Well, after nearly 50 brews, this is the first time that I have encountered a contamination in the brewing process. I am very careful about sanitising everything that comes into contact with the wort/beer. I use ChemSan (used to be StarSan) in a spray bottle. Same as most commercial brewers, but I must have missed something!
Brew number 45 (Deanhouse Blonde IPA) was bottled just over a week ago. It is bottled conditioned so after a week in the warm, it was ready to be put in the cellar. However, I thought I would have a quick taste before storing it in the cellar.
It hadn’t quite cleared which was a bit odd. It was also slightly darker than other versions of the same brew. Again, a bit odd. On tasting, it had a strange off taste – it smelt slightly like phenol. I opened a second bottle – it was the same. And a third bottle with the same aftertaste confirmed there was a problem.
A bit of research on the web revealed that this was probably a wild yeast contamination. Looking back at my notes, I should have realised there was a problem earlier in the process. This brew had a final gravity (FG) of 1.003! Way under what it should have been. See here for more on differences in gravity readings. That was a good clue that there was a problem.
The contamination must have occured either when transferring the wort into the fermenter or in the fermenter itself. Lesson learnt.
The next brew 46 (Gamma Ray clone) cleared perfectly and had a good FG. Brews number 47 and 48 similarly finished on the correct final gravity. So I suspect these will be ok too. But I haven’t tasted them yet. [Update: I have now, I these brews are fine too!]
Hopefully, this was just a one off, but an important lesson to learn. I will put this one down to experience. The brew went down the drain (literally) and all the bottles sanitised.