Stuck fermentation head scratcher

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etxflyer

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I’ve had an ongoing problem with what I suppose is stuck fermentation that I’m hoping someone here could help me figure out. I’ve researched extensively to try to solve the problem, but I’ll skip all of that just to say that my process I’m about to describe is the product of that research and me trying to solve this issue.

I brew all grain with typically an hour boil on a grainfather setup. Achieved 1.059 OG (should’ve been 1.049 according to recipe). The last batch was a Kolsch but this has been happening with Pilsners and lagers. Use fermcap and whirfloc and transfer to a corny keg (with floating dip tube) using a wort aerator from the top of the keg to get plenty of O2. Pitch a yeast starter that has been on stir plate for 24 hours (imperial dieter this batch) and ferment in a temperature controlled chamber at 65 degrees using a sounding valve at about 12 psi. Reading the SG with a refractometer that I calibrated with distilled water.

Here’s the issue - everything seems to go fine but at about 10 days gravity stalls at 1.030. I’m supposed to be at 1.009 according to recipe. I let it go another week and I’m still at 1.030. I’ve tried shaking the keg and that doesn’t seem to do anything. In the past, I’ve just said “oh well” and put in the kegerator and it’s been great beer, but I’d really like to try to nail down where in my process I’m screwing up. Any suggestions or insights would be appreciated.

Cheers!
 
This is likely your problem. "Reading the SG with a refractometer"

Refractometers are great for getting the OG but the alcohol in the finished beer makes them read high. Use a hydrometer on your finished beer and see if that fixes the problem.

The recipe you used probably assumes a 70% brewhouse efficiency and you are getting better than that. If you use brewing software you can make some changes to the expected efficiency to compensate.
 
everything seems to go fine but at about 10 days gravity stalls at 1.030. I’m supposed to be at 1.009 according to recipe
Since your OG is higher than the recipe prediction, your FG will also be higher. 1.049 to 1.009 is just under 82% apparent attenuation, which in turn would be a FG of about 1.011 with an OG of 1.059. Assuming that you are trying to read SG from your refractometer instead of reading Brix and converting with the appropriate correction factors, I'd guess that you're FG is really something like 1.014 which IMO is close enough to RDWHAHB.
 
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Yall are genius! Can’t believe i got such a quick response and that I was fine all along! I certainly learned something today - for some reason I was under the impression that the refractometer was more accurate. Into the kegerator she goes!!!! 🍻🍻🍻
 
under the impression that the refractometer was more accurate
Glad this has a happy ending! I've largely given up on using my refractometer, instead losing the 150ml of beer whenever I need to measure gravity. For me, it's been inconsistent, and correction formulas won't fix that. Others have chosen to use it only to measure differences near end of fermentation, to ensure gravity is no longer dropping. Some, of course, swear by their refractometers and correction formulae. It would be way cool to get reliable data from only a drop or three of wort/beer...<sigh>
 
Glad this has a happy ending! I've largely given up on using my refractometer, instead losing the 150ml of beer whenever I need to measure gravity. For me, it's been inconsistent, and correction formulas won't fix that. Others have chosen to use it only to measure differences near end of fermentation, to ensure gravity is no longer dropping. Some, of course, swear by their refractometers and correction formulae. It would be way cool to get reliable data from only a drop or three of wort/beer...<sigh>
Been very happy with my $13 amazon refractometer, it's been within a point or two of every hydrometer measurement I've done -- it's certainly within the tolerance of my aging eyeballs.

But one thing you might try, is after taking your hydrometer sample, leave it in the tube and cover it up with some cling wrap, that way you can watch the gravity change in real-time! BrewnWKopperKat has a nice picture here.
 
But one thing you might try, is after taking your hydrometer sample, leave it in the tube and cover it up with some cling wrap, that way you can watch the gravity change in real-time! BrewnWKopperKat has a nice picture here.

For this approach, I remove the sample about a day after the yeast has been pitched. The wort in the sample tube will ferment at the same rate as the fermenter. When the krausen drops, it's safe to start taking FG measurements.

Taking SG measurements while it's fermenting may cause the fermentation in the sample tube to stall (probably because cleaning away the krausen removes additional top fermenting yeast).
 
Seriously, you can use a refractometer, and it should be accurate within a couple gravity points, if you use these conversion calculators. Use Sean Terrill when you expect gravity below 1.014, and use Brewer's Friend when you expect gravity above 1.014. Links:

http://seanterrill.com/2012/01/06/refractometer-calculator/

https://www.brewersfriend.com/refractometer-calculator/

Personally I also recommend a Wort Correction Factor of 1.00, which is the default on BF but not on Terrill, so beware. If you know your own WCF then of course remember to use it. BF teaches you how to determine your WCF which is different for different people and different refractometers, but should hover somewhere between about 0.98 to 1.05. Mine is actually 0.995, very very close to 1.00. This was determined through analysis of many dozens of my batches, but you can get a good feel for it within the first 5 or 6 batches, if you compare every reading against a hydrometer for a little while. All optional. Otherwise just use 1.00 and call it "close enough".

All of this was determined beyond much doubt by yours truly after WAY too many hours of analysis and pondering. Believe me or not, but maybe try again with this guidance and see how close your results come comparing hydrometer to refractometer calc conversions.
 
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Well, I guess my problem was it never even occurred to me that the refractometer would be the problem so I never searched that direction and that’s the reason I spelled my process out. I just had it in my head that it was a stuck fermentation problem. I’m just happy to have learned something else! That’s a great idea about watching the fermentation/SG in real time, ima give that a try! Thanks again for all the great advice everyone!
 
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