I am in the middle of trying to brew 6 gallons of high ABV cider. I had read that it is often better to add sugars to the brew in increments during fermentation, rather than all at once. I believe the reasoning had to do with the yeasts ability to kick off fermentation being reduced if the OG was too high.
So...I started with an OG of 1.087 with the sugars being either from the juice I used, or from the dark and light sugar I added. Six days of vigorous fermentation later, bubbling stops and I am at a specific gravity of 1.000, which would indicate an ABV of about 11-12%, depending on what equation you use. I am using a Red Star Premier Cuvee' yeast, which supposedly can go to 18-22% ABV. I taste the sample that I floated my hydrometer in and it wasn't bad. I bit dry, but a little bit of apple flavor left. I wanted this stuff to ferment a bit more to get the ABV into the 12-13% range, so I racked it to a secondary and tossed in another pound of sugar (dextrose) and a bit of yeast nutrient dissolved in a small amount of water. Fermentation kicks back off.
My question is: Is it correct for purposes of ABV calculation to use an OG reading based on what the OG would have been had that extra pound of sugar been in the brew from the beginning? In other words, since dextrose raises the specific gravity by .046/gallon, should I just add on one sixth of that, say .0075, to my original OG for a new and improved OG of 1.0945? For purposes of this calculation let's assume the amount of additional water added was not enough to matter.
My eventual plan is to break this batch up into 5-7 smaller containers, pasteurize some of them to keep it at that 12-13% ABV then backsweeten them with various herbs, berries and honey. I will probably keep feeding the yeasts on several batches just to see how close to 20-22% ABV I can get.
Thanks in advance for any feedback you can give me.