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, lactic acid bacteria such as Lactobacillus, and acetic acid bacteria. It mainly occurs around the time of packaging, when production is stimulated in the presence of oxygen +/- fermentable sugar. THP is a significant concern in sour beer production, where 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. For carbonated beverages: Naturally carbonate rather than force carbonate, and add yeast from an acid shock starter at the time of packaging.
3. 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.
4. In wine, proper usage of sulfite should inhibit the wild microbes that would otherwise produce THP.

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.