I recently brewed a batch and let it set in the carboy for 2 weeks. When it was transfered to the bottling bucket we noticed that it was a little carbonated already, which seemed odd. We ignored it and proceeded on to keg it like normal.
It measured a FG of about 1.002. Which was another red flag but it was not insanely lower than the projected 1.008.
The really odd part was when sugar was added to the keg for it to prime. Right when the sugar was poured into the beer it started overflowing the keg, and sort of foamed but mostly just gushed out, and was pretty neat/messy.
Any ideas what could have caused this effect?
We tasted the beer used to calculate the FG and it tasted good. No noticeable off flavors. One thought was that we did mash at 144, but I don't see how that could effect the carbonation.
Since I am writing this question a few days after the case and have had time to think I wondered if it could have been that the 3 piece was partly blocked from foam but not enough to push it off? I did not notice any hiss, or oddities from the 3 piece when I opened it, although I had "tasted" a few brews by that point.
EDIT: fixed FG to take temp into account.