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'''Pediococcus''' (often referred to by brewers as "Pedio") are Gram-positive lactic acid bacteria (LAB) used in the production of Belgian style beers where additional acidity is desirable. They are native to plant material and fruits <ref name="ucdavis">[http://wineserver.ucdavis.edu/industry/enology/winemicro/winebacteria/pediococcus_damnosus.html Viticulture & Enology. UC Davis website. Pedioccous damnosus. Retreived 07/28/2015.]</ref>, and often found in spontaneously fermented beer as the primary source of lactic acid production (with ''P. damnosus'' being the only species identified in lambic) <ref>[http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0095384 The Microbial Diversity of Traditional Spontaneously Fermented Lambic Beer. Freek Spitaels, Anneleen D. Wieme, Maarten Janssens, Maarten Aerts, Heide-Marie Daniel, Anita Van Landschoot, Luc De Vuyst, Peter Vandamme. April 18, 2014.]</ref><ref>[[Scientific_Publications#Lambic_and_Spontaneous_Fermentation|Multiple Scientific publications linked on MTF.]]</ref>. The ability to grow in beer is strain dependent rather than species dependent, however genetic differences indicate that ''P. damnosus'' and ''P. claussenii'' are better adapted to surviving in beer than ''P. pentosaceus'' <ref name="Snauwaert">[http://www.biomedcentral.com/content/pdf/s12864-015-1438-z.pdf Comparative genome analysis of Pediococcus damnosus LMG 28219, a strain well-adapted to the beer environment. Isabel Snauwaert, Pieter Stragier, Luc De Vuyst and Peter Vandamme. 2015.]</ref>. Like many bacteria, Pediococci have the ability to [https://en.wikipedia.org/wiki/Horizontal_gene_transfer transfer genes horizontally] without reproduction <ref name="Snauwaert"></ref>. They are generally considered to be facultative anaerobes, which means they grow anaerobically but can also grow in the presence of oxygen <ref>[http://textbookofbacteriology.net/lactics.html Lactic Acid Bacteria. Todar's Online Texbook of Bacteriology. Kenneth Todar, PhD. Pg 1. Retrieved 08/09/2015.]</ref>. Some species/strains (including individual strains of ''P. damnosus'') can have their growth and acid production inhibited by oxygen <ref name="NAKAGAWA">[https://www.jstage.jst.go.jp/article/jgam1955/5/3/5_3_95/_article TAXONOMIC STUDIES ON THE GENUS PEDIOCOCCUS. ATSUSHI NAKAGAWA, KAKUO KITAHARA. 1959.]</ref>, while some will have better growth and produce more acid in the presence of oxygen (microaerophilic) <ref>[http://www.ncbi.nlm.nih.gov/pmc/articles/PMC357257/ THE NUTRITION AND PHYSIOLOGY OF THE GENUS PEDIOCOCCUS. Erling M. Jensen and Harry W. Seeley. 1954.]</ref><ref>[http://www.microbialcellfactories.com/content/8/1/3#B5 Pediocins: The bacteriocins of Pediococci. Sources, production, properties and applications. Maria Papagianni and Sofia Anastasiadou. 2009.]</ref>. Strains found in beer are hop tolerant <ref>[http://www.biomedcentral.com/1471-2164/16/267 Comparative genome analysis of Pediococcus damnosus LMG 28219, a strain well-adapted to the beer environment. Isabel Snauwaert, Pieter Stragier, Luc De Vuyst and Peter Vandamme. April 2015.]</ref>. Due to their continued metabolism of longer chain polysaccharides, acid production will increase with storage time. ''Pediococcus'' can form a [[pellicle]].
