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So, a little under a week ago, I brewed a goodly sized stout (1.069 OG) and when I mashed it I ended up missing my mash temp by about 4 degrees. (I was aiming for 158 and ended up with about 162-163.) I kept stirring with the lid of my cooler open to get the temperature down to 158, but this took about 10-15 minutes. I then mashed for a full 60 minutes and ended up hitting my gravity right on the nose.

I pitched a 1L starter of US-05 into it, and had a quick, active fermentation for 4 days (at about 62-66 degree range), and now the airlock is not moving anymore. This is when I usually start taking my gravity readings, and today I took one but it's only down to 1.030, but I'm expecting to get down to about 1.019.

Did mashing at such a high temperature "break" the extraction and I'm down as far as it will go? Seems strange that it did since I hit my numbers...

My plan is to RDWHAHB and let it sit for another week or two, but I'm just curious as to what might be going on here.

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This sounds about right. A bigger brew doesn't always hit FG within 4 days. I'm sure you'll be fine leaving it another week.

The mash temperature is high, so this could have produced a larger than normal amount of non-fermentables, leading to a high FG. But, I wouldn't make that conclusion until after at least another week has passed, with an ambient temp of 66-68F/17-18C.

Some points to keep in mind:

  • no airlock activity does not always mean no fermentation, so rouse the yeast and leave it a week and then check the gravity again. If the gravity's not moved, then you've hit final gravity for now.
  • if the FG is still high, then determine if it's the brew or the yeast that's causing the terminal gravity to be reached by doing a forced ferment test. Take two samples, and in one sample, add a pinch of beano or dry beer enzyme from your LHBS. Pitch fresh yeast to both, and ferment both in the same location, warm (70F/20C) with occasional shaking. After 4 days take a gravity reading.

    1. If the one without beano reaches an acceptable FG, then it's the yeast that has given out, possibly due to temperature. Ferment warmer or pitch some fresh actively fermenting yeast.
    2. If the one with beano reaches an acceptable FG while the one without is still high, then the mash is causing the high FG. You can either choose to live with the high FG, or add a touch of beano to help bring the FG down.
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Did you mean to suggest adding yeast to one of the samples in your proposed experiment? –  Tobias Patton May 9 '12 at 14:03
    
Thanks for the answer. I like the approach of relaxing and not worrying, but I'm just getting back into brewing after 5 years, and it's really hard to be patient when there's no backlog! :) –  Ben Belchak May 9 '12 at 14:49
    
@TobiasPatton, I've edited the answer - some details lost after reworking the text. I hope it's clear now. Thanks for noting. –  mdma May 9 '12 at 15:58
    
You're proposing a forced ferment test with the finished beer? –  brewchez May 9 '12 at 23:22
    
forced ferment on some samples. It's not known if the beer is finished or not, the forced ferment will find out the actual final gravity given optimial conditions for fermentation. I also add in some enzymes to see if they help reduce the gravity if the high fg is from non fermentables. –  mdma May 9 '12 at 23:32
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Despite the high mash I'd expect it to go a little lower. If you didn't pitch enough yeast at the outset or properly aerate the wort its likely stalled due to poor yeast health.

Another reality could be early transfer. Removing the beer from the yeast cake too soon can stall a ferment. Two weeks on the cake is a minimum.

I'd warm it up to 70F. While that is happening get a 0.5L of wort going (50g DME and 500ml water). Pitch some fresh yeast in there in the morning and shake it occasionally. When you notices a decent krausen forming in the starter, pitch the whole thing right in the beer. Keep it warm for another 7-10 days. Then recheck the gravity.

Might not be the best tasting beer, but it won't be bad. This is the best way to restart a ferment. But it sounds like you are being a little premature with worrying only 4 days in. I'd warm it up to 70F for the next 10-14 days. The initial 4 days is where the low temp is critical for a clean fermentation profile. Its OK to warm it up now to help dry it out.

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