Stuck Pressure Fermentation

[Murphyslaw11]

Hi all. I am looking for some advice regarding a very high FG on a pressure-fermented Oktoberfest. I suspect it is just a stuck fermentation, but I am wondering if my process created too many unfermentable sugars. I tend to gravitate toward the maltier examples of Marzens, so I used a double decoction mash for this brew. I brew on a Robobrew 35L Gen 3 and use Brewfather.

Grain Bill:
6 lbs Weyermann Munich I
4 lbs Weyermann Pilsner
1 lb Weyermann Caramunich I
1 lb Weyermann Vienna

Water:
Mash 5.5 gallons distilled water - added 3g CaCl2, 1g epsom, 3g gypsom
Sparge 2 gallons distilled water - added 0.7g CaCl2, 0.23g epsom, 0.7g gypsum

Mash steps:
-Protein Rest: 131F for 15 min (immediately after mash-in, decocted 6 qt thick mash)
-Heated decoction to 152F for 10 min Sacch rest
(pH of main mash tested: 5.2 at 71F)
-Beta Rest: 146F for 45 min (used Robobrew to raise temp) (Boiled decoction for 30 min during this step)
-Alpha Rest: 158F for 30 min (added back decoction to raise temp from Beta rest. 8 degrees short. Used Robobrew to raise it) (immediately decoct 6 qt for second decoction)
-Boiled decoction for 15 minutes, then had to clear stuck mash in Robobrew. I drained the wort, stirred and added rice hulls to the mash, the added all back into the Robobrew.
-Mashout: 170 F for 10 minutes. (Added decoction back to main mash to reach 170F but due to stuck mash, wort and grains cooled. Mash temp was at 155 after adding the decoction. Used Robobrew to raise to mashout temp).

Pre-sparge: 4 gallons at 1.062

Sparge:
-Initial runoff was extremely slow due to the mash becoming stuck again
-Raised sparge water to 178F.
-Added 1 lb rice hulls as soon as runoff was completed. No sparge issues.

Pre-boil: 6 gallons at 1.053
90 minute boil
0.7 oz Tettnang & 0.53 oz Perle @ 60 min
7.5 tsp yeast nutrient & whirlflock @ 10 min

OG 1.063 (right on target)

Chilled to 52F
Transferred to corny keg (w/floating dip tube) via splashing. Shook keg to further dissolve oxygen.
Pitched 2L starter of Wyeast 2633 Oktoberfest Blend.
Added spunding valve set to 12 psi
Fermented at room temperature (69F)

The spunding valve was steadily hissing on day 1, went crazy on days 2 and 3, and slowed to a quiet hiss on day 4. It hasn't hissed at all since. I sprayed some star san to see if it would bubble and it didn't, so I thought fermentation completed.
I tested the gravity and it read 1.024, which seemed very high (expected 1.010 - 1.014). It also tasted sugary sweet, not just malty like I intended. It did not have any fruity off flavors, however.

Again, I am hoping it is just a stuck fermentation, in which case I will shake the keg to agitate the yeast back into suspension. I have also contemplated adding table sugar.
If anyone can help me identify if I made mistakes in my process though, I'd appreciate any help coming up with a plan. Thanks in advance.

 

[JohnSand]

I don't pressure ferment, so maybe I'm missing something relevant. 1.024 does seem high, and like you, I suspect the yeast first. Shaking won't hurt it, warming might help. I wouldn't make any other changes for a few days.
Good luck, keep us posted.

 

[HM-2]

Hitting ~60% attenuation in a couple of days then slowly crawling down to FG over 2-3 weeks is fairly typical of many German lager yeasts IME.

Stick it in a corner and forget about it for a few.

How much pressure are you fermenting under?

 

[dtashmore547]

never done a decoction mash but I only ever pressure ferment at around 16psi, I recently had a stuck ferment when the temperature dropped to 6 degrees C, the yeast is under stress and needs higher temperature. my only solution was to put more yeast in plus additional nutrient and pushed up the heat to 25 degrees C, off it went again, I only produce English ales so you will need to adapt but pressure fermentation allows for higher temperatures on lagers. also check the current PH.

