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Old 08-17-2012, 01:22 AM   #1
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Default Another stuck lager ferment

Brewed my first lager, an Oktoberfest. Ten gallon batch, 1.056 OG from BCS

Pitched a 4.5 L starter (starter fermented at 55 deg F for 5 days, then was crash cooled), when the wort was at 48 deg F.

Kept at 50 deg F for 4 weeks. SG was 1.032
Raised to 65 deg F for a diacetyl rest and to get the yeast kicking for 7 days. Swirled carboys to rouse yeast.
SG is now at 1.026 at almost 6 weeks.

What now? Pitch a new starter to reach FG? Rack and lager? Throw onto a pac-man yeast cake that is currently fermenting when it's done?

Any thoughts/suggestions would be appreciated.

KJ

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Old 08-17-2012, 01:26 AM   #2
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Originally Posted by kj23 View Post
Brewed my first lager, an Oktoberfest. Ten gallon batch, 1.056 OG from BCS

Pitched a 4.5 L starter (starter fermented at 55 deg F for 5 days, then was crash cooled), when the wort was at 48 deg F.

Kept at 50 deg F for 4 weeks. SG was 1.032
Raised to 65 deg F for a diacetyl rest and to get the yeast kicking for 7 days. Swirled carboys to rouse yeast.
SG is now at 1.026 at almost 6 weeks.

What now? Pitch a new starter to reach FG? Rack and lager? Throw onto a pac-man yeast cake that is currently fermenting when it's done?

Any thoughts/suggestions would be appreciated.

KJ
Boy, that's a tough one. Which yeast strain are you using?
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Old 08-17-2012, 01:30 AM   #3
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Wyeast 2487 - Hella Bock

Add a different yeast (after making a starter)?

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Old 08-17-2012, 02:36 AM   #4
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Leave it. 1.026 is not that bad. It's supposed to be malty anyway. Whatever marginal improvement in attenuation you get at this point is not likely to be worth it. Enjoy your O-fest and work hard next time to get better attenuation.

As an aside I made a phenomenal doppelbock last year that finished at 1.026. Yeah, the OG was higher but...it didn't concern me that it finished well over 1.020.

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Old 08-17-2012, 12:00 PM   #5
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Quote:
Originally Posted by kj23 View Post
Brewed my first lager, an Oktoberfest. Ten gallon batch, 1.056 OG from BCS

Pitched a 4.5 L starter (starter fermented at 55 deg F for 5 days, then was crash cooled), when the wort was at 48 deg F.
I think you're SOL this time. But the lesson here is that this was a significant under-pitch by more than 40%.

For a 10 gallon batch, you needed close to 800B cells, and assuming 100% viability and a sitr plate, you only got about 450B cells. This is why you got a stuck ferment.

Also, what might help in the future is to gradually nudge the temp up after you have hit 75% attenuation, up to the mid-50's, and then up in the diacetyl rest range of 60F+. It is most likely too late at 4 weeks to then decide to raise the temp.
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Old 08-17-2012, 12:15 PM   #6
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Underpitching by 40% doesn't explain the stuck ferment. Heck I've used literally one-fifth your amount over a dozen times and never had a stuck ferment (500 ml starters were the norm in the 90s). So there's probably something else going on. Lack of aeration, temp swings, who knows.

Considering your current attenuation, I personally wouldn't bottle this yet.

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Old 08-17-2012, 05:03 PM   #7
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Underpitching by 40% doesn't explain the stuck ferment. Heck I've used literally one-fifth your amount over a dozen times and never had a stuck ferment (500 ml starters were the norm in the 90s). So there's probably something else going on. Lack of aeration, temp swings, who knows.

Considering your current attenuation, I personally wouldn't bottle this yet.
Don't think it is related to temperature swings, the OP said he kept it at 50F for 4 weeks. Insufficient aeration or perhaps a very high mash temp are possibilities, but given the information provided the mostly likely cause is insufficient yeast.

Either way, this is a clear case of under-pitching. Several technical brewing textbooks cover this situation (under-pitching and related problems) in great detail.
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Old 08-17-2012, 05:35 PM   #8
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Underpitching makes sense. Thanks for all the replies. I need a bigger flask!

But what to do with it now? Rack it? Re-pitch? Other ideas?

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Old 08-17-2012, 05:45 PM   #9
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You don't need a bigger flask, but you could learn about doing step-up starters. Consult yeastcalc.com for help with step sizes, etc.

For now...rack it and lager it.

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Old 08-18-2012, 05:46 AM   #10
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I would also think about Oxygen if you are going to do large batches of lager...it has a significant impact on early yeast health and also helps control ester formation. Yeast only divide 2 or 3 times during fermentation so a low population with low initial oxygen just won't attenuate well especially when gravity is over 1.050. Fermentation time takes twice as long for a 1.050 wort when compared to a 1.033 wort.

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