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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).
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'' pediococci that are ropy have been found to be more acid, alcohol, and SO2 tolerant than other ''Pediococci''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" />.
One study showed that the production of β-glucan coincided with the end of the growth phase of ''Pediococcus''. While small amounts of β-glucan were produced during growth, after 2 days of growth, β-glucan production increased as growth slowed. β-glucan production stopped when growth stopped. This study showed that β-glucan production is linked to ''Pediococcous'' growth, producing more towards the end of growth. This study found that other variables were not factors in the production of β-glucan, such as differing levels of alcohol (although alcohol interacts with the β-glucan in a way that makes the viscosity seem thicker). The study also found that the lack of agitation increased the β-glucan production (wine makers will often agitate or aerate ropy wine to cure the wine from ropiness). A higher initial pH encourages higher growth (5.5+), which increases β-glucan production. A lower initial pH (3.5), decreases growth and β-glucan production. A higher concentration of glucose increased growth and β-glucan production. Glucose is needed for β-glucan production. While fructose alone is mostly insufficient to produce ropiness, a combination of glucose and fructose was slightly more efficient than glucose alone <ref name="ESP"></ref>. The introduction of malic acid, glucose, fructose, and/or nitrogen from things like fruit that is added to sour beer or even sugar added for natural carbonation can trigger ''Pediococcus'' growth and EPS production.