Hi All,
It's happened again, that's four in a row. This time I'm using a brand new and meticulously cleaned bucket fermenter (and so it doesn't look as though the Fermzilla was the perp. as I suspected). I do think that I have pinpointed the point in the process where the infection has taken hold however, and it's weird.
There were a couple of issues on Brewday, I boiled off too much, leading to a hike in OG, and then fermented with a different strain of voss to the recipe, meaning a very slight under-attenuation. I tasted the brew after it had finished however and was very happy with the result (ESB, malty with nice orangey esters from the voss, no off flavours whatsoever). Immediately after tasting I cold crashed from 37c to 19c overnight, and then took it down to 2c the next morning. I was using a 3 piece airlock during fermentation, and switched this for a s shaped for the cold crash, regularly checking this to make sure that there was still sanitiser present in the airlock.
I tasted again a day after cold crashing was complete, and the beer had changed significantly. The off flavour/aroma from previous brews was there, and much of the character of the beer had disappeared. Elsewhere I've heard that infections disappear at lower temps, but this doesn't seem to be the case here, I'm pretty confident that all of my brews, both in Fermzilla (spunding valve) and bucket (airlock) have gone wrong at this stage. I'm confident that this is not (solely) due to oxidation, as I was previously using pressure ferm/transfer.
One point that I didn't think to mention before is my fermentation fridge, which is now the only piece of cold side equipment that I have not swapped out. I got this second hand off of Gumtree, and when I picked it up it absolutely stank. Someone had obviously spilt milk in it which was still present. The fridge had been unplugged for quite some time in a warm room prior to collection. I absolutely blitzed this with bleach, but a slight smell remains. I didn't really consider that this would be an issue, could this explain the incredible bad luck that I seem to have been experiencing, despite every attempt at sanitation? I still find it weird how this would only affect my beer post FG, and only become (noticeably) present once cold crashed.
I really appreciate you guys helping me out, apologies for asking you to do so again. I'm considering buying a new fridge as I want to eliminate this as a possibility. I was so bloody embarrassed when my wife told her family on a zoom meeting that I've cocked up another batch, and had to sit through them all laughing at me! I just want to actually have a reasonable tasting beer to show them to prove I'm not a complete idiot!