Wow, homemade vinegar. Curl your toes!
OK, I finally figured out how to convert my almost 2 year old hard cider into vinegar -- I put it into a large plastic food tub (got it at a restaurant supply, wasn't cheap but I'll have it for years) so it had a lot of surface area, then inoculated with some organic raw vinegar from Whole Foods.
It took about 5 weeks. Formed a big solid, slimy, kind of rubbery mat of "mother" on top.
I strained, pasteurized, and bottled it almost 2 weeks ago now.
I used some yesterday on a marinated bean salad/salsa kind of thing.
I must say, this stuff is STRONG. I was worried that it might not come out strong enough to be safe should I want to try pickling with it. No worries there, it just about curled my toes.
I will do the right thing and actually test it properly before using it for pickling this summer, but in a side by side taste test with commercial cider and white vinegar, mine is definitely more acidic by a good deal.
I ended up with 7 1/2 gallons.
I also saved the mother -- I cut her up into pieces and popped them into the freezer. I don't know if this will work, but I suspect it will.