Stuck Fermentation - first GF millet malt beer

[Tinkerer]

Hi Gluten Free crew - first post but been watching for a bit.

My first shot at a gluten free beer: hazy IPA.
Problem: stuck fermentation! I'm about half way to my expected finish gravity.

Is the source my fermentation, or was it my mash?

2.5 gal target fermentation volume
Fermentables:
Pale Millet Malt (Grouse) 7.4 lbs
Pale Buckwheat Malt (Grouse) 0.7 lbs
Organic Flaked Oats 1.34 lbs

Milled to a coarse flour

Strike water at 160 deg F
Held mash at 158 deg F for 20 minutes
Raised to boiling (took almost 30 minutes) (boil at 204 deg F where I live in Colorado)
Transferred to my BIAB setup in a cooler, added cool water to drop the temp to 158 deg F
added 1/4 tsp of LD Carlson Amylase Enzyme
Held at 155 deg F for 40 minutes
Drained first runnings into kettle
Batch sparged with 168 deg F water, stand for about 5 minutes.
22.6 PPG for 3.2 gal and
preboil gravity = 1.067

60 minute boil with Mosaic Citra and Motueka added at flameout with a 45 minute hop stand.
post boil gravity = 1.090

one packet of Safale US05 yeast, rehydrated and pitched in the fermenter

Since I didn't want a 10% ABV, I added boiled & cooled water to bring the gravity to 1.064 around 2-3 hours after pitching yeast.

OG = 1.064
Ambient temp for fermentation:
Day 1: 68 deg F
Day 3: 65 deg F

Day 8 gravity = 1.034
Day 12 gravity = 1.032
At this point I was concerned about the stuck fermentation. I swirled my fermenter to rouse the yeast, and moved the fermenter to 70 deg F ambient.
Day 17 gravity = 1.032

So, what gives?
A yeast health problem? I've been an all-grain barley brewer for almost three years and used US05 yeast extensively. My prior beers usually finish around 1.009. That's with a single pack for 5gal batch. This was a 2.5 gal batch.
A mash problem?

If a mash problem ... I'll fix it next time
Any tips to resuscitate this beer? I'd like it to finish down at 15 points if possible. Pitch more yeast?

Thanks!

 

[Silly Yak]

According to How To Brew the top causes for stuck fermentation are #1 Too Cool and #2 Weak yeast/Underpitched. So if you moved the fermenter and are still seeing this issue I would say you need to add more yeast.

"The problem is most common with higher-gravity beers, those with OG's greater than 1.078."

 

[mredge73]

Several things may have contributed, hard to point at one thing in your process.
The initial 20 minute mash was high at 158F, if enzymes are available they will create long chain sugars that will not ferment out leaving you with a full bodied beer.
Amylase is most active around 148F so you are a bit high on this step.
I forget the science term for sugar poisoning, but one reason why you pitch so much yeast in a high gravity brew like this is because a large amount will die off quickly. Pitching more will insure that enough survive to kick off fermentation. So it would have been better if you diluted before you pitched your yeast.

As far as saving it, if it is a yeast issue rousing it and warming it is probably the best you can do.
If it is a mash issue you could add more amylase, it will dry it out some and eventually stop once it reaches its branch limit.
As a last resort, Beano pills contain a amylase-like enzyme that has a higher branch limit and can dry it out even further.
Good luck

 

[KeinGluten]

Did you taste it and did it taste sweet still? I'm wondering if it's possible that you had poor sugar conversion for some reason and the wort is not very fermentable.

 

[rjmaillie]

I had the same low attenuation issue in my first few all grain gluten free brews. Your problem (as was mine) may be lack of a beta amylase. The powdered LD Carlson stuff is alpha amylase only so you are ending up with the long chain sugars that Mr Edge was alluding to above. It won't help with this brew but for next time use something like Diatase Enzyme from EC Kraus. I ended up drinking those early beers ... they were unbalanced and sweet, but drinkable.