Author Topic: FG questions  (Read 800 times)

Offline Brewmeisters

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FG questions
« on: December 02, 2017, 11:03:22 AM »
we bottled our RIS tonight.
FG was 1.030.
ABV is 5.3%
Should have been 7.6-8.3%
We pitched the yeast at 79 degrees, fermentation stopped at 4 days.
Ambient temperature was 60-61 degrees.
We kept it in The fermenter for the next 2 weeks.
So, help me understand what happened?
Why didn’t we reach our goals?
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Offline BrewBama

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Re: FG questions
« Reply #1 on: December 02, 2017, 12:59:39 PM »
What yeast strain?  What does the spec sheet say about expected attenuation? 

Some yeast strains rush thru fermentation and have to be encouraged to continue their job. For example the English will recirculate the fermenting wort thru a fish tail to keep their strains active.

Also, some strains do not process malto-triose as well as others leaving the beer with a higher FG and fuller body.


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Offline pete b

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Re: FG questions
« Reply #2 on: December 02, 2017, 01:22:24 PM »
Are you the one that pitched yeast in the high 70s. I'm actually concerned that you have a stuck fermentation here because  I think you might have pitched at a high temp but the ambient was much lower as I recall. This could result in too much alcohol too fast coupled with a big temperature drop compromising the yeast.
I am worried about bottle bombs. I really think you should sacrifice a bottle and do a fast ferment test to make sure it's done, taking into account priming sugar. If there is a significant drop in gravity and the yeast was only dormant and not dead you could have a dangerous problem.
I think the problem here was the high temp pitch. You should bring it down closer to fermentation temperature before pitching. If you pitch in the high seventies and store in the sixties ambient the yeast activity will initially heat up the fermenter into the mid eighties, ferment most of the sugar but not all then as the activity lessens it will fall to ambient. For big beers it is actually better to warm it up a little as Krausen ends to help finish.
It would also be good to see your grain bill.
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Offline jeffy

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Re: FG questions
« Reply #3 on: December 02, 2017, 01:34:20 PM »
Did you use a refractometer to measure the final gravity?  If so, you need to convert the measurement to make up for the alcohol. 
If you used a hydrometer, then 1.030 is pretty sweet and full.  Either you didn’t let it ferment long enough or the yeast got tired and gave up.
What as the O.G.?
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Offline dmtaylor

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Re: FG questions
« Reply #4 on: December 02, 2017, 01:54:21 PM »
Need the complete recipe including mash temp and time, and yeast strain and starter details, and the OG.
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Offline BrewnWKopperKat

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Re: FG questions
« Reply #5 on: December 02, 2017, 02:02:55 PM »
So, help me understand what happened?
Why didn’t we reach our goals?

If the current topic is a follow-up to this https://www.homebrewersassociation.org/forum/index.php?topic=30616, then the concerns about incomplete fermentation and possible bottle bombs would be worth investigating.

Doing this

Need the complete recipe including mash temp and time, and yeast strain and starter details, and the OG.

will definitely help answer your questions.


Offline dmtaylor

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Re: FG questions
« Reply #6 on: December 02, 2017, 02:30:37 PM »
If the current topic is a follow-up to this https://www.homebrewersassociation.org/forum/index.php?topic=30616, then the concerns about incomplete fermentation and possible bottle bombs would be worth investigating.

Based on that other thread, it looks like they waited a couple weeks and used S-04, with OG=1.070.  Finishing at 1.030 does not seem right.  Now I have to wonder if they really are using a refractometer for FG without alcohol correction a la Terrill.  That, or the SG measurements are not correct, perhaps not corrected for temperature.

Did you measure OG at 79 F or higher?  If so, your OG measurement was very likely incorrect, and was actually closer to 1.080 or higher depending on temp.  Do you remember how hot the wort was when you measured OG??
« Last Edit: December 02, 2017, 02:32:52 PM by dmtaylor »
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Offline BrewBama

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Re: FG questions
« Reply #7 on: December 02, 2017, 03:15:24 PM »
S-04 usually gets ~75% for me so it should be finished at ~ 1.017 so something is definitely going on.


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Offline Brewmeisters

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Re: FG questions
« Reply #8 on: December 03, 2017, 09:09:19 AM »
It is a Brewers Best Russian Imperial Stout.
Yes, we pitched the yeast at 78 degrees.
Yeast was Sarfale S-04.
OG was 1.070
FG is 1.030 using a hydrometer.
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Offline BrewnWKopperKat

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Re: FG questions
« Reply #9 on: December 03, 2017, 01:22:43 PM »
It is a Brewers Best Russian Imperial Stout.
Yes, we pitched the yeast at 78 degrees.
Yeast was Sarfale S-04.
OG was 1.070
FG is 1.030 using a hydrometer.
Are these the kit instructions: http://www.brewersbestkits.com/assets/1046-2016-russian-imperial-stout-recipe.pdf ?

Offline pete b

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Re: FG questions
« Reply #10 on: December 03, 2017, 01:36:16 PM »
I believe the most likely thing is that the pitch temperature vs the ambient temperature plus a fairly high OG resulted in a stalled fermentation.
From the other thread yeast was pitched at 79F and fermenter kept at 60F.
I think that either the yeast is dead and the beer will be flat and under attenuated or some yeast will perk up from the bottling process and there will be bottle bombs after a time.
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Offline a10t2

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Re: FG questions
« Reply #11 on: December 03, 2017, 04:37:10 PM »
Are these the kit instructions: http://www.brewersbestkits.com/assets/1046-2016-russian-imperial-stout-recipe.pdf ?

Given that it's all dark extract (and assuming the 1.070 sample wasn't homogenous) 62% ADF might not be out of the question.

OTOH, the instructions say to pitch one packet of unrehydrated yeast, so the pitching rate was extremely low - AND the ferment started warm and then crashed, so I wouldn't rule out a stalled fermentation either.
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Offline BrewnWKopperKat

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Re: FG questions
« Reply #12 on: December 03, 2017, 06:20:02 PM »
So given this

It is a Brewers Best Russian Imperial Stout.
Yes, we pitched the yeast at 78 degrees.
Yeast was Sarfale S-04.
OG was 1.070
FG is 1.030 using a hydrometer.

I would agree that a fast ferment test (this)

I am worried about bottle bombs. I really think you should sacrifice a bottle and do a fast ferment test to make sure it's done, taking into account priming sugar. If there is a significant drop in gravity and the yeast was only dormant and not dead you could have a dangerous problem.

seems to be reasonable advice.





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Re: FG questions
« Reply #13 on: December 04, 2017, 03:42:18 AM »
How do we do a fast fermentation test?
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Offline Stevie

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Re: FG questions
« Reply #14 on: December 04, 2017, 04:06:27 AM »