Tetrahydropyridine

Tetrahydropyridine (THP) and related compounds are formed by microbes, and these compounds give an off flavor that tastes grainy like Cheerios® or Cap'n Crunch® cereal, or sometimes "mousy" like animal urine. However, a significant number of people cannot taste these compounds.

THP is only produced by "wild" microbes like Brettanomyces and lactic acid bacteria such as Lactobacillus. It mainly occurs when packaging, when production is stimulated in the presence of oxygen +/- fermentable sugar. Therefore THP is a significant concern in sour beer production, since these microbes are commonplace.

The best strategies to avoid the production of THP are:

1. Avoid excessive oxygen exposure prior to packaging and during packaging. (For beer, see low oxygen brewing cold-side methods)
2. Add yeast from an acid shock starter at the time of packaging.
3. In wine, proper usage of sulfite should control the wild microbes.
4. Passivation of all stainless steel that comes into contact with the wort, beer, wine, etc. would theoretically be helpful, along with the use of RO water in brewing. These measures help limit iron, which is required for THP production.

If THP forms, it typically ages out over a period of months, but it may take longer.

See THP on the Milk the Funk wiki for more information.