Stuck Fermentation or Hot Side Problems...

[Brian Parfitt]

Greetings all.

I've been a hobbyist brewer for a couple of years, starting with extract, but graduating a few years ago to all grain.

I have an oatmeal stout currently fermenting that appears to have stalled in fermentation. OG of the beer was 1.060 and estimated FG was supposed to be 1.016. After two weeks in primary, the gravity measured 1.030. I suspected my fermentation stalled due to cooler then expected temperatures (~60-62F) in the fermenter. I moved the fermenter to a warmer location and observed a little airlock activity, but it again slowed after a day or two.

Last week after 4 weeks in the fermenter, I again measured the gravity to be 1.028-1.030. I decided to add a second yeast packet and mixed up a starter. Again, I had a little airlock activity, bit it settled down after a day.

My question is this, if the gravity ultimately settles to that 1.030 value, what will I be left with? I understand that one of the causes for the high gravity could have been a mash temperature that was too high. I recall that the mash thermometer was a touch high ~158 for some of the mash. So basically, non fermentables in the wort contributing to a higher then expected gravity. Is the batch ruined/lost?

Thanks in advance for the help/suggestions.
Brian

 

[jrgtr42]

More details on what exactly your recipe, process and so forth is will help us diagnose what's going on.
High mash temp can easily result in higher than expected FG - depending on how long and when it was that high.
I don't think the fermentation temps are as big a deal - depending on your yeast. I usually keep mine at 60 - 62 ambient - because I don't have a way to control temps, and I've found my beer ends up better that way, at least to my taste. I do see fermentations taking longer than at mid or high 60s, though. (amazing what a difference a couple degrees higher or lower can make.)

 

[Brian Parfitt]

More details on what exactly your recipe, process and so forth is will help us diagnose what's going on.
High mash temp can easily result in higher than expected FG - depending on how long and when it was that high.
I don't think the fermentation temps are as big a deal - depending on your yeast. I usually keep mine at 60 - 62 ambient - because I don't have a way to control temps, and I've found my beer ends up better that way, at least to my taste. I do see fermentations taking longer than at mid or high 60s, though. (amazing what a difference a couple degrees higher or lower can make.)

Thanks for the reply. Some more details below.

Grain Bill was:
8lb 10 oz Maris Otter Pale Malt
1 lb flaked oats
12 oz Victory Malt
8 oz Black Patent Malt
8 oz Crystal 80L
6 oz Pale Chocolate
6 oz Chococlate
4 oz East Kent Goldings (60 min boil)

Wyeast English Ale Yeast

Mash 60 mins at 154

mash temp was observed at 158 for at least 30 mins during Mash. The thermometer I used appears to have a slow response time and swung up past my target of 152-154.

Batch sparge with 168F - Measured with separate thermometer (I use a Mash and Boil to heat sparge water and take readings right off the display)

Mash was done using my 10 gal picnic cooler with screened bottom. This has given me good reliable 75% + efficiency for years. (I struggle to hit 65% with the Mash and Boil even when recirculating which is why it has been relegated to a water heater.

Chilled with immersion coil chiller.
Yeast pitched at 68F
Primary two weeks before first gravity reading taken.

 

[brownni5]

Lots of unfermentable grains there, coupled with a relatively high mash temp and a (presumably) low attenuating yeast could lead to a higher than expected final gravity, but that still seems high...

 

[Brian Parfitt]

I checked the gravity yesterday.. It may have dropped a little bit 1.026 down from 1.030, but not much of a change. I'll let it ago another week and check again, but it seems like that is where it is going to settle. The recipe predicted an FG of 1.016 and OG of 1.062 with an expected ABV of around 6%.

Looks like I'll wind up with 4.7% if I'm lucky. Bummer.

 

[Yooper]

I checked the gravity yesterday.. It may have dropped a little bit 1.026 down from 1.030, but not much of a change. I'll let it ago another week and check again, but it seems like that is where it is going to settle. The recipe predicted an FG of 1.016 and OG of 1.062 with an expected ABV of around 6%.

Looks like I'll wind up with 4.7% if I'm lucky. Bummer.

