Porttequilamaplevinegars
Nice history and how-to at Popular Science on making vinegar at home

Vinegar is one of those ingredients that people don’t think of as often as they should. It is mostly just seen in salad dressings and pickles, which is a shame, because there is a whole world of flavor there just waiting to be tapped into. There are often times, especially during the holidays, when there is leftover wine after a festive dinner. Many of us will cork the bottle, with or without various safeguards to preserve the contents, and set it aside for the next day. Occasionally the bottles are forgotten, and when you finally open them again you find that the wine has evolved into something quite a bit different from what you were expecting. In these moments the change is often viewed with disappointment, as a delicate beverage has transformed into something sharper and edgier. Frankly, though, a smart cook will see the change as an opportunity. Good wine makes good vinegar and good vinegar is a stellar cooking ingredient.