Why bother making your own wine vinegar? Because you can. To be clear, if you find yourself with leftover wine, you could also drink it or cook with it, but waiting it out until it turns into something salad-worthy is an experiment worth trying at least once. That is to say, homemade vinegar is not the most practical use for excess wine—it’s something you do for love of the game. It’s far easier to buy artisan vinegar than to buy a good bottle of wine and let it go sour. But who can resist playing god with millions of microscopic bacteria when the opportunity presents itself? And think of all the fancy things you’ll be able to make once you have extra-fancy vinegar, like pickled garlic to serve on crostini with expensive cheese, or luxurious bernaise sauce that you can slather atop a thick grilled porterhouse steak. Now that you have the idea of making your own vinegar, you won’t be able to shake it.
Wine turns into vinegar when its alcohol is transformed into acetic acid. When wine is left uncorked and exposed to the elements, it will eventually attract wild bacteria—namely acetobacter aceti—that can be found floating in the air around us, no matter where on earth you are. Additionally, as a fermented product, wine already contains plenty of acetic bacteria, but as long as these bacteria aren’t exposed to oxygen (like in a tightly sealed bottle), they remain in a dormant state. But once oxygen shows up to party, those bacteria wake right back up and dive straightaway into an epic bender, devouring any alcohol molecules they come across, eventually turning the wine into vinegar.
To make wine vinegar the easy, old-fashioned way, pour your wine, either red or white, into a wide-mouthed jar. Cover with a piece of cheesecloth (to prevent fruit flies) and secure with a rubber band, then put it somewhere warm; bacteria like doing their thing between 42 and 115 degrees Fahrenheit, and the warmer, the better. Next, forget about it for a while. Let nature take its course for about six weeks, then check in on your vinegar and give it a little taste. If you like it, pour the wine vinegar into a bottle, seal it up, and go have fun with it. If six weeks wasn’t enough time for the wine to go sour, just let it ride, giving it a taste once a week until you’re happy with it.
If you can’t wait around forever for wild acetic acid bacteria to set up shop in your jar of abandoned wine, you can speed up the process by using something known as a vinegar mother. Though it looks rather dubious and “spoiled,” a vinegar mother is perfectly safe: it’s a natural film of cellulose created by the bacteria that looks like a jiggly-wiggly raft of goo that will float on top of your wine. You can buy full-grown vinegar mothers online or at a local home brew shop, but you can also grow your own by spiking your wine with a live vinegar containing active cultures, a product you can readily find in most supermarkets—the bottle’s label will specify that it contains the mother.
In a glass jar, combine the live vinegar with the red wine of your choice in a 1:4 ratio, then cover with cheesecloth and a rubber band. Allow to sit in a warm space for about two weeks, give it a taste to see how the process is going, then continue to let it age until it converts to a pungent, flavorful wine vinegar that makes you happy. Once done, pour the vinegar through a strainer into a clean bottle, then use any collected bits of mother to make even more vinegar. Soon enough, trillions of acetic bacteria will be writing creation myths about you, and that tastes just as good as any salad.