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.

 

How long has it been fermenting and at what temp?

 

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?

 

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.

 

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?

 

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.

 

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!

 

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.

 

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.

 

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

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

 

*Mindblown* (I think)

So this refractometer has been lying to me this whole time?

 

Alright. So after pumping from boil kettle through chiller and into fermenter, I always take an accurate hydrometer reading. However, as fermentation occurs, I sample with a 5ml glass pipette and test the gravity with a VeeGee refractometer. Correct me, if I'm wrong, but I should be using my initial reading against the refractometer reading adjusted for the factor given on sean terrill's site? Sorry for probably not going through the fine print, but it is Friday and I have been drinking beer which may in fact be higher in ABV than I thought. Ha!

 

You definitely don't need to stir once you have re-pitched more yeast like you did.

It sounds like stpug has pointed you in the right direction with the refractometer info...

 

Going through the small print of that point in the morning is definitely on the agenda. Thanks to all of you who helped out. I love it around here!

 

Just to provide an update in case it helps the next brewer...

I racked the porter over to a corny this morning, took a hydrometer reading, and it was right on 1.0215. Thanks guys.