I've tried twice before to make vinegar, but without success. But as Ben Franklin said, if at first you don't succeed, try, try again...
When I cleaned out the freezer, I found a quart bag of apple cores and peels that I'd missed when I made the last batch of apple jelly, plus a bag of plums. The plum scraps went into one quart jar, and the apple scraps into another quart jar.
I filled both jars with filtered water (I thought that my first failure might have been from using our tap water which is chlorinated and what-all) and about 1/8 cup of sugar, covered the jars with a cotton handkerchief and let them sit on the counter for about a week. I was supposed to shake them gently once a day but it didn't happen that often.
Update 11/26, Thanksgiving Day - I think I might be successful this time, at least with the apples: the jar smells like vinegar. The plum jar doesn't yet, it still smells like sweet plums. The two times that I've tried this unsuccessfully have been using plums, so maybe that's my problem. I transferred a couple of spoonfuls of liquid from the apple jar into the plum jar, stirred both jars and put them away again for a few more days.
Update 12/2 - Even the jar of plums smells like vinegar now. I strained the fruit out and put the liquid into clean jars, covered them again with cloth and left them to "work" for awhile longer. I can't help sniffing them daily.
Update 12/9 - The plum vinegar smelled pretty strong, so I bottled it today in recycled sauce bottles. (I save all of the uniquely-shaped bottles that we use when they're empty.) The apple vinegar isn't as strong-smelling as I think it should be, so I am waiting a bit longer to bottle it.
Update 12/11 - Now I'm really excited! The apple cider vinegar smelled very vinegary this morning so I bottled it. There isn't a great quantity of it, just one bottle not quite full, but it had "mother of vinegar" in it. Success! I poked it into the neck of the bottle and then realized that I should have put it in something with a wider neck so I could get it out again later. Using a piece of "mother" in a new vinegar-to-be liquid is the easiest and most sure way to get vinegar.
I don't know what the difference was this year, but after two years of failure, both of my experimental vinegars worked. I wonder if the apple vinegar is easier to make? Perhaps transferring a little of the apple vinegar into the jar of plum vinegar was the secret? That's when things really started "happening". Whatever the reason, I am excited to know that it can be done, and that I did it.