These 2 works strike fear into the heart of any homebrewer, and most of us that have been brewing for a while have had it happen.
Your beer is bubbling along just fine and then all of a sudden it comes to a crashing halt before the final gravity is reached. The cause is usually technical – underpitching the yeast or low alcohol tolerance, for example. But this time the culprit was something large and clumsy – me.
You see, I'm anal about temperature control and use a chest freezer combined with an external thermostat to make sure my temps are spot on. The problem is that when I recently brewed a Dunkelweizen, my thermostat was in use by my new kegerator and the second thermostat hadn't arrived.
I had to make sure that my beer didn't get too warm when fermentation took off, so when the beer started to heat up I turned on the chest freezer without a thermostat and planned to cut it off once the temperature had been stabilized.
I fell asleep while watching a movie with my girlfriend and woke up at 3am in a panic. She thought the house was on fire. Worse – I nearly froze my beer.
The thermometer on the carboy read 32°F. Ice had started to form and the once vigorous bubbling in the airlock had ceased (because it was frozen). My yeast was in a deep sleep or possibly dead.
I was upset, but trying to see the silver lining I thought it was a good opportunity for a learning experience. I tried different techniques to see what would bring my beer back to life.
Things I tried to restart my fermentation
The Dunkeweizen was stuck at 1.020, which at 64% attenuation was well above where it should have finished. Here's what I tried:
Raised the temperature
Obviously the first thing I did was unplug the chest freezer and raise the temperature. I also swirled the carboy to get the yeast back into suspension. After a few days at 70°F I checked the gravity and it was still at 1.020.
Pitched new yeast
For an upcoming homebrew, I needed a 1.5L yeast starter. Instead, I made a 2L starter and when it was very active I pitched 500ml into the Dunkelweizen. A few days later I checked the gravity and it was still stuck at 1.020.
Racked onto yeast cake
This was my last resort. I kegged my American Wheat, then transferred the Dunkelweizen on the yeast cake. I wasn't a big fan of this option because I don't like adding unwashed yeast to a beer, but you know what they say about desperate times…
“Glug, glug, glug”
That's the sound of the airlock bubbling a day later. A krausen formed on top of the beer, and when I checked the gravity a few days later sure enough, it had dropped to 1.014 and then stayed there. It had 71% attenuation which was good enough for me.
So there you have it. A trial and error approach to fixing a stuck fermentation. Any advice on other things I should have tried? What have you had luck with?
Inside the Academy I teach the members how to avoid these situations in the first place by selecting the right yeast strain, pitching enough yeast, aerating, etc.
But none of these things matter when a big dummy falls asleep and freezes his yeast ; )