Is this a bottle bomb waiting to happen?

Question

Planning a strong & sweet Belgian style ale, I expected OG to be as high as 1.096. Because of my extremely amateur setup, I used two pots instead of one big one for the boil (between them both I managed to fit in only 2 gallons of wort, out of a 5 gallon batch). OG ended up a whopping 1.103!!! I believe this is due to high evaporation (and I suspect that the specialty grains soaked a large amount of water up).

OK so now fermentation. It took less than a week to drop to 1.040, but we're at 2.5 weeks now and it doesn't seem to be budging from 1.038. Even after swishing the carboy around a few days ago.

I'm perfectly happy with the taste and sweetness of this beer. But if I bottle at FG 1.038, is this a bottle bomb waiting to happen? Or does one of the following scenarios sufficiently explain the phenomenon:

1. The yeast (S-33) has reached its alcohol tolerance, and cannot ferment the brew further. (The beer is at either 8.5% or 9.5% ABV, depending on what formula you use.)
2. Not enough yeast pitched (1 packet, rehydrated & proofed, and lots of hand-aeration).
3. Small boil volume has reduced efficacy of process to break down sugars, leaving unfermentable sweetener in the mix.
4. Small boil volume has increased caramelization of sugars, rendering them unfermentable. (Seems likely due to flavor.)
5. Large amounts of Mystery Proteins in the wort (evidenced by foam that never stopped appearing in one of the pots).
6. Divine intervention / household hobgoblin / angry ghosts of Belgian beer crafters.

Fermentation temp is not an issue. It hasn't gone below 25C/77F during the entire fermentation.

I'd appreciate any insight. Especially "just bottle it and it will be fine". I'm hoping for that one.

Answer 1

I'd be willing to bet that the high FG was due to insufficient yeast pitching. By itself, most yeast can handle up to 13% ABV, so it isn't the intolerance of your alcohol level. I would recommend doing a yeast starter for brews this high in gravity (a little late now obviously). In your situation, I would consider pitching another packet of yeast (see the link below on how to properly pitch more yeast) if the FG is supposed to be substantially lower than 1.038 (1.01#). For the purpose of homebrewing, it's generally safer to overpitch yeast than to underpitch.

Aside from the possibility of underpitching, did you aerate the wort before pitching your yeast and letting it ferment? If there isn't enough oxygen in the wort, it will limit the yeast's ability to reproduce, therefor not fermenting fully. Something that high in gravity definitely demands a lot of aeration, more so than what a gravity reading of half that would require. If you did not properly aerate the wort, then pitching more yeast will not help.

As far as bottling goes, unfortunately I'm uncertain as to whether or not the yeast will wake up after being racked to bottles, and continue to ferment the remaining sugars. If it is a matter of underpitching, I would imagine this could be a concern.

Here's a good write-up on how to handle what people call a "stuck fermentation": http://www.brewboard.com/index.php?showtopic=89541