer may also become "sick" in the bottle during bottle conditioning. This is likely due to enhanced ''Pediococcus'' activity from additional fermentable sugar, in the form of simple sugars or beer which has not completely attenuated yet <ref name="Vinnie sour beer talk">[http://www.thebrewingnetwork.com/post1863/ Recording of Vinnie's talk at NHC]</ref> (~1:47 in). A beer that is sick in the bottle will generally clear through the same process as a younger aging beer when given appropriate time. See the [[Pediococcus#.22Ropy.22_or_.22Sick.22_Beer|Pediococcus]] page for more information.