Happened to start reading about the millions of uses for distilled vinegar. I gotta say, for simple stuff its pretty amazing and quite handy. Its really just alcohol thats gone beyond the drinking stage and left to turn into acetic acid right? So my question is this. If you left out a covered jar of fruit juice at room temp. for a few months, would it eventually ferment and turn into vinegar? Or do you need to add something. And from that, how do you make distilled vinegar?

There are a lot of sources on the internet to instruct you, but the one thing you add is "mother of vinegar."

Mother of vinegar is a substance composed of a form of cellulose and acetic acid bacteria that develops on fermenting alcoholic liquids, which turns alcohol into acetic acid with the help of oxygen from the air. It is added to wine, cider, or other alcoholic liquids to produce vinegar.

Mother of vinegar can also form in store-bought vinegar if there is some non-fermented sugar and/or alcohol contained in the vinegar. While not appetizing in appearance, mother of vinegar is completely harmless and vinegar does not have to be discarded because of it. It can be filtered out using a coffee filter, or simply left in and ignored.

If you want to make distilled vinegar, then you would need to distill it.

Thanks for the info. Been reading quite a bit but can't find difinitive answers on a couple things. The only store bought vinegar that contains "mother" is unfiltered and unpasturized, like some brands of apple cider vinegar, correct? And, is it safe to say, aside from a possible loss taste, all vinegar has an indefinite shelf life?

Not sure about indefinite shelf life. I've seen vinegars that had some growths floating around in them, and I was not too enthusiastic about trying them. They could have been fine to ingest and also had other uses even if they were not fine to ingest.