1968

If it goes under 64 or so, it can flocculate out, but that doesn't seem super likely. You can swirl if you it poops out early, but there's no reason for that to happen unless your ambient is lower than 65.

The fermometer reads the temperature on the back, not the ambient on the front.

It depends what he pitched it at. If his room is 66 ambient and the beer was 58 when he pitched, its not out of the realm of possibility it hasn't ever reached the current ambient temperature. A full carboy has a lot of thermal mass and the difference between 58 liquid and 66 ambient isn't enough to expect it to shift particularly quickly towards ambient.

 

What was your grain/extract bill, your mash temp (if all grain), and your mash length (if all grain)? Your attenuation might be finished. Published attenuation expectations (like 67-71% in this case) can sometimes be misleading.

 

Right, so what was the recipe?

 

Based on that grain bill, mash temp, mash length, and yeast strain, I would have expected (in my system) attenuation in the neighborhood of 74%. You may well have a bit further to go. Did you take gravity readings 2-3 days apart? That could help determine if fermentation is really stuck, or just slow. In either case though, a temperature bump couldn't hurt at this point.

Given all the information, I wonder if your yeast is tired. How much yeast did you pitch? And how did you oxygenate?

 

It sounds like you had plenty of yeast and O2.

 

That final gravity might be about right. Mashing above 150 with that yeast and a substantial amount of crystal malt, that yeast is going to struggle a bit to get through everything.

 

Sam, I took note of “Mashing above 150 …” So, you expect a more fermentable wort with a mash of 150 vs. 152? I specifically ask this since Greg Doss presented results at the 2012 NHC of attenuation vs. temperature and his experiment indicated that fermentability reaches a peak at 153°F:

• 150°F: Attenuation 83.02%
  
  
• 151°F: Attenuations of 83.02% & 83.96% (two test cases)
  
  
• 153°F: Attenuations of 84.91% & 84.91% (two test cases)
  

Greg also tested a large number of Wyeast yeast strains (51 strains in all) for the ability to attenuate the same wort and 1968 is pretty much at the mid-point with a value of 76%; the lowest value is around 74.5% and the upper value is around 79% (excluding 3711).

Cheers!

 

Pretty much any professional brewing text cites 145F (Well, 63C) as the optimal mash temperature for maximum fermentability. Raising temperature form there will lower fermentability. I'm not familiar with Greg Doss' experiment but it runs counter to established brewing science and I would be curious to see what his methods were.

 

If you're an AHA member, you can read his .pdf from the 2012 NHC on the website. Kai Troester did similar work, and found peak single infusion mash wort fermentability at 152F, just 1 degree off from Greg's results. I can't explain why they got different results than whoever first made the claims that ended up in the pro brewing texts.

I should add that Greg's trials only went down to 146F. Not sure how low Kai went, but it's all on his website.