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Brewing a Russian Imperial (E+G version of Austin Homebrew Supply's Jester King "Black Metal" clone) stout that seems to have stalled after transferring to secondary. I've corrected the most usual suspects by moving it to warmer room and swishing the carboy a little to bring the yeast back into suspension, neither of which has had more than a ~0.001 change. (Perhaps the yeast remaining after the secondary rack was cooled a little too much... autumn weather decided to make a late appearance.)

Question: Is the problem solved by infinite patience or another yeast vial?

Statistics:

  • Yeast: 2x WLP007 in 1L starter. BBE: 30 Jan 2014. Very vigorous fermentation for ~3.5 days.
  • OG @ pitch, 18 Oct.: 1.079 (calibrated refractometer with ATC)
  • SG @ secondary rack, 25 Oct.: 1.022 (corrected refractometer)
  • SG, 30 minutes ago: 1.021 (corrected refractometer)
  • Target FG: 1.013

Update: Patience be damned, I pitched a single vial of WLP007 (BBE: 20 Feb 14, no starter) to give the batch a last kick in the butt. Based on excellent responses, future best practice will include starters larger in quantity and gravity, as well as adding the forced fermentation test to troubleshooting procedures. Thank you for the responses.

Update 2: After pitching the third vial of WLP007 and waiting another week, there is no change in gravity. Considering the amount of attenuation (and the resources it's taking from future beers), I'm going to assume it's finished and let it age in the shed for the recipe-recommended six weeks in case of bottle bombs.

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I'm guessing this was an all grain recipe? And what was the package date or BBE date of the yeast? –  mdma Nov 5 '13 at 7:41
    
Please let us know in a few days if pitching the extra vial helped. –  mdma Nov 6 '13 at 8:36
1  
1.013 would taste pretty thin in an RIS. It's probably done, not stuck. –  baka Nov 6 '13 at 20:57

2 Answers 2

up vote 1 down vote accepted

The only way to know if it's stuck or it's finished is to do a forced fermentation test at 20°C/68°F on a small amount of the beer (say 1qt) with a fresh yeast.

WLP007 is a relatively good attenuator for an English strain, with the range given as 70-80%. The upper limit is in the optimum case, and you'll typically only reach this if there is adequate yeast, sufficient oxygen and nutrients at pitching, and a steady temperature.

Your current attenuation is 79-21/79 = 0.73 or 73%. Given that this is a high gravity brew, you should be sure to airate well, and pitch nutrients with the yeast. Also, maintaining a steady temperature (or even a slight increase as primary comes to a close) will also help keep the yeast active. If any of these pieces are missing, the yeast can drop out early and not reach the upper limits of attenuation.

Other factors to include are mash temp and grist - there may be lots of unfermentables in the wort if there is a significant portion of crystal or mash temps were high. Again, the forced fermentation test can tell you what the actual FG is for this wort.

Finally, even with two vials the 1 liter starter is not enough for this brew. Mr Malty recommends a 1.8l starter with completely fresh yeast, so I would go with a 2l starter or larger depending upon the age of the yeast.

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I wouldn't even consider 73% attenuation "stuck"... Especially in an Imperial Stout. –  baka Nov 6 '13 at 20:56
    
I agree - 73% may be the limit of attenuation on this brew, because of all the factors mentioned. –  mdma Nov 6 '13 at 21:13

The only way to know for certain whether or not fermentation has completed is to take gravity readings. If you notice that the gravity doesn't change after 3-4 days, and remains at a SG of 1.021, then you most likely have a stuck fermentation.

Unfortunately, pitching another vial of yeast is not likely to be as effective as you may need it to be. In order to "un-stick" your fermentation, you'll need to create a smaller batch of wort, pitch another vial of yeast, wait for it to reach "high-krausen", and then add that fermenting wort to your original stuck batch.

When you create this wort, ideally you will want to re-create your original recipe scaled down to about a ~1.5-2L batch so that you don't throw off your original recipe (grains, hops, and all). If you do not want to create a smaller recipe of your original brew (sometimes the waste and cost justifies the means), a simple yeast starter of a similar OG will work all the same. It wouldn't hurt in your case to try and find the darkest DME to use, as to not impact your Russian Imperial Stout's color too much. Simply match the OG of your stuck batch, pitch a vial/pack of yeast, aerate the snot out of it, add a teaspoon of yeast nutrient, and pour it in after 36-48 hours when you see a nice visible krausen on top. This will ensure that the yeast is healthy and ready to ferment out your beer the rest of the way.

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