Terminal gravity calculation a bit high?

[Steve973]

I was trying to come up with a duvel clone, and I tried two ways of going about it. First, I tried 28 lbs of pils malt for a 10 gallon batch... 12 gallons before the 90 minute boil. BTP was claiming an OG of 1.073 and a FG of 1.018. That seems a little bit high for pils malt and Wyeast 1388 (belgian strong ale). I figured that I could decrease the FG by making light candi sugar total about twenty percent of my fermentables (17.9% to be exact). This yielded an OG of 1.082, which is nice, but the FG shot up to 1.020.

This seems to be a bit strange... I would expect this brew to attenuate down to 1.015 or somewhere around there. Wouldn't the candi sugar ferment completely?

[jeff]

I was trying to come up with a duvel clone, and I tried two ways of going about it. First, I tried 28 lbs of pils malt for a 10 gallon batch... 12 gallons before the 90 minute boil. BTP was claiming an OG of 1.073 and a FG of 1.018. That seems a little bit high for pils malt and Wyeast 1388 (belgian strong ale). I figured that I could decrease the FG by making light candi sugar total about twenty percent of my fermentables (17.9% to be exact). This yielded an OG of 1.082, which is nice, but the FG shot up to 1.020.

This seems to be a bit strange... I would expect this brew to attenuate down to 1.015 or somewhere around there. Wouldn't the candi sugar ferment completely?

If you think the terminal gravity is high then increase the apparent attenuation. Belgian ales often have high apparent attenuations because of the candi sugar.