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Forms of '''Tetrahydropyridine''' (specifically 6-Acetyl-2,3,4,5-tetrahydropyridine [<nowiki />ATHP/or ACTPY], 2-ethyltetrahydropyridine [<nowiki />ETHP], and 2-acetyl-1-pyrroline [<nowiki />ACPYor APY] <ref name="wikipedia">[http://en.wikipedia.org/wiki/6-Acetyl-2,3,4,5-tetrahydropyridine 6-Acetyl-2,3,4,5-tetrahydropyridine. Wikipedia. Retrieved 3/210/2015.]</ref>, which are classified as ketones <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1034461653248715/?comment_id=1034611563233724&offset=0&total_comments=29 Humbard, Matt. Milk The funk Discussion. 3/10/2015.]</ref>) are commonly attributed to the "mousy", "urine" (in high amounts) "cheerios" or "Captain Crunch" (in low amounts), "breakfast cereal", or more generically, "cracker biscuit" flavor in sour beers. The flavor is detected towards the end of the swallow. The exact cause of this perceived flavor is not definitive. Diacetyl has also been indicated as a potential cause to this flavor in sour beers. However, Tetrahydropyridines seem to be the most likely cause. The flavor tends to age out of sour beers, although the exact mechanism for this is not fully understood <ref>[http://www.homebrewtalk.com/f127/cheerios-character-after-bottling-504468/#post6516169 Tonsmeire, Michael. Homebrewtalk.com post 1. 11/21/2014. Retrieved 3/10/2015.]</ref>. Michael Tonsmeire also noticed that pitching rehydrated wine yeast at bottling reduces the amount/duration of this flavor <ref>[http://www.homebrewtalk.com/f127/cheerios-character-after-bottling-504468/#post6522207 Tonsmeire, Michael. Homebrewtalk.com post 2. 11/21/2014. Retrieved 3/10/2015.]</ref>.

[[Brettanomyces]], [[Lactobacillus]], and [[Pediococcus]] can produce forms of Tetrahydropyridines. In Brettanomyces, 2-acetyl-3,4,5,6-tetrahydropyridine (ATHP/ACTPY) can be metabolized by the amino acid L-Lysine and ethanol with oxygen having a stimulatory effect in it's production, although little else is known about it's production in Brettanomyces <ref>[http://www.brettanomycesproject.com/dissertation/introduction/ Yakobson, Chad. The Brettanomyces Project; Introduction. Retrieved 3/10/2015.]</ref>. ATHP is further metabolized into 2-ethyltetrahydropyridine (ETHP/ETPY) by Brettanomyces, although not much is known about this metabolic process either <ref>[http://ucce.ucdavis.edu/files/repositoryfiles/Joseph_5_Aromatic_Diverswity_of_Brettanomyces-82350.ppt Joseph, C.M. Lucy. ''Aromatic Diversity of Brettanomyces''. U.C. Davis. Retrieved 3/10/2015.]</ref>.