The apple cider takes revenge. (aka: The Keg Incident)

About a year ago I brewed some cider.  I didn't give it much love or attention.  I left it sitting for months at a time without notice.  Long story short, it quickly became the red headed step child.

Sometime over summer, I decided to bottle it.  The yeast appeared to be dead, the bottles didn't carbonate, and the cider was too dry to be drinkable.  I blogged about this problem in August.  Thanks to a helpful suggestion from gregclimbs on the comments, I was able to save it by splitting it into two kegs, back sweetening with fresh cider, and force carbonating.  Before adding the fresh cider, I even attempted to "re-start" the fermentation in some mason jars, just to see if any yeast was still alive.  Nope, no activity in the mason jars, regardless of which sugars I tried.  After a week of testing, I felt pretty confident that the yeast wouldn't re-ferment.

I ended up bringing both kegs to my sister's wedding in September for everyone to try.  Unfortunately, the other beers I had available, and the Mango Melonade, were far more popular.  By the end of the wedding, I brought home both kegs of cider minus about 4 cups.

It sat in the garage for some time after the wedding.  The garage temperatures in September probably ranged from 95 degrees to 50 degrees, depending on the day.  The cider sat around like the red headed step child again.  Sometime last month I began to feel a bit bad about my 'orphaned brew' and shoved it into the fermenter/freezer.  I thought "hey, maybe I'll actually drink this stuff for fun".  Both kegs sat in there until last week when I decided to free up some space, and put one of the kegs out of it's misery.

I brought the single keg up to the kitchen, intending to dump it out, but completely forgot.  It sat there in the kitchen, the red headed step child yet-again.  Finally, the cider had had enough.  A couple of nights ago myself, my girlfriend, and my cat, were all startled to hear a very loud hissing sound.  We ran into the kitchen to see the keg sitting there making noise.

I was afraid it had over-pressurized and broke a seal somewhere.  But apparently the pressure relief valves are designed to automatically open before that happens.  After some time of listening to the cider hiss at me, it stopped.  I immediately walked over and pulled the relief valve to release more pressure.

I should point out that it usually only takes me a few seconds to evacuate gas from a corny keg at 40psi.  This time it took me about three minutes.  There was so much pressure built up that when I pulled the lid off of the keg, the cider was actually in a rolling boil, releasing co2.  I had somehow made a highly carbonated apple cider champagne.

The cider still smelled like fresh apples, and didn't show any signs of infection.  My theory is that all of the temperature changes finally woke up the yeast, and it's been slowly fermenting for some time now.  Anyone have an alternate theory, or had a similar experience?