Changes

''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, but anecdotes from brewers indicate that only a small amount of isovaleric acid seem seems 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/?comment_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]].