The mash that didn't kick, but then bucked

[Lblamboy]

I had an unexpected experience today with a 5th Generation UJSSM mash. On prior gens 2-4, I could hear the yeast kicking almost as soon as I added the sugar, and within an hour or two it was sizzling like bacon...This time that didn't happen, and by the 24 hour mark I was getting impatient...I had left the 4th gen sitting on the yeast a few weeks, and thought maybe I had exhausted it/killed it, and I had added warm setback before the water this time too, which I thought might have been a drastic PH drop that caused drama...and every gen from 2-4 I had also noticed the level of contents in the fermenter would rise a little - either because I was adding more new corn than I took off, or because I didn't get all the beer out, or both...

Anyway, I decided to throw some All-Grain yeast/mash slop from another container in just to see if that would do the trick overnight, thinking I probably had messed up the PH and would need to do something more this morning.

When I woke up, though, the mash had bucked, and the airlock was full of bubbling mash and there was mash all over the lid too. I was shocked to see that the level in the fermenter seemed even higher than I had left it?!?

Anyway, after cleaning it up, and stirring the mash extensively (it was absolutely sizzling...I love that sound!), I noticed the mash level had dropped nearly 3/4 of an inch! I don't know why the existing yeast didn't kick immediately like prior generations, and maybe it was the new slop I added that did the honors this time...but I'm left having to assume that the CO2 trapped in the mash was so voluminous that it added a significant amount of volume to the whole fermenter...and that was at least part of the reason it reached the airlock!?!

Fortunately it wasn't "that" messy to clean, but I'm still just amazed by that volume change...never saw that one coming!