I've been brewing for 5 years, though I took one off before my last batch due to a move. I kickstarted my experience by jumping right into all grain brewing with a friend who had years of experience. I keg because 1) I like drinking 2) I like sharing and 3) bottling is annoying. Enough about me.
I recently brewed a pale ale, and a stout- both 5 gallon batches. I always do two at once because I find it more efficient on brew day. This was the FIRST time I've EVER used pelletized hops. I mention that in case I might have missed some basic rule in using them.
The pale ale came out great- in fact, we drank it in a week. Oh well. The stout had problems right off the bat- what I thought was a stuck fermentation turned out to be a leaking (though brand new) airlock, so fermentation signs weren't evident. I ending up transferring, re-pitching and then measuring after a week to find it done. Poop. I kegged it anyway, figuring that maybe it made it without contamination.
A few days after kegging, a weird flavor showed up. I would describe it as kind of sweet and not grossly rotten but...not good. I had it happen once before in a pale ale many years ago, and I attributed it to contamination, as it didn't go away after letting it sit cold in the keg and draining a bunch of it out (to try and get out settled yeast).
I left town for two weeks- two days before that I unplugged the keg fridge to move some things. I realized that I had forgotten to plug it back in after leaving. I was going to call my business partner (yes, I brew at work!) and then decided that I didn't really care, since my beer was ruined anyway, right?
I come back today- open the fridge, drain some beer out of the lines and taste it- wonderful! Ideas? I'm thinking aging let the yeast do some more work- but what was that work? why is the off flavor gone? Will chilling it back down bring the flavor back for some reason?
None of the "off flavor guides" I find online seem to match correctly- the closest cause I could find is Acetaldehyde, the symptoms of which are "rotten apples, green apple, freshly cut pumpkins"- don't really match. I'm hesitant to just say that must have been it, considering the problems I had with fermentation- this was the first time brewing in a new space, and also the first time I've had this much trouble fermenting. I suspected mold, but mold doesn't go away, so why does it taste good now? (Not even cold, tastes great...)