Mystery Fermentation

TroubleShooting

Bob Hines — Chapman, Kansas asks,

I brewed A Founder’s Breakfast Stout clone from BYO, added some extra grain and my OG was 1.090. It was my first beer with coffee, chocolate and cocoa nibs. I pitched half of the batch with some S-05 yeast harvested from a recent batch of porter and pitched the other half with fresh S-04 as an experiment. I brewed the stout on Sunday, and on Monday when I got home there was only a bit of foam (it was oily looking) on top of the beer but no real kräusen and there were no bubbles coming out unless I shook the carboy. After about three days of shaking, I couldn’t get any more bubbles to come out from shaking. Thinking I did something to kill my yeast, I added extra yeast (S-05 to both). I kept watching and saw no signs of fermentation. Thinking that maybe the chocolate or coffee did something to prevent the yeast from fermenting, I gave up on the beer but decided to hold off on dumping it. Six weeks after brewing the gravity reading was 1.030. How and when did this ferment? Did an infection consume the sugar?