Fill your mason jar about 1/2 way with grape juice, then top it off with water. Add kefir grains (about 1/4 cup per pint of liquid). You can see how dark the mixture is in the picture above... and how much it has lightened up after 48 hours in the picture below.
When your "champagne" has finished brewing, strain out the kefir grains and bottle the remaining drink in air-tight glass bottles. You can stick this directly in the fridge, as it will be plenty bubbly right out of the jar! As soon as it's chilled, take a sip- delicious!- and I recommend sips, not gulps. :)
Enjoy this probiotic-rich adult beverage with your sweetie and know that you are doing your tummy good!
You can continue using your lovely purple kefir grains for subsequent batches of home-brewed champagne.