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:
- 3 lbs of DME * 0.044 SG for each lbs = 0.132 SG in one gallon of wort
- 0.132 SG / 5 gallons of wort = 0.0264 additional SG after accounting for 5 gallons of dilution
- 1.054 estimated OG from the recipe + 0.0264 ~= 1.080 OG of your wort after accounting for the DME
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:
Try and pitch a small pinch of dry yeast into each bottle and re-cap. Problem with this is that you will likely need to go in every day or two and un-cap them, as it is likely the yeast addition will over-carbonate and cause geysers/bottle bombs if left to build up enough pressure. I would highly advise against this.
Risk oxidation by gently pouring them into your bottling bucket, pitching more yeast through the use of a 1-2L 1.040 SG starter at high krausen, hoping to kick start fermentation again enough to clean up the rest of the sugars, and then attempt to re-bottle after a couple of days, more advisable than the last
Enjoy it flat. Which off-flavor would you like more, wet cardboard, or flat, pick your poison.
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!