Is it really possible to restart a stuck fermentation?

[kombat]

I brewed an all-grain pale ale with an O.G. of 1.040 and a mash temperature of 148°F. After 2 weeks, the gravity was stalled at 1.025. So I added more yeast, gave it another week, and it fermented the rest of the way down to 1.008.

Said no one, ever.

We've all seen the threads where someone is seeking advice about a fermentation that stopped too high. It varies between "pitch more yeast," to "swirl the yeast up off the bottom," but does it ever really work? I mean, you might eke out a couple more gravity points, but has anyone ever heard of such remedies ever actually rousing the yeast into finishing a job they wouldn't otherwise have finished?

I'm not convinced there's actually such thing as a "stuck fermentation." Rather, I think what we're seeing is complete fermentation of a wort that is far less fermentable than the brewer intended, either due to an excess of unfermentable ingredients (too many crystal malts, or stale extract, boiled for the entire 60 minutes) or an unintentionally high/short mash. Or even just a way-high original gravity. Short of pitching an entirely different strain of yeast that will more readily consume those longer-chain sugars (and thus changing the character of the beer), has anyone ever actually heard of or experienced a case where a normal fermentation simply stopped, and was able to be successfully restarted by simply pitching more of the same yeast, or rousing the yeast that was already there? Or is this another persistent myth that has yet to fade away into obscurity?

 

[SmokeyMcBong]

Not with beer but I did 5 Gallons of wine from juice concentrate that went from 1.065 to 1.025 in a month. I racked it to a carboy, intentionally taking a fair amount of yeast (ec 1118) with it. In about a week, it was at 0.998. Was it stuck at 1.025, not sure as I only checked on it once and that was at the one month mark. I do know that it picked up a lot of steam after the racking.

That makes me think that re-suspending the yeast in some cases might work to if not restart a stuck fermentation then to at least re-energize lethargic yeast. Just my 2c

 

[fivepointslow]

I put my tank 7 clone that had a OG of 1.077 and stuck at 1.040 into my bucket for secondary to dry hop and it fired back up again is already at 1.030 2 days later. So it is possible to get it going again. 10 more days and this is going into the keg....

 

[kombat]

So what's the scientific explanation for what's happening? Why would yeast stop consuming fermentable sugars if there are still plenty remaining in solution?

 

[Braufessor]

I have only had a really significant stuck fermentation.....ie. still up in the 1.03+ range........ and, I could not get it to finish out, no matter what I tried - I got some more, but still ended up horridly sweet/unfinished.

However, I have had some beers just not finish out for me the way I planned. Basically, instances where it just (for whatever reason) pooped out at 1.018-1.022...... I never had any luck "resuspending the yeast" and kicking in again. However, one thing I have done that has worked consistently is this:

*decant a bit of a 1056 (type yeast) starter (that is already going for another beer). Add it to about 300ml wort in a 1000ml flask. Let it get rolling again for 12-24 hours.
*Transfer the "stuck/unfinished" beer to keg and add the small 1056 starter (that is very active)to the keg of beer.
*seal it up, and let it sit somewhere in the 70-72 range for about 10-14 days.

The 5-6 times I have done this, it has fermented out another 6-8 gravity points and also carbonated itself in the keg.

Not really the same thing that you seem to be talking about though.

**Instead of a starter, you could probably harvest some krausen from an actively fermenting beer at day 2-3..... that might even work better. I would be curious if that might even be a good strategy for a "truly" stuck beer??

 

[Brettomomyces]

I have only had a really significant stuck fermentation.....ie. still up in the 1.03+ range........ and, I could not get it to finish out, no matter what I tried - I got some more, but still ended up horridly sweet/unfinished.

However, I have had some beers just not finish out for me the way I planned. Basically, instances where it just (for whatever reason) pooped out at 1.018-1.022...... I never had any luck "resuspending the yeast" and kicking in again. However, one thing I have done that has worked consistently is this:

*decant a bit of a 1056 (type yeast) starter (that is already going for another beer). Add it to about 300ml wort in a 1000ml flask. Let it get rolling again for 12-24 hours.
*Transfer the "stuck/unfinished" beer to keg and add the small 1056 starter (that is very active)to the keg of beer.
*seal it up, and let it sit somewhere in the 70-72 range for about 10-14 days.

The 5-6 times I have done this, it has fermented out another 6-8 gravity points and also carbonated itself in the keg.

Not really the same thing that you seem to be talking about though.

