Beer 201: Tetrahydropyridine

I like to call this one, “Excuse me, waiter? There’s some Cheerios in my beer.”

Time to drop some knowledge. So, remember the sour beer festival that I went to a few months back? Well, I ran into something that I hadn’t really been able to pin down before: sometimes, some sour beers tasted… weird. There was an aftertaste there. Something wheaty and kind of unpleasant. But I couldn’t place it.

Then my friend M said, “Ew, this one tastes like Cheerios” and everything fell into place. Cheerios! That was exactly the weird taste that I’d been getting! But what the heck would cause this kind of strange flavor that, in my opinion, clearly didn’t belong there? It was time for some Google fu.

There is a chemical compound called Tetrahydropyridine, produced by some yeasts*, that is responsible for this imperfection in the flavor of beers – and it is generally considered by brewers and wine makers (who battle this off flavor, too) to be a flaw. Brewers usually abbreviate it to THP (thank goodness, because that is not a word I feel like typing for a second time) and it is considered a ketone (which is something I actually know a bit about because of a diet I followed for years… ANYWAY). It is responsible for the Cheerios, biscuit/cracker, or – according to some people – urine-like “off” flavors in sour beers.

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What I have experienced the most is a Cheerios/dry wheat taste on the back end of a beer taste or as an aftertaste that lingers. This is apparently a pretty common experience… except I’ve read that not everyone is able to detect this funky flavor. The acidity/low pH of sour beers can mask or overwhelm the flavors (and usually the aroma, too) of THP. Since everyone’s tongue has a slightly different natural pH level itself, some folks’ mouths will cause an increase in the pH of the liquid and they will be able to taste the THP’s effects; some people’s natural pH levels won’t cause enough of change in the beer to reveal this flavor. I have a pretty attuned palate, generally speaking, so I’m not surprised that I’m sensitive enough to detect this kind of weirdness.

It sounds like aging beers will reduce or remove this flavor, in bottles, kegs, or fermenters. But this can take a few months’ time and small breweries, especially, don’t have the money or time to just sit on a beer – they have more beer to make and ship as soon as possible. I would bet money that sour beers from smaller breweries with more limited storage are more likely to have this problem.

Now, I wouldn’t say that this is a common problem; most sour beers I’ve tried don’t have this flaw. But the ones that do? Well, they stick out in my memory as being particularly off-putting. Would I send back a beer with this taste? Probably not. But I also just might not finish the glass and move on to something else.

*Brettanomyces, which is popular for sour beers and wild ales, is a common culprit for producing THP. Lactic Acid Bacteria and Acetic Acid Bacteria can also yield the compound.

 

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