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added section for off-flavor considerations
==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 <ref name="Fenaroli_ethylisovalerate">[https://books.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. CRC Press, Dec 3, 2004. Pg 587.]</ref><ref name="Joseph">[http://www.ajevonline.org/content/suppl/2015/07/28/66.3.379.DC1/Supplemental_Data.pdf Supplemental 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, as far as the authors of this wiki know. See also [[Brettanomyces#Ester_Production|Brettanomyces ester production]].
==Status as an Off-Flavor==
Isovaleric 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, many brewers find small amounts to be acceptable in mixed fermentation sour beers and lambics. Other brewers consider any amount of isovaleric acid to be an off-flavor and a sign that the 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 at what amounts. 08/08/2020.]</ref.
==References==