Place the beets in a 2 quart glass or ceramic pitcher. Cover with filtered water and stir in the sea salt. Cover with a clean cloth and place in a dark cool place for 3 days. After 3 days, remove the beets and store the kvass in the fridge (if there is foam on the top, just skim it off). It will keep for about 2 weeks.
Note: It is important to chop the beets and not grate them. Grated beets will create too much juice and will ferment too rapidly, resulting in alcohol instead of lactic acid.