''Pediococcus'' may also cause “ropiness” (also called a "sick beer") due to the production of exopolysaccharides. "Ropy" or "sick" beer is more viscous and, in extreme circumstances, can form strands. Sickness effects mostly the mouthfeel and appearance of beer, and may have no influence on the flavor. It is considered a temporary flaw in sour beer. Some brewers, including Vinnie Cilurzo from Russian River Brewing and some Belgian lambic producers, claim that after the ropiness goes away (generally in 3-6 months <ref name="ropy_time"></ref>) it produces a deeper acidity and mouthfeel, and is viewed as a positive process in the production of sour beer <ref>[http://www.xxlbrewing.com/hb/sour_beer/img_09.html 2007 AHA Sour Beer presentation by Vinnie Cilurzo.</ref>. For other brewers, ropy beer is seen as a nuisance due to the beer needing to be aged for a longer period of time. ''Pediococcus'' species can also produce diacetyl with extended storage time<ref name="Garcia-Garcia" />. [[Brettanomyces]] can break down exopolysaccharides and diacetyl produced by ''Pediococcus'' and the two are often used together.
See [[Lactobacillus]], [[Brettanomyces]], [[Saccharomyces]], and [[Mixed Cultures]] charts for other commercially available cultures.
===Hop Resistance===
''Pediococcus'' species and strains are generally resistant to hop compounds, and have been reported to grow in beer with at least 30 IBU <ref name="Geissler"></ref>, and together with ''Lactobacillus'' are reported to be responsible for ~70% of all beer spoilage incidents caused by microbes <ref name="Garcia-Garcia">[http://onlinelibrary.wiley.com/doi/10.1002/jib.397/abstract Pediococcus damnosus strains isolated from a brewery environment carry the horA gene. Jorge Hugo Garcia-Garcia, Luis Cástulo Damas-Buenrostro, Juan Carlos Cabada-Amaya, Myriam Elias-Santos, Benito Pereyra-Alférez. 2017. DOI: 10.1002/jib.397.</ref>. It has been suggested by research that horizontal gene transfer (transfer of genetic material by means other than reproduction) allows ''Pediococcus'' species (and other LAB) to obtain the genes associated with resistance to hops (primarily multi-drug transporter "horA", along with "hitA", "horC", and "horB", and ORF5 <ref name="Garcia-Garcia" />). This has been thought to allow ''Pediococcus'' to adapt to living in beer <ref name="Garcia-Garcia" /><ref name="Snauwaert"></ref>.
While able to grow in the presence of hops, the presence of hops still inhibits ''P. damnosus''. For example, one study found that in the presence of 15 IBU, lactic acid production was reduced by ~82%. Exposure to 15 IBU also increased diacetyl production by 350%, while 2,3-pentanedione (buttery, nutty, toasted, caramellic, diacetyl and acetoin notes <ref>[http://www.thegoodscentscompany.com/data/rw1003991.html "acetyl propionyl ". The Good Scents Company. Retrieved 01/18/2017.]</ref>) was decreased by 25%. Interestingly, exposure to 3% ABV and no hops reduced the production of diacetyl and 2,3-pentanedione by about 20%. The addition of vitamins, specifically thiamine (vitamin B1) and riboflavin (vitamin B2), increased the production of lactic acid in the presence of 15 IBU or no hops by about 15-30%. However, thiamine also increased diacetyl production by 100-125% and 2,3-pentadione production by 20-30% without the presence of hops. In the presence of 15 IBU, thiamine and/or riboflavin increased diacetyl production by about 26-36% and 2,3-pentadione by about 40-114% <ref>[http://onlinelibrary.wiley.com/doi/10.1002/jib.385/full The influence of thiamine and riboflavin on various spoilage microorganisms commonly found in beer. Barry Hucker, Melinda Christophersen, Frank Vriesekoop. 2017.]</ref>. Strains that are grown exposed to small amounts of iso-alpha acids can be adapted to survive higher amounts up to ~150 μg mL<sup>1</sup>. The implications of this in brewing mean that the bacteria can enter any stage of the process and remain in undetectable amounts until it adapts to higher IBU conditions and then potentially spoils beer <ref name="Garcia-Garcia" />.
==Storage==