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→Chemical and physical properties
===ETHP===
2-ethyltetrahydropyridine has the highest odor thresholds of the forms of THP found in lambic at around 150 ug/L and has a flavor threshold around 3 ug/L in "mousey wines", though it may be higher in other contexts<ref name=Snowdon> Snowdon, EM; Bowyer, MC; Grbin, PR; and Bowyer, PK [Mousy http://pubs.acs.org/doi/pdf/10.1021/jf0528613 | Mousey Off-Flavor: A Review], 2006</ref>. Lactic acid bacteria may produce it in detectable concentrations.
ETHP may also be formed by the metabolism of ATHP by Brettanomyces over long time periods, which may explain why THP odors and flavors often drop off in beers where Brettanomyces is present due to higher odor and flavor thresholds of ETHP compared to ATHP. However, this is controversial.
===ATHP===
2-acetyltetrahydropyridines are much easier to smell (odor threshold ~1.6 ug/L<ref name=Snowdon> Snowdon, EM; Bowyer, MC; Grbin, PR; and Bowyer, PK [http://pubs.acs.org/doi/pdf/10.1021/jf0528613 | Mousey Off-Flavor: A Review], 2006</ref>) than ETHP, though its flavor threshold is similar at ~5 ug/L (minimum). However the low pH of the beer may prevent the odor of ATHP from being detected. The flavor, however, remains present.
===APY===
2-acetylpyrroline has the lowest odor and flavor threshold of the three primary forms of THP found in lambic (odor ~100 pg/L, flavor down to "trace amounts"<ref name=Snowdon> Snowdon, EM; Bowyer, MC; Grbin, PR; and Bowyer, PK [http://pubs.acs.org/doi/pdf/10.1021/jf0528613 | Mousey Off-Flavor: A Review], 2006</ref>), and is primarily produced by lactic acid bacteria.
==In Lambic==