Im curious how much if any residual sugar is left in the wash and if it would be considered low-carb. Also curious what it tastes like, vodka and water just tastes like water but what does sugar wash taste like? I actually made one once and called it water wine because I was curious but that was 15 years ago and I cant actually remember if I ever even tasted it. Might still be in a bottle on the shelf, or thrown out when we moved 6 years ago.
It really depends on the type of yeast. Using WLP001, Nottingham, and EC1118 I get it down to 1.000 to .998, so very little, but those I only target 8-10% ABV. I just did a batch with turbo yeast, was targeting 16% and got closer to 20%, FG .995. The 8-12% had a bit of a chardonnay flavor to it, while the 20% has a very faint wine flavor with a touch of alcohol. I found at the 12%+ range it doesn't come through in the final product near as much.
I use those alcohol dilution calculators to figure out my volumes, so I'll say I want 5 gallons of a 6.5% punch using 20% base, then use what it says for alcohol and for the "water" I calculate how much cans of frozen juice concentrate (they typically make 48oz per can). One thing to note, you'll end up with a LOT of pulp/gunk in the bottom of your keg (think of how much you get if you mix up just a pitcher, then times 11 or so cans). I have my diptubes cut about an inch off the bottom, and even then the first few pours are pure sludge, along with the last couple pours. I've thought about trying to filter some of that out during mixing with a fine mesh bag but may add an extra can to make of for potentially losing flavor. I'm also thinking of trying a batch using Prairie Moon concentrates, not wholly natural but this is just for a party so I doubt anyone will care.
Funny enough just a few weeks ago the local liquor store had a sort of fake Fireball on sale, $4.99 for 750ml, no liquor taxes (I'm in WA). Reading the bottle it's because they it's using a "wine base" and not distilled alcohol so isn't subject to the same taxes, which is essentially what I'm doing. This one tastes pretty nasty since I'm sure they are pushing the absolute max ABV they can from the sugar wine.
Cheers!