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-   -   Issue with a Robust Porter's Attenuation (http://www.homebrewtalk.com/f36/issue-robust-porters-attenuation-388510/)

brighamj 02-09-2013 01:21 AM

Issue with a Robust Porter's Attenuation
 
Good evening, gentlemen.

I have recently brewed a first attempt at a robust porter, and the gravity seems a bit high after a few good? days of fermentation.. The recipe is as follows:

Yeast: Wyeast 1968 1600ml starter on stir plate for 24 hours before pitching

70% Maris Otter
11% German Munich
8% Hugh Baird Chocolate
6% Belgian Caramunich
3% Special B
2% Blackprinz

158 Strike
154 Mash for 60 minutes
169 Sparge

Post-Boil Gravity: 16.1 (1.066)
Current Gravity: 9.9 (1.036)

The gravity for the past week has been 1.036. I have even pitched a second batch of 1968 hoping to push the gravity a bit lower, but nothing.

Any ideas what's going on? I expected a much higher attenuation rate.

Thanks for the help.

Stauffbier 02-09-2013 01:26 AM

How long has it been fermenting and at what temp?

KeystoneHomebrew 02-09-2013 01:26 AM

Even with that yeast and mash temp, you're right. That's a high gravity reading. How long total has it been? Temp where the fermenter is?

Stauffbier 02-09-2013 01:34 AM

Since it has attenuated more than half way I would ramp the temp up to the high end of the yeasts range, which is 72F for 1968. I'd get it up to at least 70F, but do it slowly over a few days. If you already have it that warm, then I'd say just give it time.

brighamj 02-09-2013 01:45 AM

Thanks for the feedback so soon. I have it pegged on 68 and I pitched the yeast on Jan 29. What is that? 10 days?

stpug 02-09-2013 01:50 AM

Are these gravities by any chance obtained from a refractometer (16.4% brix and 9.2% brix)? If they are, and you haven't corrected your final gravity, then you're sitting at around 1.018 which would put your AA at 71.4% and that is right at the top end for that yeast.

KeystoneHomebrew 02-09-2013 01:51 AM

Sometimes highly flocculating yeast drop before the job is done. Give the fermenter a gentle rocking back and forth. As soon as your airlock has spit out most of it's reservoir, stop. That should help, as your temp is good. Just maybe the yeast is hanging at the bottom and not doing the job you (kinda) paid them money to do!

brighamj 02-09-2013 01:54 AM

Quote:

Originally Posted by stpug (Post 4882626)
Are these gravities by any chance obtained from a refractometer (16.4% brix and 9.2% brix)? If they are, and you haven't corrected your final gravity, then you're sitting at around 1.018 which would put your AA at 71.4% and that is right at the top end for that yeast.


They definitely are, and I think you are on the verge of teaching me something. I'm a bit embarrassed to ask this, but will you please explain the final gravity correction.

brighamj 02-09-2013 01:55 AM

Quote:

Originally Posted by KeystoneHomebrew (Post 4882629)
Sometimes highly flocculating yeast drop before the job is done. Give the fermenter a gentle rocking back and forth. As soon as your airlock has spit out most of it's reservoir, stop. That should help, as your temp is good. Just maybe the yeast is hanging at the bottom and not doing the job you (kinda) paid them money to do!


I tried to give them a bit of a swirl a few days ago, but I didn't want to do the stir for fear of oxygen and contaminates.

stpug 02-09-2013 01:57 AM

It's easier done than explained :D . This site gives all the nitty gritty details.

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


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