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There are, however, a few exceptions to this in the scientific literature. For example, ''L. plantarum'', which is a facultatively heterofermentative species, is homolactic without the presence of oxygen. In the presence of oxygen, however, ''L. plantarum'' switches to heterolactic fermentation, and further converts already present lactic acid already into acetic acid. In a lab setting the conversion of lactate to acetate only happened when glucose was no longer available (this may not be the case in wort where other limiting factors such as low pH can prevent ''L. plantarum'' from continuing their metabolic processes before all glucose is consumed). During the conversion of lactic acid to acetic acid, ''L. plantarum'' also produces hydrogen peroxide (H²0²), which is toxic to microorganisms and is thought to be a protection mechanism for ''L. plantarum'' <ref name="Quatravaux_plantarum"></ref><ref name="microbewiki_plantarum">[https://microbewiki.kenyon.edu/index.php/Lactobacillus_plantarum_and_its_biological_implications Lactobacillus plantarum and its biological implications. Microbe Wiki. Retrieved 6/7/2015.]</ref><ref name="shaner_plantarum"></ref>. Omega Yeast Labs reports that no noticeable acetic acid is produced if the oxygen is not purged with their OYL-605 ''Lactobacillus'' blend which contains ''L. plantarum'', and that brewers should not aerate wort during sour but purging O2 is not required (but do not aerate either) <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1222363364458542/?comment_id=1222371257791086&reply_comment_id=1225212894173589&comment_tracking=%7B%22tn%22%3A%22R%22%7D MTF conversation with Adi Hastings from Omega Yeast Labs on the effects of oxygen presence in OYL-605. 02/02/2016.]</ref>. ''L. brevis'' has been shown to increase growth rates in the presence of oxygen <ref name="brevis_aeration"></ref>.