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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.

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How much yeast did you pitch? Was it healthy? What's the expiration date on the yeast wrapper? I'd suspect you may have under pitched for that high of gravity. –  Scott Jun 4 '13 at 19:10
    
Also, what was the expected FG? –  Scott Jun 4 '13 at 19:17
    
Pitched one packet of S-33, it proofed like crazy almost immediately. I do not have the exp. date anymore. Recipe has FG at 1.026, but that was for OG of 1.096, which I overshot by 0.007. –  eli Jun 4 '13 at 19:38
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I don't think #3, #4, or #5 are anything to fear. The boil doesn't do anything to break down sugars; that happens in the mash. And I believe what occurs in the boil is actually NOT true "caramelization" (well maybe just a tiny bit right on the bottom of the pot), because you can't really caramelize at 212F. #5 was just that you never hit the hot break for all the wort, due to the massive gravity. That MIGHT cause clarity or head problems down the road, but shouldn't impact fermentability. –  Graham Jun 5 '13 at 12:14
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1 Answer

up vote 4 down vote accepted

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

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I aerated as vigorously as possible by hand. I think I will try to pitch more yeast. I'm not sure how the new yeast will survive without aeration, though...? –  eli Jun 4 '13 at 19:43
    
Some people report that just sprinkling yeast on won't do anything. Some even say that pitching 5% of another beer at high krausen (as described in the link) don't work. This guy seems to think that racking the wort onto another healthy cake will clear things right up every time. homebrewtalk.com/f13/psa-foolproof-stuck-ferment-fixer-72072 Any chance you have another batch ready to rack out of primary? –  Scott Jun 4 '13 at 20:07
    
Absolutely not, having more than one batch going at once is beyond my skills/equipment. What is so terrible about aeration at this point? –  eli Jun 4 '13 at 20:09
    
You definitely don't want to introduce any oxygen into the beer at this point now that fermentation is (near) complete. Doing so will impart some very distasteful flavors, reminiscent of chewing on a piece of cardboard. Check this link out: homebrewtalk.com/f39/… –  Scott Jun 4 '13 at 20:11
    
Do you have any DME around to make a yeast starter? In the event you do not have enough equipment to get a whole new batch going, your second best bet is to get a good yeast starter going, then add it at high krausen. –  Scott Jun 4 '13 at 20:13
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