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''[[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>. In one study on mixed fermentation sour beer with one strain each of L. brevis, B. bruxellensis, and S-04, researchers found that isovaleric acid was not detectable until month 12 of aging, at which point it was detected above flavor threshold <ref>[https://www.mdpi.com/2076-2607/11/7/1681 Postigo, V.; García, M.; Arroyo, T. Study of a First Approach to the Controlled Fermentation for Lambic Beer Production. Microorganisms 2023, 11, 1681. https://doi.org/10.3390/microorganisms11071681.]</ref>.