Stout problem - Stuck Fermentation

[BottlesCansCraft]

Hi,

I recently brewed a BIAB batch of what I hoped would be an imperial stout with an initial OG of 1.084 and an expected FG of 1.017 on a 14 litre batch pitched with US-05.

After 4 days I checked the fermenation which gave a gravity reading of 1.040. I then checked a further 6 days later and the gravity is the same and seems to of stalled. Is there anything I can do to rescue this batch from its current stalled position?

I have had similar troubles before and double pitched US-05 but it didn't seem to help. Any help or ideas would be really appreciated

 

[foxy]

Hi,

I recently brewed a BIAB batch of what I hoped would be an imperial stout with an initial OG of 1.084 and an expected FG of 1.017 on a 14 litre batch pitched with US-05.

After 4 days I checked the fermenation which gave a gravity reading of 1.040. I then checked a further 6 days later and the gravity is the same and seems to of stalled. Is there anything I can do to rescue this batch from its current stalled position?

I have had similar troubles before and double pitched US-05 but it didn't seem to help. Any help or ideas would be really appreciated

Are you confident of the temperature of your mash?

 

[BottlesCansCraft]

Are you confident of the temperature of your mash?

66c/67c for 60 mins. How would mash temp influence a stalled fermentation?

 

[Rochefort]

Hi,

Mash temperature and pH could be the reason for the stalling, brew in a bag without recirculation will cause uneven mash temps and pH variations. It could also be underpitching, insufficient aeration or temperature swings during fermentation.

One thing you could do to rule out a bad mash would be to check the limit of attenuation with a fast ferment test on a small bit of the beer (Fast Ferment Test - German brewing and more).

 

[BottlesCansCraft]

Hi,

Mash temperature and pH could be the reason for the stalling, brew in a bag without recirculation will cause uneven mash temps and pH variations. It could also be underpitching, insufficient aeration or temperature swings during fermentation.

One thing you could do to rule out a bad mash would be to check the limit of attenuation with a fast ferment test on a small bit of the beer (Fast Ferment Test - German brewing and more).

Thanks. I dont have a pH reading from the brew, but I did check the temp throughout the mash to ensure it didn't fall to far from the target, and stirred for circulation periodically. US-05 states it 1 packet for 20-30litres so O thought underpitching wouldn't be an issue. I agitated the wort for quite a while once at the cooled temp of 20c for pitching to provide aeration. During fermentation, I don't have a specific temperature controlled chamber, but the wort is stored in an insulated cupboard that hardly ever strays from 20c.

 

[foxy]

Thanks. I dont have a pH reading from the brew, but I did check the temp throughout the mash to ensure it didn't fall to far from the target, and stirred for circulation periodically. US-05 states it 1 packet for 20-30litres so O thought underpitching wouldn't be an issue. I agitated the wort for quite a while once at the cooled temp of 20c for pitching to provide aeration. During fermentation, I don't have a specific temperature controlled chamber, but the wort is stored in an insulated cupboard that hardly ever strays from 20c.

There is no need to aerate your wort with US-05, I would be saying temperature is the most likely cause. Your pH did you add any salts? What I do with stouts and most beers add the none fermentables at mash out, that way you can easily adjust your pH as it is almost a constant on your pale malt bill. When I dough in I dough in at the lower end of the temperature, dough in at the high end can have an effect on how fermentable the wort is.

 

[Rochefort]

There was a definite need to aerate the wort in this case because the brew was underpitched!

US-05 has 6 to 10 billion cells per gram, for a strong beer you need 18 billion cells per litre (Pitch Rates | Wyeast Laboratories) so for 14 L that is 3 or 4 packs.

 

[foxy]

There was a definite need to aerate the wort in this case because the brew was underpitched!

US-05 has 6 to 10 billion cells per gram, for a strong beer you need 18 billion cells per litre (Pitch Rates | Wyeast Laboratories) so for 14 L that is 3 or 4 packs.

US-05 is a Fermentis dry yeast which they do not recommend aerating as there is no need, as with most dry yeasts of today.

 

[Rochefort]

US-05 is a Fermentis dry yeast which they do not recommend aerating as there is no need, as with most dry yeasts of today.

True enough for normal worts and pitching quantities, and I would agree with you if that was the case here.

The ergosterol levels get depleted at each replication and underpitching means more replications. The ergosterol levels that are 'built-in' to dry yeast are sufficient for a normal fermentation, which wasn't the case for this brew with the high gravity and low pitching rate. The levels of ergosterol can be sufficiently low that the yeast stop budding, and even if they keep replicating, the yeast struggle in the more hostile environment of high gravity beers. That is why the initial pitching rates are 2-3 times higher than for normal beers.

I'd only expect the finishing gravity to be 4-8 points higher if it was just pitching rate causing the problems, so there is another issue here. The mash might have been suboptimal or there is a temperature swing or spike during the fermentation. Stopping at halfway is usually a sign that the temperature has spiked during the consumption of glucose and maltose (this happens before halfway to terminal gravity/high krausen).

 

[foxy]

True enough for normal worts and pitching quantities, and I would agree with you if that was the case here.

The ergosterol levels get depleted at each replication and underpitching means more replications. The ergosterol levels that are 'built-in' to dry yeast are sufficient for a normal fermentation, which wasn't the case for this brew with the high gravity and low pitching rate. The levels of ergosterol can be sufficiently low that the yeast stop budding, and even if they keep replicating, the yeast struggle in the more hostile environment of high gravity beers. That is why the initial pitching rates are 2-3 times higher than for normal beers.

I'd only expect the finishing gravity to be 4-8 points higher if it was just pitching rate causing the problems, so there is another issue here. The mash might have been suboptimal or there is a temperature swing or spike during the fermentation. Stopping at halfway is usually a sign that the temperature has spiked during the consumption of glucose and maltose (this happens before halfway to terminal gravity/high krausen).

But we don't know the case here, it has stalled way to early. It is only 14 litres I would stake money on the mash temperature, with a side bet on underpitch but there should have been enough yeast cells to take care of 14 litres.