I'll be making Kimchi soon, but I had read about making fermented soda, starting with something called a ginger bug. You take ginger, preferably organic, grate it, toss it in a jar with some water, preferably filtered, and some sugar. You add a little more ginger, water and sugar every couple of days until its bubbling away. See, the ginger, like many other vegetables, has a natural bacteria on it that in the right conditions, help ferment the ginger.
Once the fermentation process is underway, you can then take a half gallon of fruit juice, place it in a jar with a half cup of strained ginger bug juice and top the jar with a cloth to help it breathe. After about a day or two, you can bottle the fermented liquid into proper bottles for carbonated beverages (or else it could explode) let sit for another day or two at room temp, and then refrigerate. After it gets cold, open the bottle, over the sink in case its incredibly fizzy, and enjoy. One thing to remember, the longer it sits, the more chance it has to become alcoholic. As the bacteria eat the sugar, the end products are carbon dioxide, making it fizzy, and alcohol. But please be careful, because if it sits too long, it could just go bad, so don't try to turn fruit juice into some crazy alcohol experiment.
So, after my ginger bug bubbled away for a few days, I added it to some mango juice to create a lovely mango soda that may or may not have given me a slight buzz (real slight). It has a nice fizz, without being overly bubbly, something I don't like in soda. I actually stopped drinking soda a long time ago, as there's nothing in soda that's good for you and so much that's bad. A natural, homemade soda during the summer is very refreshing.
Side note- a few weeks after I originally wrote this, my original ginger bug did eventually go bad. It grew mold (blech), and became rancid. So, for future batched, consume more quickly!