Thursday, April 22, 2010

Eeuw, nasty.

I was in a pub recently, drinking some beer that we'd made. It's a particularly flavour-packed fairly high ABV little number with some quite forward esters bordering on the solventy (N.B. this wasn't a mistake - was intended). It had about 10 weeks on oak chips in stainless, then re-racked into our plastic casks where it passed another few months. It's been interesting.

But this one, eeuw, what's that nasty smell? Some people couldn't smell anything wrong. Becky didn't like it but couldn't name it. One person referred to laundry. I smelled damp cellar, musty, something.

I'm guessing that here we have a hint of
trichloroanisole (TCA). You'll observe that this looks a lot like those chlorophenols that come up when chlorine based sanitisers are allowed to come into contact with the beer (or with wood). It might be derived from an undetectable trace of chlorophenol, methylated by some kind of bug, giving us TCA, which is incredibly smelly - detectable at parts per trillion.

Our noses are all different, and thresholds for detection of TCA vary by orders of magnitude, which is to say that I might not be able to detect something that you find utterly horrendous. Also, many people get used to TCA quickly, so after a few sniffs, it might stop bothering you (or not).

It's quite possible that the bad smell had got into the beer via dispense equipment, or was even migrating through beer lines which might be perfectly clean on the inside, if they were in contact with some minging gunk.

To be on the safe side, we need to make sure that our casks aren't building up scale (or beerstone) which might be giving a home to bugs, or impeding the rinsing away of sanitisers.

Since we normally use a chlorinated caustic cleaner which doesn't have anything special to restrict scale in it, we're starting an acid wash on the casks - every few trips. This gave me an excuse to go shopping at one of our excellent local agricultural supply and engineers. I wanted a John Deere hat but all I got was this stupid milkstone remover.


HardKnott Dave said...

'tis a problem that you cannot be sure it's not the pub at fault. It does sound similar to a suborn line infection I had a couple of years ago at my pub.

StringersBeer said...

Ah well, better safe than sorry.

StringersBeer said...

Update: I've been reading up on this a bit. Seems the smart money is on TCA distorting yr smell perception (an effect y. can observe at v. low concs), and it's stuff like geosmin that's actually responsible for the earthy / musty smell. Whatever.