Place the beet pieces into a one-quart mason jar. Add the optional ginger.
Add the whey or kraut juice.
Fill the jar to within one inch of the neck with filtered water. Add the sea salt and stir well, to dissolve.
Cover, screwing the lid on loosely to allow gasses to escape. Or use airlock lids to ensure success (and prevent kahm yeast [see notes below in post]; see link below in Recipe Notes). Keep at room temperature and out of direct sunlight for two days in warm weather, or up to 8 days or longer in colder weather. (You may also use a warming mat or yogurt maker to maintain a steady warm temperature.)
After the kvass has deepened in color, has a pleasantly sour flavor, and shows signs of bubbles near the surface, or active effervescence, strain all but ¼ cup from the mason jar into a blender.
Add strawberries and optional stevia/maple syrup or honey. Blend 30 seconds.
You can serve the kvass now, but preferably continue a slow, gentle fermentation in the fridge. Transfer Strawberry Beet Kvass into a 4-cup mason jar and a 2-cup mason jar. Chill and store kvass in fridge, allowing it to continue to ferment, for up to 7 days. Serve.
If you'd like to make another batch of kvass, the same beets can do one more round (with the reserved 1/4 cup kvass): Simply add water to the fill line again. Add 1/4 teaspoon sea salt. Stir to dissolve.
Again, keep the mixture at room temperature for 2-8 days minimum. After the second batch, the beets are now “exhausted” and can be composted; but ¼ cup of the strained kvass may again be used for another batch in place of whey.