Banana Aroma developed in keg?

Mashing
1

I just brewed a Dry Irish Stout and put it in a keg to dispense by cask (corny keg, Valterra rocket hand pump, etc). When I sampled before I kegged, it tasted pretty good. It was to style and I didn’t notice any off flavors. When I kegged, I used pure demerara sugar in place of sucrose; something I’ve never done. After sitting for a week or so to carb up, I’ve noticed a pretty distinct banana aroma when I dispense the beer. It’s been like this for about 10 days or so. I should mention that I fermented around 64-66 with Wyeast 1084.

I’m wondering if the secondary fermentation responsible for carbing caused this, and if it’ll eventually clean up. Any ideas? I’ve never experienced this aroma before, and the beer just isn’t very enjoyable with that first smell makes it seem like someone shoved a banana in my nose. It dissipates some, but doesn’t disappear. Weird.

2

Odd. Do you have another empty keg that you can fill with cleaner? Maybe purge your keg lines with cleaner, fill the keg with water and run that through, then fill it with sanitizer and run that through.

After all that, get the stout back on line and maybe drop your serving temps a little, say around 40-45*

Might work.

3

My first thought was that it sounds like you picked up a wild yeast infection somewhere. I wouldn’t think the mini-fermentation caused by adding a small amount of priming sugar would create such an offensive off-flavor or that it would still be there after >10 days.