I brewed a session stout about 4 months ago, and left it in the fermentor for two weeks. The FG was 1.012 one week in, and I checked every few days until 2 weeks in, and the FG remained at 1.012. I added enough corn sugar to add 2.0 volumes of CO2, and spent 120 seconds stirring it slowly into the bottling bucket. The bottles have been conditioning at room temperature during the winter.
I pulled out a bottle the other night and found it to be too carbonated. I poured some into a test jar and waited 3 days before measuring its gravity to ensure that carbonation wouldn't alter the results.
The final gravity of this sample was 1.010.
I'm straining to see the cause of this. The FG remained at 1.012 for a full week before bottling, the fermentor was under perfect temperature control, and I used an adequate yeast starter, so it is hard to think that the yeast did not attenuate fully. I spent 2 minutes stirring in the corn sugar, so it is hard to think that the sugar was not evenly distributed.
What could be the cause of this?
9 # Marris Otter 1 # Roasted Barley OG: 1.047 Wyeast 1028, Yeast Starter 1.5L 1.035 East Kent Holdings 1.75oz 4.5% AA Fermented at 65*F in a chest freezer, raised to 70*F after four days Time in fermentor before bottling: 2 weeks Final gravity prior to bottling: 1.012 Final gravity 3 months and 2 weeks after bottling: 1.010