Stuck fermentation or too efficient a mash

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mhochman

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My recent all grain batch of AHS Fat Tire Ale clone appears to be stuck at about 1.019/1.020 (after three weeks, gr hasn't moved in two weeks). Expected fg is 1.011. Apparrent attenuation is 61% (instead of 75%). I'm usually ok with my fg being close, but this seems a bit farther than I'm comfortable with. I've started searching and reading up on how to get a stuck fermentation going again, but then I had a thought. I checked my numbers, and it appears that my expected OG was 1.047, mine was 1.050. I also noticed that expected efficiency of 75%, but my efficiency apparently was 88.5%. So now I'm wondering if I just converted to much starch and the yeast just can't handle the excess. Do I need to try to get the fermentation going again, or should I just resign myself to a slightly sweeter version of the beer. FWIW, samples taste great.

Some other info:
-I used Notty
-My readings have been adjusted for temp
-Beer is presently sitting at about 66 deg F

Thanks all
 
What was your mash temp? This has a big effect. Its possible, maybe even likely in my opinion, that the yeast are done.
 
I agree. It has most likely reached terminal gravity. If you want it more dry, mash at a lower temp next time like 148-150.
 
gstrawn said:
What was your mash temp? This has a big effect. Its possible, maybe even likely in my opinion, that the yeast are done.

152. Stayed at that temp for the full 60 minutes.

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It's probably done, but you could try a warmer spot (like 70 degrees) to see if you can knock off a few more points.

Or you could just bottle it and it'll be great.
 
TyTanium said:
It's probably done, but you could try a warmer spot (like 70 degrees) to see if you can knock off a few more points.

Or you could just bottle it and it'll be great.

Ok, I moved it to a warmer spot. Naturally, the move shook loose a little of the yeast cake, so maybe I'll get a little action. If nothing is different Sunday, I'll rack to the keg. If I notice a change I'll let it sit tight.

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Good plan. Some even suggest giving it a GENTLE swirl to resuspend some yeast, but your moving it is probably sufficient enough. If it drops a few points, great. If not, you still will have delicious beer. :)
 
I checked my numbers, and it appears that my expected OG was 1.047, mine was 1.050. I also noticed that expected efficiency of 75%, but my efficiency apparently was 88.5%. So now I'm wondering if I just converted to much starch and the yeast just can't handle the excess.

where'd you get 88.5%? 50 vs 47 is only 79% efficiency

not sure what you mean by converted too much of the starch, it should always be all converted. and no, theres no yeast that couldn't handle that small of an excess anyway, esp notty. you may want to check your themometer, cuz notty shoulda tore thru that if you really mashed at 152F. hopefully the agitation and warmer temps get you the rest of the way tho
 
where'd you get 88.5%? 50 vs 47 is only 79% efficiency

not sure what you mean by converted too much of the starch, it should always be all converted. and no, theres no yeast that couldn't handle that small of an excess anyway, esp notty. you may want to check your themometer, cuz notty shoulda tore thru that if you really mashed at 152F. hopefully the agitation and warmer temps get you the rest of the way tho

That's the number my software gave me, based on total grains and my pre-boil gravity reading. By converting too much I meant that isn't there always some starch that doesn't end up getting converted? That's why we don't all get 100% brewhouse efficiency, right? Or am I confused? I was thinking I converted more than typically gets converted for this amount of grain following the instructions I had.
 
That's the number my software gave me, based on total grains and my pre-boil gravity reading. By converting too much I meant that isn't there always some starch that doesn't end up getting converted? That's why we don't all get 100% brewhouse efficiency, right? Or am I confused? I was thinking I converted more than typically gets converted for this amount of grain following the instructions I had.

All the efficiency is measuring is how much of the potential sugar you have released from the barley. The missing percentage is what you havent rinsed out of the mash. We don't get 100% because it is difficult to extract that last little bit without using mechanical means.
 
foltster said:
All the efficiency is measuring is how much of the potential sugar you have released from the barley. The missing percentage is what you havent rinsed out of the mash. We don't get 100% because it is difficult to extract that last little bit without using mechanical means.

