Changes

Forms of '''Tetrahydropyridines''' (abbreviated and often referred to generically by brewers as '''THP'''), specifically 2-acetyl-3,4,5,6-Acetyltetrahydropyridine and 2-acetyl-2,31,4,5,6-tetrahydropyridine (abbreviated ATHP or ACTPY), 2-ethyltetrahydropyridine (abbreviated ETHP or ETPY), and 2-acetyl-1-pyrroline (abbreviated ACPY or APY) <ref name="wikipediaSnowdon">[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, and the aftertaste can remain for a few minutes. Not all people are able to detect this the flavor, and a of THP. The low pH of sour beer or wine makes it harder to detect the flavor and often impossible to detect the aroma. An increase in pH is needed in order to detect the off-flavor, and the mouth's salivary pH serves that purpose when tasting beer or wine with THP. This effect on sensory detection by low pH might also explain why some people are better at detecting it since people have different pH's on the surface of their tongues and saliva <ref name="Snowdon">[http://pubs.acs.org/doi/abs/10.1021/jf0528613 Mousy Off-Flavor: A Review. Eleanor M. Snowdon, Michael C. Bowyer, Paul R. Grbin, and Paul K. Bowyer. 2006.]</ref>. Diacetyl is sometimes mistakenly indicated as a potential cause of this flavor in sour beers. However, Tetrahydropyridines are the accepted cause. The flavor tends to age out of sour beers after 2-6 months in the fermenter, kegs, or bottles. The exact mechanism for this is not fully understood, and it is unknown whether cold or room temperature storage speeds up the breakdown process (it is more likely that room temperature storage will result in faster breakdown of THP) <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>. Many brewers have noticed that pitching rehydrated wine yeast at packaging reduces the amount/duration of this flavor in kegs and bottles <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>.

ATHP (which has two forms: 2-acetyl-3,4,5,6-tetrahydropyridine and 2-acetyl-1,4,5,6-tetrahydropyridine) has a much lower flavor threshold than ETHP (see [[Tetrahydropyridine#Thresholds_and_Quantities_Found_in_Mousy_Wine|Thresholds]]), and has been historically cited as the cause of mousy off-flavors detected in wine. In wine, its aroma cannot be detected due to the low pH of wine (it can be detected if the pH is raised), only the flavor. It is easier to detect in higher pH wines. ATHP is the form of THP that is the major contributor to the aroma of freshly baked bread, corn tortilla chips, and crackers. How different foods/wines/beers interact with ATHP on the palate may explain the different flavors that are detected by people, as well differing concentrations and peoples' ability to detect ATHP <ref name="Snowdon"></ref>.