"It's not clear to me what problem you're trying to solve.

But an FG of 1.2 isn't a good assumption, even if you intended to write 1.020 ... that's way high for sugar. Using a value in the range [0.990 .. 1.000] would be reasonable."

I think you're getting wrapped around the axle a tiny bit.

All of my sugar washes have finished at 0.996 or lower. Keep in mind that it's all sucrose, so you don't end up with with a bunch of dextrins that the yeast are unable to metabolize like you do when you do one of your AG brews. S cerevisiae generates its own invertase so it has no problems breaking down the sucrose into glucose and fructose. Those dextrins will increase your gravity, but the yeast won't be able to convert them, so you'll end up with a higher FG.

Another thing to consider is that the yeast don't care about the FG. I've used plain old baker's yeast, wine yeasts, and ale yeast. The do care about the OG (osmotic shock) and the alcohol content (as alcohol is an inhibitor), but not the FG in and of itself.

I also don't get too concerned about the potential alcohol content (PA). I just worry about the OG (to avoid osmotic shock). I just like to keep the OG at (or below) 1.080, that's worked well for me ... the alcohol content is just a side effect. That said, I just use 46 ppg as an estimate for how much sugar to use. So in a six gallon wash at 1.080:

6 x 80 = 480 points
480/46 = 10.5 lbs of sugar

To keep things simple, I'll just use 10 lbs sugar topped off to 21 - 22 liters ... which will put my gravity right where I want it.

--JB

"If you start with a starch source you will most likely end up with with at least some dextrins ... if your FG is below 1.000 for an AG mash, I'd say you're doing pretty darn good. There's a bunch of things that enter into the equation, like the amylopectin content, the classes of enzymes in your mash, their concentration, time, temperature, pH, etc. etc. Then you need to get that cracked corn cooked-out so the enzymes can do their job. Regardless, glucoamylase can work on both the alpha- and beta-limit dextrins if you consider them a problem ... I believe the beer guys are still arguing over the whole ""mouth feel"" thing. :)

If you want to dig into the whole corn mashing thing, I'd recommend you take a look around modern distiller. There's a lot of corn experimentation going on there both with malt and without (using commercial enzymes). Take a look in the mashing topic ... and don't forget to look under the ""All grain"" sub-topic at the top (it's organized a bit weird). I think you'll find lots of good info that'll suit your interests.

Regards,
--JB"