[scott]

I'm brewing my first Russian Imperial Stout.  It has been fermenting for 19 days, but it is not quite done yet.  It is at 1.042, and the recipe suggested a FG of 1.030 (using Wyeast 1084 or 1056).  The OG was 1.110.  I used WLP028 that I harvested from a previous batch, about half of the yeast, and saved the rest.  It was used the day after I harvested it.  Fermentation started in about 24 hours, at a controlled temp of 69°F, later raised to 71°F.  I used a blow off tube for the first time so I'm not sure how vigorous it was compared to previous batches.

Should I keep waiting?  Add some more yeast that I saved from the harvesting, now about 3 weeks old?  If so how much?  Thanks for any help.

[Jimmy K]

To really answer that we'd need to know - What and how much yeast did you pitch? What was the recipe? How are you measuring FG? 

1.042 is 61% attenuation - low, but possibly not surprising depending on the particulars. If the FG is stable over several days then it may be done - or stuck. If it's slowly dropping, then wait for sure.  Full attenuation from a 1.110 beer is definitely a challenge!

[redbeerman]

To really answer that we'd need to know - What and how much yeast did you pitch? What was the recipe? How are you measuring FG? 

1.042 is 61% attenuation - low, but possibly not surprising depending on the particulars. If the FG is stable over several days then it may be done - or stuck. If it's slowly dropping, then wait for sure.  Full attenuation from a 1.110 beer is definitely a challenge!

+1 what he said.

[dmtaylor]

Throw in some yeast energizer -- that often helps.

[AmandaK]

Throw in some yeast energizer -- that often helps.

This late in the game? He's 19 days in.

I've never used it, so I'm curious.

[scott]

I used WLP028 that I harvested from a previous batch (5 gallons), about half of the yeast.  White labs says that this yeast attenuates to 70-75%.  I don't have the recipe here with me at work, but it was Mik's RIS from "Beer Captured."

FG was measured using a hydrometer.

What is yeast energizer?  I added yeast nutrient at the end of the boil.

[Jimmy K]

Yeast energizer is (usually) diammonium phospate (DAP), it's kind of like meth for yeast. It can help keep a fermentation going, but it might be too late now. It's usually an ingredient in yeast nutrient too.
 
If it's in a bucket, you can gently stir up the yeast cake to resuspend the cells. That might help it ferment a little more.

[Joe Sr.]

I've got a tripel of similar OG that has been going slowly.  Last check it was getting close to what I expect as a FG, but we'll see this weekend if it has continued to drop.

I tend to get long slow ferments from really big beers (starting to think maybe I'm underpitching) but they do get there.

Do what you can to get the yeast back in suspension and raise the temp of the fermenter.  If that doesn't do anything for you, it may be finished.

I haven't seen any benefit from adding yeast energizer late in the fermentation.  Maybe there is some, but I've not noticed it.  I've also transferred other batches onto a fresh yeast cake with ambiguous results.

[blatz]

  I've also transferred other batches onto a fresh yeast cake with ambiguous results.

good to know - I've got a Triple IPA that's fermenting slow as molasses on the last 10-12 points and I have a regular IPA pounding away right now - I was thinking of dumping in some of the yeast from the regular one when its done, but if the success is limited, I guess I'll just be patient and hope. 

[Joe Sr.]

  I've also transferred other batches onto a fresh yeast cake with ambiguous results.

good to know - I've got a Triple IPA that's fermenting slow as molasses on the last 10-12 points and I have a regular IPA pounding away right now - I was thinking of dumping in some of the yeast from the regular one when its done, but if the success is limited, I guess I'll just be patient and hope.

I've done it a couple times and honestly can't say that it made the beer finish faster or lower.  They still went slowly, but the beers finished where I wanted them, so maybe that's an argument in favor?

I certainly don't think it hurt anything.

[denny]

Do nothing but be patient.  That's a big beer, and 19 days is no big deal for it.  Wait at least another week, maybe two, and then see where it's at.  I've screwed up more beer by trying to save them than I've actually saved.

[reverseapachemaster]

I agree with Denny. A beer that big can take some time.

[bluesman]

The apparent attenuation is dependent upon many things, like the yeast strain, yeast health, fermentation conditions, grist bill, etc... One thing that you need to consider is the grist bill. Can you post your recipe?

[erockrph]

How does it taste? I agree to the suggestions to give it more time, but go by what your palate tells you and not the hydrometer before deciding whether to do anything to the beer.

Even if it's done fermenting an RIS this big is going to take 6-12 months before it really starts to hit its prime, so there's no harm in letting it sit there for 4-6 weeks in primary. Patience is the most important ingredient in big brews.

[morticaixavier]

are you measuring with a hydrometer or refractometer?