I brewed a pumpkin ale and added extra fermentables. After primary and secondary was done, I went to bottle. While bottling I tried some and noticed the alcohol level was quite high. After two weeks in the bottles, I drank one and it was flat, I tried another and it was flat too. Is it possible that I stressed the yeast to the point that it wouldnt consume the priming sugar for carbonating? If so, how do I fix it?
So after looking up the recipe sheet for it off of Northern Brewer, I see that the estimated OG is 1.054. You say you added 3 lbs of DME on top of the recipe's ingredients. Assuming you hit the estimated OG of the recipe, we can calculate how much the DME added to it:
1 lbs of DME = 44 gravity points (0.044) per lbs of DME, per gallon of wort. You say you added 3 lbs, so that's:
If we head over to Mr Malty's yeast pitching calculator and plug in 1.080 OG at 5 gallons, it says that we need 2.8 vials of liquid yeast to ensure that it ferments fully. I assume you pitched one vial.
All that said, yes, your yeast is stressed really bad. I'd be willing to bet it didn't ferment all the way down to the expected FG, even with the addition of the 3 lbs of DME. At this point, since it is already in bottles, there is no easy solution to this. You have the following options:
Others may have more ideas on how to address this issue. Next time, I would consider pitching more yeast if I add more sugar than the original recipe calls for.
Although I could not tell you the science or specifics, this is certainly plausible. I left a (semi crazy) ale in secondary (well tertiary I suppose) for two years once, and when I bottled I supplemented the yeast after consulting with some local experts. The primary yeast was a flavorful belgian; since all I wanted was carbonation I went with something plain (1056 or S04 IIRC). Boiled up a beer "tea" with the yeast, pitched it 15m after the priming sugar, let it all sit for 30-60m before bottling, and it worked great!