It's just a glass jar with a spigot, I'm guessing it's about 2 gallons and it's maybe 1/4 to 1/3 full. It's only over the level of the spigot by a little bit, so I haven't pulled any out yet. I've just smelled it when I add some leftover wine, which isn't all that often since most people who come to my house drink beer. At this point I haven't bothered to test the acidity and I'm not sure I ever will. The alcohol is getting turned into acetic acid, 1 for 1, CH3CH2OH becomes CH3COOH, right? Since all of the wine I'm adding is 11-13%+, I'm going to assume it balances out to about 12% or more acidity. So if I dilute it with 2 parts water to 1 part vinegar it will be in roughly the right range. I'll just taste it side by side with something of known acidity and see how my guess holds up. I probably have an acid test kit I could use though, and probably should test it at some point. I like the idea of not testing it though

I haven't really considered making balsamic. My understanding is that it is from white grapes cooked down, then aged solera style - starting in a large cask and moving to smaller and smaller casks as it ages and some evaporates. The authentic stuff is supposed to be amazing, but I've only ever had the cheaply made imitation stuff. It sounds like a cool project, I'm just not sure I'm up for it only to make vinegar