I was given a few bottles of 14 year old champagne. The first bottle was flat but doesn't smell off. Can I use it to make vinegar?
Yes, pretty much any old wine, if it hasn't already turned into vinegar, can be made into vinegar. The best is to start with clean wine, but if it already tastes kind of funky just push it towards the final goal of becoming vinegar. You can let this happen naturally, or you can buy vinegar "mother".