Make sure your hydrometer reads 1.000 in plain water to ensure your hydrometer isn't off, but I suspect with that high mash temp it could very well be done.

 

[couchsending]

No way that yeast could ever achieve 1.016 with that grain bill and that mash temp.

1968 is the yeast right?

It should have maybe got to 1.020 but that’s it. You need to mash that yeast pretty low in order to get decent attenuation. It’s the yeast I use when I want a higher FG which is generally dark beers. Often times I’m looking for anything north of 6.5% to stop around 1.030. 1968 works every time with a high mash temp and a bunch of dark crystal.

That yeast does fine at lower temps so it wasn’t the temp that stalled it although that didn’t help.

If you want a lower FG you can pitch a bit of US05 and warm it to 70. Should get closer to your FG.

 

[Tobor_8thMan]

I think your mash got stuck due to the gumminess of the oats. Next time using oats, throw in some rice hulls in the MLT.

 

[Brian Parfitt]

No way that yeast could ever achieve 1.016 with that grain bill and that mash temp.

1968 is the yeast right?

It should have maybe got to 1.020 but that’s it. You need to mash that yeast pretty low in order to get decent attenuation. It’s the yeast I use when I want a higher FG which is generally dark beers. Often times I’m looking for anything north of 6.5% to stop around 1.030. 1968 works every time with a high mash temp and a bunch of dark crystal.

That yeast does fine at lower temps so it wasn’t the temp that stalled it although that didn’t help.

If you want a lower FG you can pitch a bit of US05 and warm it to 70. Should get closer to your FG.

Sorry.. Correction here.. I used Wyeast 1084 (Irish Ale Yeast) per what was available at my LHS during the first part of the lockdown.

Not sure if that changes the analysis or not.

Either way, very much appreciate the feedback.

 

[Tobor_8thMan]

Sorry.. Correction here.. I used Wyeast 1084 (Irish Ale Yeast) per what was available at my LHS during the first part of the lockdown.

Not sure if that changes the analysis or not.

Either way, very much appreciate the feedback.

1084 and 1968 are not similar, as you note. From experience I do know 1968 drops clear, 1084 needs help.

Also, 1084, as per Wyeast, ferments at at 62 o 74F, but this doesn't take into consideration the increase in temp due to fermentation.

1.030 is way too high for bottling. Maybe kegging, but the brew isn't done.

 

[Brian Parfitt]

It's going into a keg. I'll watch it a bit longer before transferring.

Also - good suggestion on testing hydrometer. Will give that a look tomorrow morning.

 

[Brian Parfitt]

No way that yeast could ever achieve 1.016 with that grain bill and that mash temp.

1968 is the yeast right?

It should have maybe got to 1.020 but that’s it. You need to mash that yeast pretty low in order to get decent attenuation. It’s the yeast I use when I want a higher FG which is generally dark beers. Often times I’m looking for anything north of 6.5% to stop around 1.030. 1968 works every time with a high mash temp and a bunch of dark crystal.

That yeast does fine at lower temps so it wasn’t the temp that stalled it although that didn’t help.

If you want a lower FG you can pitch a bit of US05 and warm it to 70. Should get closer to your FG.

Would love to try working that FG down... Warm to 70 and Direct pitch single packet of US05? Any suggestions on rehydrating vs. direct?

 

[couchsending]

Would love to try working that FG down... Warm to 70 and Direct pitch single packet of US05? Any suggestions on rehydrating vs. direct?

You definitely don’t need a whole packet. You only need to drop it a few points right? I’d add maybe 2g of US05 to some wort (depending on how much room you have in your fermenter) and let it start to ferment then pour that into the stuck fermentation. That should be more than enough yeast to drop the gravity to something a little closer to what you were looking for.

 

[doug293cz]

If you want to get the FG lower, you could try adding some alpha amylase enzyme (not glucoamylase/amyloglucosidase) to the fermenter. This will take several days to work since the temps are much lower than mash temps. If your issue is dextrins that are bigger (longer chains, higher molecular weight) than limit dextrins, the amylase can break the some of the dextrin down into fermentable sugars.

And just to double check - you are using a hydrometer (and not a refractometer) to measure SG, correct?

Brew on