Crystal 120 and attenuation

UPDATE: I just racked this off the yeast today so that I could pitch an imperial stout on the cake. I decided to take a gravity reading and lo and behold, the SG is now 1.015 - right where it should be. It was at 1.020 for about 2 weeks. Good thing I didn't bottle it yet. I will let it sit for at least another week to make sure it is done. Just goes to show that you really are better off to be patient. Cheers!

I made an amber ale based on Ed's pale ale recipe as follows:

8 lbs 2-row
2 lbs vienna
1 lb crystal 120

60 min - .5 oz centennial
25 min - 1 oz cascade
5 min - .5 oz centennial
5 min - 1 oz cascade
0 min - 1 oz cascade

mashed at 152 for 90 min (in an effort to increase fermentability of wort)
batch sparge
60 min boil

OG - 1.057
Efficiency of 86%

Pitched 2L starter of US-05 - chilled and decanted first - (yeast washed from a previous beer). Visible fermentation started after 5 hours. Temp was 70 at pitch and never got higher during fermentation.

SG at one week was 1.020. Brought beer up from my basement to a room that is about 74 degrees and swirled it for several days. After another 2 weeks SG is still 1.020, which is 71% attenuation - just at the low end for US-05.

I don't care too much if this is the FG, as long as fermentation is done. Just curious as to why it is a little higher than expected. Is it just as simple as the pound of crystal 120? TIA


FYI - for what it is worth, the beer smells and tastes good. Going to bottle it sometime this week.

The C120L probably made the difference. You would have been better off lowering the mash temperature to improve fermentability.

Thanks. That's kind of what I thought, but wanted some of the collective wisdom from HBT.

So is there a way to help predict FG depending on the amount of crystal malts that are in the recipe?

One more bump.

That seems like a high FG to me even with a pound of crystal 120 in the mix. Have you calibrated your thermometer? 1-2 degrees can make a big difference. Did you aerate well before pitching?

Thermometer is fine - other beers finish at correct FG's. Aeration was good. I made Belgian pale ale the same day. Different yeast, but it finished at 1.011 from 1.051.

I recently made a partial mash Arrogant bastard clone which contained a pound and a half of crystal 120. Nottingham yeast took it from 1.070 to 1.013, so I would say the crystal alone is not to blame.

I'll add another anecdote:

I did an 1.070 IPA with a pound of C-120. Nottingham yeast took it down to 1.012.

There are a lot of variables, but I doubt the crystal malt was the culprit.

OOPS - forgot to add that I used a half pound of oatmeal also because I was thinking with the longer mash time and increased attenuation (which did not happen) that I might need it for the body.

Updated original post.