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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>.
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. They found that there was a significant increase in isovaleric acid when the ''Lactobacillus'' and US-05 were co-fermented. 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/mash souring batches <ref name="peyer_2017">[http://www.asbcnet.org/publications/journal/vol/2017/Pages/ASBCJ-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, Elke K. Arendt. 2017.]</ref>.
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