I have discovered from Vinegar Man that you can make vinegar out of juice from fruits or grains or roots and even wood as long as it contains sugar or starch.
So, before you throw away any leftover juices, take a look at "Vinegar Types, Methods of Making Vinegars Recipes" on Harvestfields, to see how you can make use of them.
And if you are worried that you will be wasting your time if your homemade vinegar did not turn out well enough for consumption, just spray it in your garden to help get rid of those weeds!
Don't forget to keep the leftover wine (fermented juice) as well. Gang of Pour tells you how in their article "So, Ya Wanna Make Vinegar From Leftover Wine, Eh?". Don't miss their do's and don'ts on the fine art of making vinegar.