Fruit Scrap Vinegar
The peelings of a pineapple makes one of the more delicious vinegars; it's called for in many Mexican recipes. Any fruit scraps will work well though: apple peels and cores, bruised fruit, overripe bananas, overripe berries, grapes or cherries...
Put any of the above fruit in a clean, food-safe container and cover with sugar water--1/4 cup sugar to one quart of water. Honey can be substituted for the sugar, but it will take a bit longer. You only need enough sugar water to cover the fruit. Put cheesecloth on top to keep insects out. The wider the top, with greater surface area exposed, the less time fermenting will take.
After about a week, when you notice the liquid darkening, strain out the fruit and let the liquid sit another couple of weeks. Stir it occasionally. It's ready! Don't worry about leaving it too long, as it's a staple product and won't turn into anything else.
You may notice a film collecting on the surface. It's edible and nutritious, nothing wrong. This is the "mother" of you vinegar and can be used to start a new batch (instead of fruit). If your "mother" has sunken below the surface with solid blobs, it is inactive. You can strain it out or use it as vinegar (or toss it).
If mold appears on the surface or fruit of your vinegar--this sometimes happens and I don't know the reason--toss it out and start over.
This is real easy--just let a jar of fresh apple cider sit on the counter (cheesecloth on top). Within a week, you'll have "hard cider"; and a few weeks later, you'll have cider vinegar.
starting rhubarb vinegar from the ends I cut off the stalks