Brewed a cream ale Sunday - nothing exciting: 5 gallon batch (in an 8 gallon fermenter), OG 1.047, 85% american 2 row, 15% flaked corn, wyeast 1056 smack pack, no starter.
It was fermenting fine Monday morning and evening. I got home tonight and the fermenter lid had swelled like a pregnant belly. Krausen through the airlock (plugging it completely).....I think if I had come home an hour later it could have been messy.
I've heard all the arguments for blow off tubes before, but this is the first time I have ever needed one in 40+ batches. No idea what's going on, as I've brewed wheats, hefes, and high gravity beers before with no problem.
The only things I can think of are that I got a smack pack with a really high yeast cell count, or it had something to do with the corn. I also aerated a little more than normal.....
Anyway, I'm just glad I didn't have to clean up an explosion!