Sorry,
I forgot to answer last night,
As a rule of thumb I use a water absorption of 0.1 gal per lb of grain
As far as doing the calc, An SG of 1.050 means 1 litre of that matrial weighs 1050 grams. and as 1L of water equals 1000 grams there are 50 grams of sugar.
Now comes the math, remember you will always have 50 grams of sugar or something which is changing the density. So if I reduce the water by 15 percent then I will have 50 grams of material per 850 ml of liquid which gives 50/850 =0.059 and then adding the thousand gives 1.059 as an SG. Or in your case going the other way 50/1150=0.043
or 1.043
Pretty sure I got that right, been a while, someone let me know if I missed
And no I wouldn't just add DME, I would evaporate the water until you got the right SG although in this case I would just ferment from 1.045 and live with it, remembering for next time.
Dogger
