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==Introduction=='''Isovaleric Acid''', also known as 3-Methylbutanoic acid, is an organic compound with the formula (CH3)2CHCH2CO2H. The flavor and aroma are often described as rancid Parmesan, "pungent cheese" or "foot odor". it It is not to be confused with [[Butyric Acid]], which specifically has a more bile or vomit aroma and flavor. The flavor threshold of isovaleric acid has been reported to be 1 mg/L <ref name="aroxa">[http://www.aroxa.com/beer/beer-flavour-standard/isovaleric-acid/ Aroxa. Isovaleric acid. Retreived 12/30/2015.]</ref> and 1.5 mg/L <ref name="peyer_2017" />. It has a boiling temperature of 347-351°F (175-177°C) <ref name="wikipedia" />. ==Production in Beer and Wine==''[[Brettanomyces]] '' can create isovaleric acid <ref name="wikipedia">[http://en.wikipedia.org/wiki/3-Methylbutanoic_acid Wikipedia article]</ref>. The compound generally takes a few months to produce in beer by ''Brettanomyces''. ''Brettanomyces'' breaks down leucine present in beer into isovaleric acid (controversial, but generally accepted) <ref>[https://scholar.sun.ac.za/bitstream/handle/10019.1/4141/Botha,%20J.J.pdf?sequence=1 Botha, Janita J. Sensory, chemical and consumer analysis of ''Brettanomyces'' spoilage in South African wines. March 2010. Pg 2, 13, 17, 18]</ref><ref>[https://scholar.sun.ac.za/bitstream/handle/10019.1/1239/oelofse_investigating_2008.pdf?sequence=1 Oelofse, Adriaan. Investigating the role of ''Brettanomyces'' and Dekkera during winemaking. December 2008.]</ref>. Isovaleric acid can also be produced by a bacteria that lives naturally on human skin and is responsible for foot odor called Staphylococcus epidermidis. It does so by degrading leucine, an amino acid present in sweat <ref>[http://www.ncbi.nlm.nih.gov/pubmed/16699586 Ara K, Hama M, Akiba S, Koike K, Okisaka K, Hagura T, Kamiya T, Tomita F. Can J Microbiol. 2006 Apr.]</ref>. Leucine is also present in beer <ref>[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1981.tb03992.x/pdf Hall, Nutfield, Redhill, Surrey. Amino Acid Esters in Beer. Brewing Research Foundation. July 14, 1980.]</ref>. Brettanomyces also breaks down  It has been shown in Swiss-type cheese that other bacteria, including species and strains of ''Streptococcus'' (more so) ''Lactobacillus'' (less so) can produce various amounts of isovaleric acid from leucine present in beer into , as well as other compounds from other carboxylic acids. ''Lactobacillus'' is not capable of producing isovaleric acid without the presence of an [https://en.wikipedia.org/wiki/Keto_acid alpha-keto acid], which is produced by ''Streptococcus thermophilus'', so the presence of ''S. thermophilus'' or another alpha-keto acid producing microorganism is required for ''Lactobacillus'' to produce isovaleric acid (Controversialas well as a range of other acids). <ref>[http://aem.asm.org/content/70/7/3855.full Helinck, Le Bars, Moreau, and Yvon. Ability of thermophilic Lactic Acid Bacteria To Produce Aroma Compounds from Amino Acids.]</ref>. This has not been shown to occur in beer, but generally acceptedthis may be the reason that sour mashes often have a rancid cheese off flavor (although this may also be at least partially due to [[Butyric Acid]] production during [[Sour Mashing]]) <ref>[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1970.tb03256.x/pdf Green, C. P. The Volatile Water-Soluble Fraction Of Hop Oil. Aug 24, 1909.]