Got it. So just to change my wording: I'm wondering if I rinsed out more converted sugar than expected, raising the expected gravities all around.

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yes, but going 3 pts higher in OG doesnt equate to 9 pts higher in fg. it should only raise it about 1pt

from what you've told us, nothing sounds wrong with what you did so im a bit confused why you have a stuck ferment. give the warmer temps and agitation a shot and hopefully it does the trick. if it doesn't, there are some more ways to try to restart a fermentation, or you can just let it be if you feel safe bottling it since it tastes good as is.
 
dcp27 said:
yes, but going 3 pts higher in OG doesnt equate to 9 pts higher in fg. it should only raise it about 1pt

from what you've told us, nothing sounds wrong with what you did so im a bit confused why you have a stuck ferment. give the warmer temps and agitation a shot and hopefully it does the trick. if it doesn't, there are some more ways to try to restart a fermentation, or you can just let it be if you feel safe bottling it since it tastes good as is.

Sitting tight. Temp already sitting about 68. Hoping to see it around 70.

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I think you are going down the right path here. If you raise the temp and see no significant change in FG then the yeast has likely consumed all the sugar it is going to.
 
Got it. So just to change my wording: I'm wondering if I rinsed out more converted sugar than expected, raising the expected gravities all around.

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No, you WANT to rinse out all of the sugars you can. You didn't do too badly, getting 79%- a typical homebrew efficiency.

I really feel that your thermometer is off. No way a 1.050ish OG with nottingham would finish at 1.020 unless you mashed at 155/156. But if your thermometer is even 2 degrees inaccurate, that could easily be what happened! I'd double check that thermometer calibration before you brew again.
 
Yooper said:
I really feel that your thermometer is off. No way a 1.050ish OG with nottingham would finish at 1.020 unless you mashed at 155/156. But if your thermometer is even 2 degrees inaccurate, that could easily be what happened! I'd double check that thermometer calibration before you brew again.


Makes perfect sense. I was looming to get a digital thermometer to leave in the mash, so maybe I'll do that now. I'm glad I asked, because in my mind I had only considered a fermentation issue and I'm too knew at AG to know what to think about there. Thanks again.

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Makes perfect sense. I was looming to get a digital thermometer to leave in the mash, so maybe I'll do that now. I'm glad I asked, because in my mind I had only considered a fermentation issue and I'm too knew at AG to know what to think about there. Thanks again.

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There a lots of factors in attenuation- yeast strain, mash temperature, ingredients, yeast health and oxygenation, temperature, etc.

But in this case, while there is some crystal and Munich malt in your grainbill (assuming, since you said Fat Tire clone), there aren't going to be many unfermentables unless you mashed at a high temperature.

Since you had good conversion apparently and good lautering efficiency, used a well-attenating ale yeast, had fermentable ingredients, etc, only a couple of things could be the cause. One would be poor yeast health- like under aeration of the wort- but more likely it is a too-high mash temperature leaving too many unfermentable long-chained sugars.
 
No movement after three days. I'm kegging it tonight. Amazing beer will have to now just be really great beer. Learned a lot on this thread, though. Thanks all.

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I really feel that your thermometer is off. No way a 1.050ish OG with nottingham would finish at 1.020 unless you mashed at 155/156. But if your thermometer is even 2 degrees inaccurate, that could easily be what happened! I'd double check that thermometer calibration before you brew again.

Sorry to wake this old thread, but today I calibrated the thermometer I had used on that brew day with two others that were consistent with each other. Turns out my "old" thermometer was almost 10 degrees off! Thank you so much for helping me to realize that could be the issue. I had brewed again between that batch and today's and the batch in between was definitely off as well.

Appreciate the help. :mug:
 
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