Just because you cannot drink your champagne DOES NOT mean you cannot use your champagne.
You can use the half used wine to make wine “champagne” vinegar!
-Apple cider vinegar (home made or store bought)
1. Measure the wine and pour it into a wide-mouth glass or ceramic jar or bowl. Add 1/3 cup live vinegar to vessel for every 1 cup wine. Cover the container with a double layer of cheesecloth (to maintain airflow while keeping bugs out), secure it with a rubber band, and leave it in an out-of-the-way, room temperature place.
2. After a week or two, you’ll notice a skin or film forming on the surface. That’s the mother, and it shouldn’t be disturbed. You’ll want to taste the mixture every so often to see how the process is going. (Do so by gently nudging the mother aside with your tasting spoon or a chopstick, taking care not to jostle it so much that it sinks to the bottom, or you’ll start the waiting process all over again). If you started with the equivalent of a glass or two, you can start checking around the 3 week mark. If you started with a full bottle, wait until. At least a month and a half have passed. Keep tasting until it tastes like vinegar, and don’t give up- it could take 2 or 3 months.
3. Once the mixture tastes nice and tart, discard the mother (or transfer it to a fresh jar to make a new batch of vinegar with more leftover), and store the vinegar in jars with airtight lids. (Exposure to air is essential for the fermentation part, but is no longer a good thing once your wine has turned into vinegar.) Store it in a cool, dark place. Vinegar has an indefinite shelf life and will probably taste even better after it has aged.