13,701
edits
Changes
→"Ropy" or "Sick" Beer
[[File:EPS.gif|thumb|300|Exopolysaccharide pathway <ref name="ESP">[http://www.sciencedirect.com/science/article/pii/S0740002004000668 Glucose fermentation kinetics and exopolysaccharide production by ropy Pediococcus damnosus IOEB8801. Emilie Walling, Marguerite Dols-Lafargue, Aline Lonvaud-Funel. Food Microbiology Volume 22, Issue 1, January 2005, Pages 71–78.]</ref>]]
Some strains of ''P. damnosus'' (and other bacteria) can cause a beer (or wine) to go "ropy", also known as "sick" by [[lambic]] brewers (or more specifically as "the fat sickness"; “la maladie de la graisse” in French <ref>[https://beerbybart.com/2011/04/03/true-lambic-jean-van-roy-cantillon-sick-beer/ True Lambic: Sick beers and the magic of Cantillon. Beer By Bart blog. Gail Ann Williams. 04/03/2011. Retrieved 04/23/2016.]</ref>). Reportedly, ropiness in beer that also has ''Brettanomyces'' (which is traditionally credited with breaking down the ropiness after a period of rest) usually lasts anywhere from 1 week to 3 months, although fewer reports claim that it has lasted as long as 7 months (see reference for different experiences of brewers) <ref name="ropy_time">[https://www.facebook.com/groups/MilkTheFunk/permalink/1132030550158491/ Poll on Milk The Funk regarding how long ropy beer has been observed. 08/20/2015.]</ref>. Some species of ''Pediococcus'' and other lactic acid bacteria have been reported to also be able to break down ropiness <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1670311836330357/?comment_id=1670331339661740&comment_tracking=%7B%22tn%22%3A%22R0%22%7D Matt Humbard and Joe Idoni. Milk The Funk Facebook group. 04/29/2017.]</ref>. Despite the popularity of this talking point about ''Pediococcus'' in brewing, a lot of strains of ''Pediococcus'' used in brewing don't seem to produce ropiness, especially strains sourced from beer yeast labs. For example, Richard Preiss of [[Escarpment Laboratories]] reported only seeing ropiness from ''Pediococcus'' sourced from [[lambic]] <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2859721020722760/?comment_id=2859868767374652&comment_tracking=%7B%22tn%22%3A%22R%22%7D Richard Preiss. Milk The Funk Facebook group thread on the frequency of ''Pediococcus'' caused ropiness. 08/20/2019.]</ref>. The exact enzymatic activity for how ''Brettanomyces'' (or other microorganisms) break down EPS from ''Pediococcus'' is not well characterized, but it could be due to alpha-glucosidase activity in those yeasts (see [[Pediococcus#Carbohydrate_Metabolism|Carbohydrate Metabolism]] above).
[https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-37-0034 Oevelen and Verachtert (1979)] demonstrated that ''Brettanommyces bruxllensis'' reduces the viscosity of ropiness produced by ''Pediococcus'' , but that at least one strain of ''Saccharomyces cerevisiae'' does not <ref name="Oevelen_1979" />. The scientists tested two strains of ''B. bruxellensis'', and when either one of these strains were co-pitched with a strain of ''P. damnosus'' (formerly called ''P. cerevisiae''), at two weeks there was the same level of viscosity as when the ''P. damnosus'' strain was pitched by itself, but at 4 weeks the viscosity was greatly reduced (although the viscosity was still higher than when there was no ''Pediococcus'' present). When they co-pitched a strain of ''Saccharomyces cerevisiae'' with the ''Pediococcus'', the viscosity remained high at 4 weeks, demonstrating that this strain of ''S. cerervisiae'' was not able to reduce the viscosity of the ropiness (it is not known if this strain of ''S. cerevisiae'' was diastatic or not). The scientists also attempted to stagger the pitch of ''Brettanomyces'', pitching it two weeks after the ''Pediococcus''. This resulted in very low growth of the ''Brettanomyces'' and no reduction in viscosity due to that limited growth. The limited growth was attributed to the low pH that the ''Brettanomyces'' yeast was exposed to at inoculation time. The ''Brettanomyces'' was able to reduce the viscosity when the scientists add another 10 g/L of glucose, and buffered the pH to 4 <ref name="Oevelen_1979" />. The exact enzymatic activity for how ''Brettanomyces'' (or other microorganisms) break down EPS from ''Pediococcus'' is not well characterized, but it could be due to alpha-glucosidase activity in those yeasts (see [[Pediococcus#Carbohydrate_Metabolism|Carbohydrate Metabolism]] above).
This "ropiness" is caused by production of exopolysaccharides (EPS) in the form of β-glucans (beta glucans) by some strains ''Pediococcus'' and some other lactic acid bacteria species. The β-glucans are made up of beta 1, 3 linkages and beta 1, 2 branches composed of single units <ref name="Wade_2018" />. A small amount (20-30 mg/L <ref name="Wade_2018" />) of β-glucan is adequate enough to affect the visible viscosity of beer or wine. The gene known as "dps" has been identified with the production of β-glucan/EPS in ''P. damnosus'', and the gene "gtf" in ''P. claussenii'' <ref name="Snauwaert"></ref>. Not all strains of ''P. damnosus'' express the gene, and only ones that do will cause a beer to go ropy. Although it is not needed to survive in beer, EPS production is probably has importance in biofilm production <ref>[http://cat.inist.fr/?aModele=afficheN&cpsidt=23890699 Ethanol tolerance of lactic acid bacteria, including relevance of the exopolysaccharide gene gtf. Pittet V, Morrow K, Ziola B. 2011.]</ref>, and pediococci that are ropy have been found to be more acid, alcohol, and SO2 tolerant than other pediococci. The thickness of the ropiness is increased with the presence of malic acid <ref name="ESP"></ref>. While strains of ''P. damnosus'' and ''P. parvulus'' are the ''Pediococcus'' species most associated with ropiness, some strains of ''P. pentosaceus'' have also been found to produce EPS <ref name="Wade_2018" />.