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==Metabolism==
===Growth and Environment===
''Pediococcus'' generally has a high tolerance to ethanol compared to other bacteria, and can range from 10-25% ABV, depending on the species and strain. ''P. damnosus'' is sensitive to warm temperatures. It is unable to grow at 35°C or higher. The optimal growth occurs at 22°C. Other species can be more tolerant of higher temperatures, for example, ''P. parvulus'' and ''P. inopinatus'' have been shown to grow between 12 to 40°C, with rapid death occuring at 45°C <ref name="Wade_2018" />. ''P. damnosus'' is sensitive to environments that contain NaCl, and will not grow with concentrations of 4% NaCl <ref name="ucdavis"></ref>. Most strains of ''P. claussenii'' can grow in beer. About half of the strains tested of ''P. damnosus'' can grow in beer, and none to very few strains of ''P. acidilactici'', ''P. parvulus'', and ''P. pentosaceus'' have been found to grow in finished beer.
''Pediococcus'' and other lactic acid bacteria have a wide range of resistance to SO<sub>2</sub> depending on species and strain. One study by Edwards and Jensen (1992) reported that ''P. parvulus'' was able to thrive in 20 mg/L of free SO<sub>2</sub> (0.39 mg/L molecular SO<sub>2</sub>), indicating that small amounts of SO<sub>2</sub> are not enough to inhibit ''Pediococcus''. Other studies have shown that different strains can be inhibited at concentrations between 100-256 mg/L total SO<sub>2</sub> <ref name="Wade_2018" />.
===Lactic Acid Production===
[[File:Pedio sugars.JPG|right|Pedio fermentables <ref>Wine Microbiology. Practical Applications and Procedures. Kenneth C. Fugelsang, Charles G. Edwards.</ref>]]
About 90% of sugar metabolized by ''Pediococcus'' produces both L- and D-lactic acid <ref name="Wade_2018" />. It does so by homolactic fermentation producing primarily lactic acid (same EMP pathway as [[Lactobacillus#Types_of_Metabolism|''Lactobacillus'' homolactic fermentation]]), although some species/strains can convert glycerol to lactic acid, acetic acid, acetoin, and CO2 under aerobic conditions (''P. damnosus'' is not in this category) <ref>[https://books.google.com/books?id=1b1CAgAAQBAJ&pg=RA2-PA1&lpg=RA2-PA1&dq=pediococcus+damnosus+homolactic&source=bl&ots=myI2alVB78&sig=cG-yWB4GuABQFEtqD2CAyKmU0TE&hl=en&sa=X&ved=0CEAQ6AEwBGoVChMI66C5593-xgIVCVKICh3Pcg7c#v=onepage&q=pediococcus%20damnosus%20homolactic&f=false Encyclopedia of Food Microbiology. Pediococcus. Carl A. Batt. Academic Press, Sep 28, 1999 .]</ref>. Some strains of ''P. pentosaceus'' can ferment five-chain sugars such as xylose to produce acetic acid and lactic acid. Some strains of ''P. halophilus'' (now reclassified as ''Tetragenococcus halophilis'') can convert citric acid into acetic acid and oxaloacetate (oxaloacetate is then further reduced to acetic acid and diacetyl, and the diacetyl is further reduced to acetoin, and 2,3-butanediol) by producing citrate lyase enzyme. This generally occurs at a slower rate than malolactic fermentation and depends on pH and temperature. However, all species in the ''Pediococcus'' genus are considered obligatory homofermentative because of the pathways that they use <ref>[http://aem.asm.org/content/81/20/7233.full A Genomic View of Lactobacilli and Pediococci Demonstrates that Phylogeny Matches Ecology and Physiology. Jinshui Zheng, Lifang Ruan, Ming Sun and Michael Gänzle. 2015.]</ref><ref name="Wade_2018" /><ref>[https://aem.asm.org/content/53/6/1257.short Citrate Metabolism by Pediococcus halophilus. Chiyuki Kanbe, Kinji Uchida. 1987.]</ref>.
===Malolactic Fermentation===
See the [[Cider#Microbes|Cider]] page.
===Carbohydrate Metabolism===
[[File:Pedio EMP Pathway.jpg|thumb|200px|right|[https://onlinelibrary.wiley.com/doi/full/10.1111/ajgw.12366 Homofermentative Embden–Meyerhof–Parnas (EMP) pathway for the production of lactic acid, acetoin, diacetyl and 2,3‐butanediol and acetic acid production from citrate metabolism. Image by Wade et al (2018).]]]
''P. damnosus'' can ferment glucose, sucrose, and galactose. Some strains of ''P. damnosus'' can ferment maltose and sucrose <ref name="ucdavis"></ref>. The disaccharide trehalose is the preferred carbon source for Pediococci <ref name="Geissler"></ref>. While simple sugars are the primary food source for ''Pediococcus'', many strains of ''P. damnosus'' have been observed to produce varying degrees of both alpha and beta-glucosidase enzymes. Alpha-glucosidase enzymes have the ability to break down higher chain sugars, including dextrins, starches, and glucans (possibly even the glucans that are produced by ''P. damnosus'' that result in ropy beer). The types of beta-glucosidase enzymes produced by ''P. damnosus'' are thought to perhaps play a role in breaking down monoglycosidic bonds (see [[Glycosides]]), but cannot break down the more complex diglycosidic bonds which are needed to break down many glycosides that would release flavor and aroma compounds. Compared to the microbe ''Oenococcus oeni'' which is often used in wine and cider fermentation (malolactic fermentation) and has been shown to have more impactful beta-glucosidase activity, ''P. damnosus'' is thought to be less impactful on glycosides. Unlike ''O. oeni'' which decreases its enzymatic activity in low pH conditions, enzymatic activity of ''P. damnosus'' is very stable at a pH of 3-4. Very low concentrations of glucose or fructose (1 g/l) inhibit this enzymatic activity in ''P. damnosus''. The presence of alcohol inhibits the alpha-glucosidase activity in most strains, which might contribute to longer lasting ropiness in beer. The optimal temperature for enzymatic activity in ''P. damnosus'' is between 35-40°C (95-104°F) <ref>[http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2005.02707.x/full Screening of Lactobacillus spp. and Pediococcus spp. for glycosidase activities that are important in oenology. A. Grimaldi, E. Bartowsky, V. Jiranek. 2005. DOI: 10.1111/j.1365-2672.2005.02707.x.]</ref>.
==="Ropy" or "Sick" Beer===