Maybe this will help:
Made about 3 weeks ago, still in primary, will rack to secondary on Monday.
24ish pounds of apples (Goldens were the only apple available at market that week--no tartness, but seem to have worked)
1.5lbs fresh ginger root
10lbs plain ol white sugar
So, we pretty much just cored all the apples and ran them through a food processor, which didn't take too long with two people. We put all that mushy stuff into a fruit bag (white strain bag bought from LHBS). Meanwhile, made a simple syrup of the sugar and about 3 gallons of water. Used the food processor to grate the ginger and mixed that into the apples, poured the simple syrup over the mix, and hoped the apples would let off enough juice to bring us to about 5 gallons or so, which they did (using a plastic bucket).
I can't remember what yeast we used, but I have it written down at home and will post if you're interested. We campden tab'd it, let sit overnight to stabilize temp and let the sulfites evaporate, then pitched the yeast the next day. It took about 2 weeks to ferment down, but I've pulled a glass (or three!) out of the primary for, ya know, scientific tasting purposes, and it's delicious.
It's certainly missing some of the ginger ale qualities (I'm in Detroit, so Vernor's sets a high mark), but it is delicious--I really like it on its own. I'll be doing another batch this week with Northern Spy apples, and might add some other things to it. It's throwing off some big ginger aroma and flavor, which I like, so it seems about 1.5 lbs of ginger did the trick for 5 gallons.