High FG, what happened?

[prjectmayhem]

I was recently making an oatmeal stout, taking a bit from Yooper's stout recipe with the following grain bill:
67% 2 row
6.7% coffee malt
6.7% flaked oats
6.7% victory
3.4% flaked barley
3.4% crystal 80
3.4% pale chocolate
2.5% carafa III

yeast: Imperial A07 (Flagship) - 2.1L starter with stirplate (overbuilt according to beersmith to allow 0.8L for storing yeast for next batch)


OG was 1.059 but after 2 weeks the FG stopped around 1.026

Potential problem 1 : I wanted to mash at 156F as per the recipe, so I added strike water around 172F and the mash ended up around 159-158F for the first 5min. before resting at 157F. Little than lower OG but ended at 1.059 after boil. Did the initial strike temperature denature all of my proteins so that they couldn't produce fermentable sugars?

Potential problem 2: This is the 3rd generation of overbuilt starters. As described above, I use the overbuilt starter method to generate yeast for the next batch. I keep the slurry without cold crashing so I am thinking I am not selecting for overly flocculent cells, but maybe someone knows better?

Potential problem 3: Started fermentation a little cold, around 64F and then let it warm to around 70F over the first 36 hrs. Then the beer got cold, chilling back to around 62F during high krausen. Would this temperature change be enough to shock a fully active fermenation?

Potential problem 4 : All of the above, RDWDWHAB.

Thanks!

 

[brewbama]

I vote potential problem no1 combined with all the crystal malts.

 

[prjectmayhem]

I vote potential problem no1 combined with all the crystal malts.

I would think it was that much crystal too, but its the same percentage of Yooper's award winning stout. It was definitely supposed to finish high, but more around 1.016...

 

[Przemek]

I think it’s problem no3. I’ve had that once with my brown ale. Yeast went to sleep. Try to gently swing fermenter. If it doesn’t help, I would add new yeast.

 

[CascadesBrewer]

Do you use software to calculate estimated values? What did that say? Have you brewed this recipe before? 1.026 seems in the general ballpark for the recipe you describe and a 156/157 degree mash.

 

[kh54s10]

I would say one and three. Your mash was too hot leading to a lot of unfermentable sugars. Then your fermentation was on the cold side then on the hot side then cold again. That couldn't have been good.

 

[prjectmayhem]

Do you use software to calculate estimated values? What did that say? Have you brewed this recipe before? 1.026 seems in the general ballpark for the recipe you describe and a 156/157 degree mash.

I use beersmith2 - and for most other recipes I hit the numbers +- 0.002 pts. I think it must be the mash temperature, I haven't tried to go this high before. lessons learned!

 

[hilts]

Have you tasted the beer?

 

[CascadesBrewer]

I use beersmith2 - and for most other recipes I hit the numbers +- 0.002 pts. I think it must be the mash temperature, I haven't tried to go this high before. lessons learned!

Looking closer at your recipe and plugging some values into BeerSmith...yeah it says you should finish in the 1.017 range, even with a 157F mash. I have an Oatmeal Stout that finish in the 1.022-1.024 range, but it also starts in the 1.070 range and uses an English Ale yeast. I am curious to hear how the final beer turns out.