Bad Taste in Mouth

We popped into a CAMRA BF recently. One of our beers on so I thought I'd check it out. Nice to see it was on handpull.

But, oh dear, what's this? An unpleasant musty taint. "Right" says I, "I'll have a taste of that from the tap - not from the pump - if you don't mind" (I'm wearing one of our excellent T-shirts so it looks like I might be the brewer or something). And sure enough, it's the pump that's tainted, not the beer. I point this out. The clip is turned round. I retire. Fuming a little.

In a little while, a festival organiser strides over to me bearing two glasses. "Here", he says, "One from the pump - one from the tap". I gather it's some sort of test. I sniff, I sip. I firmly thrust the tainted one in his direction. "That one. Take it away."

Becky couldn't even take a sip.
Another brewer remarks that the beer smells to him like fresh trout. Not fishy. Earthy.
We discuss the earthy flavour of trout. He frowns when I mention eating stocked rainbow, as he fishes the rivers for the l'al brown jobs. I gather I'm a trout pleb. Or he's a trout snob, or something.

Over the next half hour I'm regaled with accounts of how thoroughly the pumps (which spend a lot of the year in storage) have been cleaned. And how carefully the beer is checked before connecting it to them.

Meanwhile there's a certain amount of checking from the pumps going on. A few more pumps are found to be tainted, and replacements rounded up. There's a couple of beers that won't be going on this evening, but all should be well the next day.

So, what shall we take home from this?

1. The musty taint that can build up in beer engines and lines can be difficult, or impossible, to remove by normal cleaning. These flavours have their source in bacterial (or fungal) growth and are detectable and offensive at homeopathically tiny (parts per trillion) levels. The chemicals responsible - geosmin, trichloranisole and others, seem to migrate into and through many plastics. So cleaning the surface - the inside of a pump or tube - might give you temporary relief, but a reservoir of taint lurks in the mass of the material to slowly diffuse back to the surface and into the contents. If the outside of plastic tube is contaminated, the mustiness will pass right through into the beer.
 We touched on this all some time ago.

 2. While the threshold for these off-flavours is very low, there's a wide range in individual sensitivity. If you're tasting beer for any purpose other than your own enjoyment you'll want to be sure that you're at least as sensitive as the bulk of drinkers.

3. Cleaning (pumps and lines) is not a magical operation.  It's a rational process that's easy to measure. Just having performed line cleaning does not of itself guarantee that the lines are fit for use.

4. Festival organisers - check the beer you're actually serving. Sure, don't put it on a pump until it's been checked at the tap.  But do check what's coming out of the pump. Every session.

5. Festival organisers - it's not neccessary to administer taste tests to brewers. Beer is what we do for a living. You're the amateurs. In the nicest possible way.