[Hopspringseternal]

I'm brewing a Russian Imperial Stout, using Safale S-04, in a conical fermenter.  I've kept the temperature a steady 64 throughout.  Fermentation began after only five hours and airlock activity has continued for just over three weeks--although now it's down to about one bubble every 45-60 minutes.  The OG was 1.074. When I checked today it was only down to 1.023.  The estimated ABV is 8.5%, which would require a FG of 1.010 or less. Any reason not to assume that the yeast is still working?  If so, should I hold off on bottling until I see no airlock activity?

[BrewBama]

First off I am surprised S-04 took three weeks.

Ck SG again in two days and see if it matches today’s measurement. If it does it’s most likely finished. If it doesn’t it’s not finished yet.

Don’t trust airlock activity for fermentation progress. It could be done and just off gassing CO2. It could be still fermenting.


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[riceral]

Are you using a hydrometer or a refractometer to check FG?

Makes a difference.

[ravenwater]

That degree of attenuation does seem low for the yeast, if in fact you are at or near terminal gravity at 1.023
As noted, you should ideally be using a hydrometer to verify gravity once fermentation has started.
Definitely too soon to bottle before other data is collected and as stated by BrewBama you want to take a gravity reading on consecutive days, or a few days apart and compare before concluding that it's done fermenting.

[HopDen]

First off I am surprised S-04 took three weeks.

Ck SG again in two days and see if it matches today’s measurement. If it does it’s most likely finished. If it doesn’t it’s not finished yet.

Don’t trust airlock activity for fermentation progress. It could be done and just off gassing CO2. It could be still fermenting.


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I might also add to this that instead of using a traditional air lock, use a blow off tube that goes into a bucket of sanitizer.When fermentation is complete and if you have the means and your conical can be pressurized up to 15 psi, cap your FV with a PRV so you don't have any suck back when cold crashing. Assuming you can/do cold crash

[dmtaylor]

Here is your problem:

The estimated ABV is 8.5%, which would require a FG of 1.010 or less.

This is very unrealistic.  In my experience, S-04 has an average attenuation of about 78%, which with an OG of 1.074 would give an FG of 1.016 at best.

Warm it up for a few days to make sure it's done fermenting.  Then if it's done, it's done.

[Hopspringseternal]

Many thanks for all the great advice.  I am using a hydrometer to check gravity levels.  I'll check again in a couple of days and will hope to have more information about the status of the fermentation process.

[majorvices]

Here is your problem:

The estimated ABV is 8.5%, which would require a FG of 1.010 or less.

This is very unrealistic.  In my experience, S-04 has an average attenuation of about 78%, which with an OG of 1.074 would give an FG of 1.016 at best.

Warm it up for a few days to make sure it's done fermenting.  Then if it's done, it's done.

Yep. And I wouldn't even want a RIS that dry let alone 1.010

[Hopspringseternal]

I'm not sure what's going on with this Russian Imperial Stout...  As I originally posted, the OG was 1.074.  Two days ago the SG was 1.023.  This morning the SG reading was 1.029!  For what it's worth, I've continued to see steady but very slow airlock activity.  Is my hydrometer broken, or what's going on?

[dmtaylor]

I'm not sure what's going on with this Russian Imperial Stout...  As I originally posted, the OG was 1.074.  Two days ago the SG was 1.023.  This morning the SG reading was 1.029!  For what it's worth, I've continued to see steady but very slow airlock activity.  Is my hydrometer broken, or what's going on?

This is sounding more and more like measurement error.  Have you calibrated your hydrometer in plain water at about 60 F?  In any case, you might want to continue to measure a few more times until you can get a consistent number.

You also need to adjust readings for temperature.  The reading will vary a lot based on temperature.  There is a handy table at the bottom of this page (Table II):

https://www.morebeer.com/articles/Hydrometer_Calibration

Or you can use a calculator like this one:

https://www.brewersfriend.com/hydrometer-temp/

[Hopspringseternal]

Many thanks, DMTaylor, for these helpful resources.  I'll take a look at them!  I've also been wondering about the samples I've been taking.  Since I'm using a conical fermenter, I'm drawing the samples from the valve at the top of the cone (i.e., I'm not using the bottom valve, the one for removing trub).  Since the valve I'm using draws the sample from the bottom of the five gallons of brew I've wondered if it's simply thicker than the beer at the top.  I don't want to introduce oxygen, so I've resisted opening the fermenter and taking a sample from the top.  But maybe a sample from the top would have a lower SG...

[neuse]

I'm not sure what's going on with this Russian Imperial Stout...  As I originally posted, the OG was 1.074.  Two days ago the SG was 1.023.  This morning the SG reading was 1.029!  For what it's worth, I've continued to see steady but very slow airlock activity.  Is my hydrometer broken, or what's going on?

The paper inside the tube that has the SG scale on it can come loose. if it slides around, it could give different readings.

[denny]

I'm not sure what's going on with this Russian Imperial Stout...  As I originally posted, the OG was 1.074.  Two days ago the SG was 1.023.  This morning the SG reading was 1.029!  For what it's worth, I've continued to see steady but very slow airlock activity.  Is my hydrometer broken, or what's going on?

The paper inside the tube that has the SG scale on it can come loose. if it slides around, it could give different readings.

Ya know, that's what I've always heard, but in 23 years of brewing with hydrometer I've never had it happen.  Have any of you had personal experience with this?

[neuse]

I'm not sure what's going on with this Russian Imperial Stout...  As I originally posted, the OG was 1.074.  Two days ago the SG was 1.023.  This morning the SG reading was 1.029!  For what it's worth, I've continued to see steady but very slow airlock activity.  Is my hydrometer broken, or what's going on?

The paper inside the tube that has the SG scale on it can come loose. if it slides around, it could give different readings.

Ya know, that's what I've always heard, but in 23 years of brewing with hydrometer I've never had it happen.  Have any of you had personal experience with this?

No, I haven't, but I've read accounts of it happening on the forums. It's definitely something I'd check if I got some crazy readings.

[dmtaylor]

The paper inside the tube that has the SG scale on it can come loose. if it slides around, it could give different readings.

Ya know, that's what I've always heard, but in 23 years of brewing with hydrometer I've never had it happen.  Have any of you had personal experience with this?

YES.  I have been using the same hydrometer since 1999, never broke it.  Calibrating in plain water, it has in fact changed several times over the years, a point up or down here & there every few years.