 

[HM-2]

16psi is substantially more than you need for effective pressure fermentation. 8-10 is plenty to gain all the benefits and less likely to stress or kill the yeast.

 

[Murphyslaw11]

Thanks everyone for the advice.

I don't pressure ferment, so maybe I'm missing something relevant. 1.024 does seem high, and like you, I suspect the yeast first. Shaking won't hurt it, warming might help. I wouldn't make any other changes for a few days.
Good luck, keep us posted.

I appreciate all of this. I cross posted in the all grain brewing category and got tons of input too. I shook the keg as per your recommendation but it didn’t seem to help. Others figured I created too many unfermentable sugars during the decoction. I bought more of the same yeast, made another starter, decanted and pitched but the FG only dropped to 1.021. A few people suggested amylase enzyme. I added 1.25 tsp (0.25 tsp / gal) per package recommendation, swirled the keg, and added heat wrap set to 77F at 10 psi spunding. I haven’t heard any spunding activity yet, but I also haven’t tested the FG since adding it 3 days ago.

 

[Murphyslaw11]

Good luck, keep us posted.

I am happy to report that the FG dropped to 1.011 after adding the amylase enzyme and placing it at 77F under 12 psi. Thanks to everyone in this thread for all of the help.

 

[Bassman2003]

I can only guess that your initial yeast pitch was not as healthy or as large as you expected. Pressure fermentation requires a lot of cells. But, you were at room temp which is a lot easier than lager temps.

Can you tell more about the yeast and starter prep? How old was the yeast and how long did the starter run for? 12 psi is not too hard on yeast so your situation is kind of a mystery since activity took off quite quickly.

 

[Murphyslaw11]

I can only guess that your initial yeast pitch was not as healthy or as large as you expected. Pressure fermentation requires a lot of cells. But, you were at room temp which is a lot easier than lager temps.

Can you tell more about the yeast and starter prep? How old was the yeast and how long did the starter run for? 12 psi is not too hard on yeast so your situation is kind of a mystery since activity took off quite quickly.

I did not note the date of the yeast packaging but my local homebrewer shop regularly restocks fresh yeast.

I activated the snack pack 48 hours before brew day and let it sit on my kitchen counter at 71F to swell. It was fully swollen in 4 hours so I pitched it to a 2L Erlenmeyer flask with 1/2 can (8oz) of propper starter and 8 oz distilled water. I let it spin on a stir plate for 24 hours. There was plenty of activity (not a huge Krausen but opaque and milky, smelled like fermentation). I measured the temperature frequently and it stayed between 69–71F.

After 24 hours, I stepped it up with a full can of propper starter and 16 oz distilled water. Again, there was plenty of activity except a large krausen and it stayed between 69-71F.

I pitched the whole starter to my brew at 52F.

Some potential mistakes that I made could be: not decanting. I fermented this in a corny keg. Since I did not decant the starter, there was almost no head space in the keg at the start of fermentation. I also did not let the pressure rise to 12 psi, I injected 12 psi CO2 (I did not think it would make a big difference since I didn't then purge the keg and there was no head space for CO2 anyway) and added spunding valve.

After the FG tested at 1.024 multiple times, I followed the same process with a new pack of 2633. It only dropped to 1.021.

I then used a tip from another thread I posted in the "All Grain & Partial Mash Brewing," which was the amylase enzyme process I noted above.

I cold crashed the beer and transferred it off of the yeast in the ferm keg to a serving keg. I pulled a sample and it tasted very young with a grassy and "homebrewy" flavor. I added 1/2 tsp gelatin finings per package recommendation. It is currently lagering around 38F. I plan to leave it there for several weeks.

 

[Bassman2003]

Thanks for sharing. Something seems strange. You have plenty of yeast to get past 1.024. Especially at the high temps (69F). Then more yeast only gets .003 gravity point more? Either measurement is off somewhere or the mash program did not execute the way it was thought.

One question, If you chilled to 52F, why not ferment at 52F @ 12 psi?

