Changes

''[[Lactobacillus]]'' and other LAB produce butyric acid by breaking down lipids to fats. The low level of lipids in brewer's wort most likely limits butyric acid to insignificant levels in beer production. Butyric acid production by ''Lactobacillus'' is more significant in milk based fermented products such as yogurt and cheese <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1182597671768445/?qa_ref=qd&comment_id=1182773928417486&reply_comment_id=1183242405037305&comment_tracking=%7B%22tn%22%3A%22R7%22%7D Conversation with Bryan of Sui Generis Blog on MTF regarding butyric acid production by Lactobacillus. 11/23/2015.]</ref>. For example, one study on a strain of ''L. plantarum'' that was fermented in three different substrates (oats, barley, and wheat) showed no production of butyric acid <ref>[http://www.sciencedirect.com/science/article/pii/S0308814609004373 Volatile compounds produced by the probiotic strain Lactobacillus plantarum NCIMB 8826 in cereal-based substrates. Ivan Salmeron, Pablo Fuciños, Dimitris Charalampopoulos, Severino S. Pandiella. 2009.]</ref>. Due to the low amount of lipids in wort, compounds from the reduction of lipids in grain fermentations by lactic acid bacteria have not been studied <ref name="peyer_review">[http://www.sciencedirect.com/science/article/pii/S0924224415300625 Lactic Acid Bacteria as Sensory Biomodulators for Fermented Cereal-Based Beverages. Lorenzo C. Peyer , Emanuele Zannini , Elke K. Arendt. 2016.]</ref>.  A common brewing myth is that ''Lactobacillus'' produces butyric acid when exposed to in the presence oxygen, however, there is no biological basis or evidence for this claim (see [[Lactobacillus#Effects_of_Oxygen|effects of oxygen on ''Lactobacillus'']]). The lack of evidence for this claim is supported by Santeri Tenhovirta's masters thesis in Food Science from the University of Helsinki (2019). Tenhovirta soured wort with several species of ''Lactobacillus'', including ''L. delbruekii'', ''L. plantarum'', ''L. alimentarius'', ''L. brevis'', ''L. buchneri'' and ''L. rhamnosus''. During the two days of souring, the vessels were not purged of air, allowing the ''Lactobacillus'' to ferment under aerobic (containing oxygen) conditions. After two days of souring, US-05 was pitched to finish the fermentation (the soured wort was not boiled). None of the resulting beers had butyric acid, except for the ''L. delbruekii'' sample, but that sample never contained viable ''L. delbruekii'' (even at pitching time), and the butyric acid in that sample was hypothesized to be caused by some unknown contaminating microbe <ref name="Tenhovirta_masters">[https://helda.helsinki.fi/handle/10138/303018 The Effects of Lactic Acid Bacteria Species on Properties of Sour Beer. Santeri Tenhovirta; master thesis in Food Science from the University of Helsinki. 2019.]</ref><ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2724807184214145/?comment_id=2725477224147141&reply_comment_id=2725508117477385&comment_tracking=%7B%22tn%22%3A%22R%22%7D Santeri Tenhovirta. Milk The Funk Facebook group thread on his masters thesis and the lack of butyric acid production under O2 conditions. 06/14/2019.]</ref>.