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added notes about butyric acid production, role of oxygen, and acetaldehyde issues as per Bryan Heit
===Sugar Utilization and Secondary Metabolites===
For a chart and in depth discussion on what types of sugars are fermentable by different species of ''LactobaccilusLactobacillus'', as well as charts on ''secondary metabolites'', see [http://phdinbeer.com/2015/04/13/physiology-of-flavors-in-beer-lactobacillus-species/ Matt Humbard's ''Physiology of Flavors in Beer – Lactobacillus Species'' blog article]. Heterofermentative species can also produce [[Tetrahydropyridine]].
In summary:
* All types of ''Lactobacillus'' produce different levels of secondary metabolites (compounds that are not required for the organism to live <ref>[http://en.wikipedia.org/wiki/Secondary_metabolite Secondary Metabolite. Wikipedia. Retrieved 6/9/2015.]</ref>) in addition to the primary metabolites discussed above. These include acetaldehyde, diacetyl, fusel alcohols, and many more compounds (see [http://phdinbeer.com/2015/04/13/physiology-of-flavors-in-beer-lactobacillus-species/ Matt's article] for more details).
* Despite some beliefs by brewers, ''Lactobacillus'' has not been shown to produce significant levels [[Butyric Acid|butyric acid]] (see the [[Butyric Acid|butyric acid]] page for more information) in the presence of oxygen or otherwise in brewer's wort. Some species might be able to produce small amounts of [[Isovaleric_Acid|Isovaleric Acid]] in the presence of ''Streptococcus thermophilus'' or another alpha-keto acid producing microorganism (see the [[Isovaleric Acid]] page for details). * Although ''Lactobacillus'' are not not inhibited by oxygen, they are generally not considered to be organisms that produce oxygen-dependent metabolites. Some heterofermentative species produce acetic acid, butyric acid (not much in wort, but more so in fermented milk products), and propanoic acid, but they always do so through an anaerobic pathway. The presence of oxygen does not affect metabolism in general <ref name="heit_oxygen_LAB">[https://www.facebook.com/groups/MilkTheFunk/permalink/1182597671768445/?qa_ref=qd&comment_id=1182773928417486&reply_comment_id=1183047521723460&comment_tracking=%7B%22tn%22%3A%22R9%22%7D Conversation with Bryan Heit on the effects of oxygen in LAB on MTF. 11/23/2015.]</ref>. * The major off-flavor that some ''Lactobacillus'' strains might produce is acetaldehyde <ref name="heit_oxygen_LAB"></ref>. ''Saccharomyces'' will help to metabolize the acetaldehyde produced by ''Lactobacillus''.
===Foam Degradation===