13,591
edits
Changes
added Pedio ropy timeframe based on MTF poll
==="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'' can cause a beer (or wine) to go "ropy". 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>[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>. This "ropiness" is actually caused by production of exopolysaccharides (EPS) in the form of β-glucans (beta glucans). A small amount 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. Not all strains of ''P. damnosus'' express the gene, and only ones that do will cause a beer to go ropy. ''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>.
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 would explain why beer containing ''Pedio'' often goes ropy shortly after naturally carbonating in the bottle. This study found that other variables were not factors in the production of β-glucan, such 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. A low starting pH decreases growth, and therefore decreases β-glucan production. Glocuse is needed for β-glucan production. While fructose alone is mostly insufficient, a combination of glucose and fructose was slightly more efficient than glucose alone <ref name="ESP"></ref>.