 

[Murphyslaw11]

Thanks for sharing. Something seems strange. You have plenty of yeast to get past 1.024. Especially at the high temps (69F). Then more yeast only gets .003 gravity point more? Either measurement is off somewhere or the mash program did not execute the way it was thought.

One question, If you chilled to 52F, why not ferment at 52F @ 12 psi?

I measured temps and gravities multiple times because I also questioned their validity, but they were consistent. Due to the answers on my other post, which I’ll try to link, I now believe the issues were due to my mash program as you pointed out. I am not exactly sure which part, but some speculation based on others’ tips: I double decocted highly modified malts including a large amount of caramunich, I should’ve let the first decoction rest longer; and/or my temperatures dropped too much when I had to clear a stuck mash by draining.

I chilled to 52F to ensure a healthy pitch per package instructions, but I didn’t ferment there because I didn’t have the space in a Ferm chamber. I had an Irish stout fermenting in there at a different temperature. To further detail my fermentation steps, I pitched at 52, added spunding valve at 12 psi, and let the temperature free rise. I had the Inkbird hooked up just so I could see the temperature with the probe, but did not attach heating/cooling elements. It got up to 69F, which is the ambient room temperature of my living room.

Also in retrospect, I believe another mistake was to inject 12psi instead of letting the pressure rise to 12 psi from fermentation. I probably caused a lot of yeast stress

 

[Murphyslaw11]

Due to the answers on my other post, which I’ll try to link

https://www.homebrewtalk.com/thread...is-10-points-high.733883/page-2#post-10409953

 

[Bassman2003]

I measured temps and gravities multiple times because I also questioned their validity, but they were consistent. Due to the answers on my other post, which I’ll try to link, I now believe the issues were due to my mash program as you pointed out. I am not exactly sure which part, but some speculation based on others’ tips: I double decocted highly modified malts including a large amount of caramunich, I should’ve let the first decoction rest longer; and/or my temperatures dropped too much when I had to clear a stuck mash by draining.

I chilled to 52F to ensure a healthy pitch per package instructions, but I didn’t ferment there because I didn’t have the space in a Ferm chamber. I had an Irish stout fermenting in there at a different temperature. To further detail my fermentation steps, I pitched at 52, added spunding valve at 12 psi, and let the temperature free rise. I had the Inkbird hooked up just so I could see the temperature with the probe, but did not attach heating/cooling elements. It got up to 69F, which is the ambient room temperature of my living room.

Also in retrospect, I believe another mistake was to inject 12psi instead of letting the pressure rise to 12 psi from fermentation. I probably caused a lot of yeast stress

Thanks. A natural build compared to a starting pressure is a choice. The higher the start and pressure ends up showing more characteristics of pressure fermentation. I run my IPAs at 30 psi from the start. Yes, it requires more yeast but the outcome is more like a larger conical/pro brewery. I do not think 12 psi is too detrimental to the yeast as 15 psi is supposed to be where CO2 starts to become toxic to them.

 

[VTMongoose]

https://pubmed.ncbi.nlm.nih.gov/16082465

"Below 50 MPa (500 atm) yeast cell morphology is unaffected whereas above 220 MPa wild-type cells are killed."

500 atmospheres is 7,000+ psi.

I've pressure fermented as high as close to 50 psi (accidentally) before. Yeast can handle tons of pressure. How else do you think Belgian yeasts are easily able to carbonate to 4+ volumes of CO2? Those corked and caged bottles you see on the shelf can easily have 70 psi in the headspace at room temperature.

I think the original problem happened in the mash. The fact that the yeast are responding to the addition of a mash enzyme and not anything else is a strong indicator that unfermentable short-chains are being converted into sugars allowing fermentation to continue. It's possible the mash wasn't stirred enough or somehow the temperature wasn't measured correctly.

My guess: when OP set the robobrew to 145, most of the mash never got close, maybe it got up to 135-137 (was it checked with a long thermometer, in multiple places? Was it stirred?). Beta-amylase isn't doing anything. OP adds the decoction back. He starts at 150, low, because the mash was already low, now he's actually saccharifying, but he immediately ramps to 158 and it ends up heavily favoring alpha activity and producing a very unfermentable mash.