</ref><ref>[https://scholarbooks.google.com/books?id=oWQdjnVo2B0C&pg=PA498&lpg=PA498&dq=oxidation+of+hop+resins+3-Methylbutanoic+acid&source=bl&ots=wmM8jX-qJY&sig=_wFzzuUA40eg0vMNc-7vfU6tneA&hl=en&sa=X&ei=XX2PVJHDI4bcoATjoYK4BA&ved=0CEcQ6AEwBQ#v=onepage&q=oxidation%20of%20hop%20resins%203-Methylbutanoic%20acid&f=false Oliver, Garret. The Oxford Companion to Beer. 2001. Pg 498.]</ref>. ===Kettle Souring===Professional brewer Khristopher Johnson has observed the taste of isovaleric acid in kettle soured beers. Purging with CO2 has been quoted as something that has resolved this issue, the hypothesis being that oxygen could promote the formation of isovaleric acid if aerobic contaminates are present <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1778865588808314/?comment_id=1778870915474448&comment_tracking=%7B%22tn%22%3A%22R9%22%7D Khristopher Johnson. Milk The Funk Facebook group. 08/03/2017.]</ref>.sun  One study compared the levels of isovaleric acid in a kettle soured beer (flushed with CO2), a sour mashed beer (flushed with CO2), and a beer co-fermented with ''Lactobacillus amylovorus'' and US-05.ac They found that there was a significant increase in isovaleric acid when the ''Lactobacillus'' and US-05 were co-fermented (see the table below).za The authors suggested that this might be due to the release of the amino acid precursors by the ''Lactobacillus'' towards the end of its life cycle when it was allowed to survive in a co-fermentation, versus being killed in the kettle souring/bitstreammash souring batches <ref name="peyer_2017">[http:/handle/10019www.asbcnet.1org/publications/journal/vol/2017/4141Pages/BothaASBCJ-2017-3861-01.aspx Sour Brewing: Impact of Lactobacillus amylovorus FST2.11 on Technological and Quality Attributes of Acid Beers. Lorenzo C. Peyer, Martin Zarnkow, Fritz Jacob, David P. Schutter,%20JElke K. Arendt. 2017.J]</ref>.pdf?sequence {| class="wikitable sortable"|-! Method !! Amount of IVA (mg/L) <ref name="peyer_2017" />|-| US-05 Only (control) || 0.83|-| Mash Souring with ''L. amylovorus'' and primary fermentation with US-05 || 0.72|-| Kettle Souring ''L. amylovorus'' and primary fermentation with US-05 || 0.50|-| Co-fermentation with ''L. amylovorus'' and US-05 || 1 Botha.15|-|} ==Other Producers==Other bacteria have been shown to create isovaleric acid, Janita Jand may contribute to the production of it in beer in unsanitary conditions. Sensory''Bacillus amyloliquefaciens'' and ''B. atrophaeus'' are Gram-positive, chemical aerobic (require oxygen for growth) bacteria and consumer analysis have been shown to produce isovaleric acid <ref name="Vasquez">[http://bashanfoundation.com/gmaweb/pdfs/vazquez1.pdf Phosphate-solubilizing microorganisms associated with the rhizosphere of Brettanomyces spoilage mangroves in South African winesa semiarid coastal lagoon. P. Vazquez, G. Holguin, M.E. Puente, A. Lopez-Cortes, Y. Bashan. 2000.]</ref><ref>[http://web.mst.edu/~microbio/BIO221_1998/B_amylo.html Bacillus amyloliquifaciens. Carl Sather's website. Retrieved 10/06/2015.]</ref><ref>[http://www.researchgate.net/publication/263432119_Bacillus_atrophaeus_main_characteristics_and_biotechnological_applications__a_review Bacillus atrophaeus: main characteristics and biotechnological applications – a review. Sandra R B R Sella, Luciana Vandenberghe, Carlos Ricardo Soccol. 2014.]</ref>. ''Xanthobacter agilis'' is a Gram-negative aerobic bacteria that can produce isovaleric acid <ref name="Vasquez"></ref><ref>[http://www.thelabrat.com/restriction/sources/Xanthobacteragilis.shtml Xanthobacter agilis. The Lab Rat. Retrieved 10/06/2015.]