Fermented Grape Soda

Directions

1. 1
   Stir 1 teaspoon ginger, 1 teaspoon sugar, and 4 cups water in a 32-ounce canning jar to combine. Cover jar with cheesecloth; secure with a canning jar band (without lid). Let sit 1 day out of direct sunlight at room temperature.
2. 2
   Stir in 1 teaspoon ginger and 1 teaspoon sugar and let sit 1 day. Repeat twice more. Mixture (ginger bug) should have bubbles throughout and release more when agitated.
3. 3
   After 3 days, puree grapes in a blender until smooth. Strain, pressing on solids (you should have about 4 cups juice).
4. 4
   Combine juice and 1/2 cup ginger bug in a large nonreactive bowl. Cover with cheesecloth; secure with a large rubber band. Let sit out of direct sunlight at room temperature, skimming white mold from surface, until mixture is slightly foamy and releases bubbles when stirred, 3-4 days. Strain into bottle, cap, and let sit at room temperature until bottle feels pressurized, about 1 day longer. Chill.
5. 5
   DO AHEAD: