Place the quartered beets, garlic, ginger, optional lemon juice, and optional dash of completed beet kvass in a clean glass vessel sized to the batch.
Choose one salting method: add the measured dry mineral salt and fill with filtered water, OR prepare a separate 2 percent mineral-salt brine by water weight and fill with that. Do not combine methods.
Set a clean fermentation weight over the beet, garlic, and ginger so every solid remains below the liquid.
Fit a pressure-aware airlock or self-venting closure and ferment at room temperature out of direct sunlight.
Begin checking around day 3 and continue through the 7-to-10-day window until the kvass tastes pleasantly tart.
Remove the weight, strain through a securely nested fine stainless strainer, transfer to a clean glass jar, cover, and refrigerate.