Add all dry ingredients into the jar and shake to mix well. (See video.)
Fill the jar with water leaving approximately 2 inches of headspace from the rim of the jar.
Put a lid on the jar and screw it on tight. Shake the jar vigorously.
Place the jar in a bowl (to catch any spillage), and place it in a warm (room temperature is fine) spot in the kitchen or pantry out of direct sunlight.
Each day, loosen the lid to allow any built-up carbon dioxide gas to escape.
Retighten the lid securely and shake the jar. Place the jar back into the bowl, and return the bowl to a warm spot in the kitchen or pantry out of direct sunlight.
After two days, begin to taste the kvass. You can let the kvass ferment up to 30 days. Once it reaches a flavor that you like, strain out the solids, and decant the liquid into a bottle and refrigerate.
Kvass will stay fresh in your refrigerator for at least six months. It will lose its "fizz" after a few days unless decanted into a swing-top bottle. Take caution if you decide to decant your kvass into a swing-top bottle. Make sure the bottles are specifically made for decanting effervescent beverages. Even under the best conditions, naturally fermented beverages can cause swing-top bottles to break. I do not recommend using them.