**Instead of a starter, you could probably harvest some krausen from an actively fermenting beer at day 2-3..... that might even work better. I would be curious if that might even be a good strategy for a "truly" stuck beer??

I have a beer at 1.016 right now that I wish would come down to 1.012...I had been toying with some kind of plan to handle it but I really like your process for that. It had stuck at 1.020, I moved it to a warmer spot and then added a pint of s-05 slurry, brought it down to 1.016 over the course of a week but I wish it would go further (it's a bastardized SNPA clone).

Question, but how big a difference in gravity would you need to carbonate in the keg? Like, is a 4 point difference enough to fully carb?

 

[Braufessor]

According to this link:
https://www.homebrewersassociation.org/forum/index.php?topic=2177.0

Kaiser's post at the bottom = .5 volumes per gravity point.

So, as a "general" rule, 2 volumes for 4 points. That would be on the low end of carbed. But, it would be partially carbed if you got those points and you could put it on CO2 to get the rest.

 

[McGarnigle]

*decant a bit of a 1056 (type yeast) starter (that is already going for another beer). Add it to about 300ml wort in a 1000ml flask. Let it get rolling again for 12-24 hours.
*Transfer the "stuck/unfinished" beer to keg and add the small 1056 starter (that is very active)to the keg of beer.
*seal it up, and let it sit somewhere in the 70-72 range for about 10-14 days.

The 5-6 times I have done this, it has fermented out another 6-8 gravity points and also carbonated itself in the keg.

I did this once too, and it worked. Sort of a delayed starter. (ADD: except no keg for me. Just did it with a pail.)

I'm skeptical about reviving "stuck" fermentations as well, where the same yeast that crapped out is supposed to get a second wind.

 

[Braufessor]

I'm skeptical about reviving "stuck" fermentations as well, where the same yeast that crapped out is supposed to get a second wind.

Same here. Whenever I have done this with success in regard to kegging, I was adding 1056 yeast to a beer that had not been originally fermented with 1056 usually...... I figure 1056 is so neutral that it will not impart much by finishing out 6-10 pts. Also, it is a pretty hardy/vigorous/attenuative yeast. 007 might be another good yeast for the job.

 

[jmcquesten]

I just made a dipa with 007 and it stopped at 1.018. It was a mostly extract batch with a mini mash. I hoped for a lower finish, but it did match what brewsmith said I should get. It may have been due to the cool temperature even though I moved it to 68 around day 5 and put the bucket on a heating pad. That helped me get from 1.020 to 1.018, but it looks like that's where it's gonna stay. It's not terribly sweet, but I wish it would have went lower. Not sure why beersmith had it finishing so high, but I assume it's the extract (9.5 # light dme, 1 # crystal 20, 2 # 2 row, 1 # Munich, 1 # sugar). I guess it could be the crystal too, but even when I deleted it, it didn't really have it finishing much lower. I'm bottling it, so the keg trick isn't an option. I did make a 2 liter starter with the 007. I'll see what it looks like this weekend before dry hopping. Hope to bottle the following weekend.

 

[TheMilkMan]

Just last week I had a pale ale stuck at 1.020 for four days, from 1.065. I was fermenting Pacman at 60 degrees. I raised the temp to 67 and swirled the carboy and squeezed out another 3 points over the next 2-3 days before it stopped again. Kegged it last night, hope it turns out somewhat decent.

Same ingredients I have used for multiple other beers. Using DME, all comes from the same 50 pound bag. I think in this case it had to do with temperature. I've done this beer before, but this is the first time I fermented at the very low end of the yeast range.

 

[Brettomomyces]

According to this link:
https://www.homebrewersassociation.org/forum/index.php?topic=2177.0

Kaiser's post at the bottom = .5 volumes per gravity point.

So, as a "general" rule, 2 volumes for 4 points. That would be on the low end of carbed. But, it would be partially carbed if you got those points and you could put it on CO2 to get the rest.

Cool, thanks for getting that link for me. That's a pretty easy figure to remember as well.

 

[Talgrath]

Generally speaking, no a stuck fermentation is stuck. Maybe with some swirling and finangling you can get a few extra gravity points, but that could just be that you would get that anyway if you let it be as the yeast is/was slowly working. I've read of people trying everything from repitching to extra amylase to raising or lowering the heat and it never seems to work. The beer is stuck, accept it, drink it and try to figure out where you made the mistake. Of course, this does come from a brewer that doesn't believe in "fixing" bad beers, so take it with a grain of salt.

 

[jmcquesten]

What would happen if some brett were pitched?