I keep a small zip-top bag full of apple cores, peels, and other scraps in my freezer, and I add to it every time I cut an apple for a snack or make a batch of cider. When I have enough to pack into a canning jar, I turn those scraps into vinegar. Essentially, this works by mixing the scraps with water and sugar, letting it ferment, and then ignoring it until the liquid turns into vinegar. The resulting vinegar is slightly less intense and flavorful than “real” vinegar, but still perfectly tasty for making everything from salad dressing to tri-tip marinade.