</ref>. ''Paenibacillus macerans'' is a facultative anaerobe (can utilize oxygen if present, but oxygen is not required) that can produce isovaleric acid. ''P. macerans'' is a Gram-variable bacteria, meaning that it can produce Gram-positive and Gram-negative rods <ref>[https://en.wikipedia.org/wiki/Paenibacillus_macerans Paenibacillus macerans. Wikipedia. March 2010Retrieved 10/06/2015.]</ref>. Pg 2The strict anaerobe, ''Megasphaera cerevisiae'', which has been identified as a beer spoiler, can also produce isovaleric acid (as well as [[Butyric_Acid|butyric acid]], 13valeric acid, 17caproic acid, 18and hyrodgen sulfide) <ref>[http://www.asbcnet.org/publications/journal/vol/2016/Pages/ASBCJ-2016-4895-01.aspx Monoclonal Antibodies Binding to Lipopolysaccharide from the Beer-Spoilage Bacterium Megasphaera cerevisiae Exhibit Panreactivity with the Strictly Anaerobic Gram-Negative Brewing-Related Bacteria. Barry Ziola. 2016.]</ref>. ===Hops===Isovaleric acid can also be produced by the oxidation of hops, and is often found in hops aged for traditional [[lambic]] brewing. See [[Hops#Aged_Hops|Aged Hops]] for more information. ==Metabolic Breakdown==''Brettanomyces'' can break down isovaleric acid into an ester called ethyl isovalerate. This ester is described as fruity, sweet, berry-like with a ripe, pulpy fruit nuance <refname="Fenaroli_ethylisovalerate">[https://scholarbooks.google.com/books?id=15HMBQAAQBAJ&pg=PA638&lpg=PA638&dq=ethyl+valerate+threshold&source=bl&ots=avVr8PQQ_p&sig=zm81_lhLU86VJ4jBNnm4I9nnxDw&hl=en&sa=X&ved=0CDIQ6AEwBGoVChMImYrEl6usxwIVAjmICh1HGwEs#v=onepage&q=ethyl%20isovalerate%20threshold&f=false Fenaroli's Handbook of Flavor Ingredients, Fifth Edition. George A. Burdock.sun CRC Press, Dec 3, 2004.ac Pg 587.za]</bitstreamref><ref name="Joseph">[http:/handle/10019www.ajevonline.1org/content/suppl/2015/07/28/123966.3.379.DC1/oelofse_investigating_2008Supplemental_Data.pdfSupplemental Data for: Joseph, C.M.L., E.A. Albino, S.E. Ebeler, and L.F. Bisson. Brettanomyces bruxellensis aroma-active compounds determined by SPME GC-MS olfactory analysis. 2015.]</ref><ref name="lucy_joseph">[http://slideplayer.com/slide/4473144/ Impact of Brettanomyces on Wine. Presentation by Lucy Joseph of UC Davis. Retrieved 08/15/2015.]</ref>. The rate of metabolic breakdown of isovaleric acid into ethyl isovalerate has not been researched, but anecdotes from brewers indicate that only very small amounts of isovaleric acid seem to be broken down over time, and ''Brettanomyces'' will not significantly "clean up" a beer with high amounts of isovaleric acid <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/4384393781588802/?sequencecomment_id=4386457104715803 Richard Preiss and other brewers. MTF post; anecdotes on isovaleric acid break down over time. 03/09/2021.] </ref>. See also [[Brettanomyces#Ester_Production|''Brettanomyces'' ester production]]. ==Status as an Off-Flavor==1 OelofseIsovaleric acid is widely thought to be an off-flavor in beer, particularly non-sour beer. It is also generally thought of as an off-flavor in kettle sours and in some mixed fermentation beers. However, Adriaanmany brewers find small amounts to be acceptable in mixed fermentation sour beers and lambics. Investigating Other brewers consider any amount of isovaleric acid to be an off-flavor in mixed fermentation sour beers and lambic, and they consider it a sign that the role of Brettanomyces beer has not been allowed to age long enough <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/3752511238110396 Milk The Funk poll on whether or not isovaleric acid is considered an off-flavor and Dekkera during winemakingat what amounts. December 200808/08/2020.]</ref>.