Lookin for a little help with a stuck fermentation

[Scott Wilson]

We recently did a wheat ale we split a 10 gallon batch 5 gallons got Conan yeast 5 gallons got American hefe. The starting gravity was 1053 it seems to be stalled out at 1.016, any thoughts? Scott

[BrianK]

I just typed up a reply to this, but for some reason it didn’t post. If I’m repeating myself here, please forgive me. As it sits now, your beer is about 4.8% which doesn’t seem too far off for either one of these styles. What final gravity are you shooting for? How does it taste? If it’s only slightly sweet, I think the carbonation might balance it out. If it’s cloying then it’s a whole different ball game. Some people say to pitch champagne yeast. I tried this ONCE but had zero success. Others say to pitch something clean and highly attenuative like us05 or nottingham. This worked for me once when I had used an English strain that crapped out before the work was done. Have you tried raising the temp? I know sometimes that helps lower it a few more points toward the end. Another theory is to pitch a saison strain. The idea is that most yeast driven flavors are produced early on in fermentation and if the saison yeast takes off, it will eat sugars but produce very little in the way of flavor. I have not tried this, but it doesn’t seem out of the range of possibility. Perhaps select a saison strain that produces less fruity/peppery flavors just to be safe (wyeast 3711 comes to mind). The thing that concerns me is this is a split batch and neither one seemed to hit the target. Is it maybe equipment failure? Thermometer not reading correctly resulting in a higher mash temp? Hydrometer not reading correctly etc.? I’ve had maybe 3 or 4 get stuck over my career. Some I have fixed/figured out the reason and others I haven’t. Good luck. Keep us posted, I’m interested to hear how it turns out.

[Mick S]

Resurrecting this thread after Steve’s posted about the issue on GroupMe. My thoughts…

– The reason champagne yeast doesn’t revive a stuck fermentation is that champagne yeast (at least most champagne strains) can’t eat maltotriose and is not very good at eating maltose. By the time a fermentation is “stuck,” the simpler sugars (glucose/fructose/sucrose) tend to be gone already, and champagne yeast can’t do much/anything with the more complex sugars remaining.

– Regarding most yeast driven flavors being produced early in the fermentation…I agree, sort of. For esters specifically, I prefer to say that the stage is set early in the fermentation, i.e. the initial conditions in the wort will determine much about how the esters will evolve later. I say this because yeast don’t actually make esters right away. They make fusel alcohols, which are later brought back into the cell and converted to esters. (This is why a fusel bomb can sometimes clean itself up given enough time with live yeast. Sometimes people talk about fusels “aging out,” but the bulk of what’s really happening is conversion to esters by yeast.)

– My recommendation for unsticking a fermentation would be to pitch a yeast that has attenuation characteristics as close as possible, given the grain bill and mash conditions, to the attenuation desired, as long as the current ABV of the beer isn’t close to bumping up against the new strain’s ABV tolerance. Pitching a saison strain could certainly work, but if you’re not trying to make a beer as dry as a saison, then you’re likely to end up with a beer that’s drier than desired.

---Mick S (aka VikeMan)

[Steve]

Very informative reply, Mick. I was never aware that the esters were first fusels. However it makes sense. What I’m particularly curious about is whether you can truly avoid saison like qualities if using the yeast for Something like restarting a fermentation. I have an interest in empirically testing that. Unless it’s already definitive. Then what’s the point.

[Mick S]

To test this, I think you’d need to brew a big beer, maybe something like a barleywine, with a yeast strain that should quit before attenuation is finished, due to its ABV tolerance. e.g., Wyeast 1968 has a tolerance of about 9%. I don’t know if there are any ale strains that have a lower tolerance. No yeast nutrient, no starter…stack the deck against the primary strain to keep it from over-achieving. Hopefully the yeast would quit with enough fermentable gravity left to really test the saison yeast’s impact on the flavor.

I suspect that whether or not the saison flavors show up will depend on how much carbohydrate the saison yeast has to work with. Let’s say that the saison yeast gets another 4% ABV out of the wort. My guess would be that the saison character might be noticeable…think about how much saison character you get in a little grisette. OTOH, that character would be diluted somewhat by the character of the stuck base beer.

If the saison yeast doesn’t have many carbs to work with, I suspect it wouldn’t impart very much character, because there couldn’t couldn’t be much additional cell growth.

Another thought, since the pathway leading to esters is a function of (among other things) cell growth… I have no idea if the saison strain cells would recognize the dormant/half-poisoned 1968 cells as part of their viable/vital population. If so, there might be little or no growth of the saison strain cells…so few additional esters downstream. OTOH, if the 1968 population is ignored, you’d expect some growth and some additional esters downstream.

Sounds like a fun experiment.

---Mick S (aka VikeMan)

[Steve]

That’s a really good idea for how to approach this. My first thought was to purposely stall the fermentation by crashing the temp. But once temps are brought back up, the primary strain would get back to work, thereby introducing a variable into the process. A barleywine is on my docket anyway, so I will use your method on this beer. Obviously, I will share the results with the club.

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