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'''Butyric Acid''' (chemical name '''butyrate''' <ref>[https://en.wikipedia.org/wiki/Butyrate Butyrate. Wikipedia. Retrieved 6/20/2015.]</ref>) is a carboxylic acid that is produced by anaerobic bacteria such as ''Clostridium butyricum'', ''C. kluyveri'', and ''Megasphaera spp'' <ref name="wikipedia">[http://en.wikipedia.org/wiki/Butyric_acid#Production Wikipedia description of Butyric Acid production]</ref> during glucose fermentation, and is generally considered an off flavor in sour beer. If not done right, [[Sour Mashing]] can be a big producer of butyric acid. Butyric acid is produced by anaerobic bacteria. The aroma and flavor is often described as a vomit, bile, or rancid cheese. It is also present in the human gut, and is the cause of the aroma of vomit <ref name="wikipedia"></ref>. This is not to be confused with [[Isovaleric Acid]] which has a more "feety" aroma and flavor. [[Brettanomyces]] can convert butyric acid into [[Ethyl Butyrate]] at low levels, which has a pineapple, tropical fruit aroma and flavor. Ethyl butyrate production occurred in only half of the ''Brettanomyces'' strains studied by Yakobson, with this conversion being less with the addition of lactic acid, indicating that ethyl butyrate conversion from butyric acid is strain dependent and slows in the presence of lactic acid <ref>[http://www.brettanomycesproject.com/dissertation/pure-culture-fermentation/pure-culture-fermentation-discussion/ "Pure Culture Fermentation Discussion." The Brettanomyces Project. Chad Yakobson. 2011. Retrieved 06/06/2016.]</ref><ref>[http://brettanomycesproject.com/dissertation/pure-culture-fermentation/impact-of-pitching-rate/ "Impact of Pitching Rate." The Brettanomyces Project. Chad Yakobson's . 2011. Retrieved 06/06/2016.] </ref><ref>[http://brettanomycesproject.com/dissertation/pure-culture-fermentation/impact-of-initial-concentration-of-lactic-acid/ "Impact of the Initial Concentration of Lactic Acid on Pure Culture Fermentation." The Brettanomyces DissertationProject. Chad Yakobson. 2011. Retrieved 06/06/2016.]</ref>. Butyric acid has shown to have some health benefits in medical research <ref>[http://jmm.sgmjournals.org/content/59/2/141.full Van Immerseel F, Ducatelle R, De Vos M, Boon N, Van De Wiele T, Verbeke K, Rutgeerts P, Sas B, Louis P, Flint HJ. Butyric acid-producing anaerobic bacteria as a novel probiotic treatment approach for inflammatory bowel disease. J Med Microbiol 2010;59:141–3.]</ref><ref>[http://iai.asm.org/content/8/1/30.full.pdf Effect of Colon Flora and Short-Chain Fatty Acids on Growth In Vitro of Pseudomonas aeruginosa and Enterobacteriaceae. MATTHEW E. LEVISON. 1973.]</ref>.