What could that be? Dump beer down the drain.
I, like many others in Ireland, ferment in plastic. The convenient and cheap polypropylene bucket is the workhorse of amateur brewing in the UK and Ireland. We know there are drawbacks and have been told all about scratches in the seemingly smooth surface giving nasties places to hide but how serious can the risk really be? We have all tasted first class beers fermented in plastic. I have even heard of commercial microbreweries using polypropylene fermentors, so maybe the risk is a bit overstated. Well, I can now tell you, from bitter personal experience, that the risk is very real.
A few weeks ago I noticed an off flavour in one of my beers. My latest Belgian Double had a definite solvent-like tang to it which I put down to oxidation even though the beer was not actually very old yet. It was slight, but definitely there and while others didn't seem to notice, it spoiled the beer for me.
The next beer out of the fermentors was a Wheat Beer which I primed with maple syrup and once again it got that solvent-like flavour, WTF? The Bitter from the fermentor beside it turned out lovely and I was drinking it at three weeks old, but the Dark Wheat Beer which followed the Maple Wheat into the older of my two fermentors went south in the same way the Maple Wheat had.
By the time I twigged what was going on and ordered a replacement bucket for my older fermentor I had a Weiss bier in the older bucket and a Porter in the slightly less elderly one. You will not be surprised to hear that the Weiss ended up with the same infection but here is the sting in the tail: so did the Porter.
You see, most of my beers go straight from the primary into the keg, but there are some that I feel would benefit from a secondary fermentation, in which case I simply syphon from one bucket to the other. This has the effect of allowing whatever little nasties manage to inhabit one bucket the opportunity to colonise the other one too. This is exactly what happened to my second bucket, putting it just a little behind the first in developing into a beer hostile environment.
The bitter I mentioned earlier may even have had a slight touch of it, but it was consumed so young that the infection barely had time to do any damage. The fact that it had an enjoyable butterscotch-like diacetyl flavour, may also have helped to conceal any developing flaws.
The total list of casualties due to this infection is as follows: Maple Wheat, Dark Wheat, Weiss Bier, Porter. A total of 92 litres of beer down the drain and 23 litres of Belgian Double which others like but I do not.
So where do I go from here? I get new buckets and start again. The first one has already knocked out a bitter and now holds a blond beer, neither of which show any sign of infection. As soon as I get another bucket I will go right back to my former practice of using one as a secondary vessel if I see fit.
So what am I going to change in reaction to this experience? My buckets. I will write the date I bought them on the side to remind me of how old they are. I will look for discolouration or smells which might indicate uninvited guests, but regardless of how nice they seem, if a bucket is more than two years old it gets retired. I'm not sure if these measures are sufficient or over the top but they would have been enough to save the 92 litres of beer I had to dump.
That is what I should have done to begin with and I would advise anyone who ferments in plastic to do the same. These buckets are cheap, but they do have to be replaced periodically.