Step 1

Bring the water, sugar and seasonings/raisins (if using) to a boil. Stir to dissolve the sweetener, and then turn off the heat. Allow the mixture to cool to somewhere between 70 and 90 degrees (luke warm).

Step 2

Chop the bread and toast it until it resembles slightly overdone toast (browned but not burned).

Step 3

Place the toasted bread and sourdough starter in a half gallon mason jar and pour the warm liquid over the bread (ensuring that it's no more than 90 degrees to avoid killing the cultures). Add additional water if needed to fill the jar to within an inch of the top.

Step 4

Cap the jar loosely and allow it to ferment at room temperature for 2 to 7 days.

Step 5

Test the mixture, and when it's cultured to your taste, filter through a fine mesh strainer.

Step 6

Bottle the kvass in mason jars or Grolsch bottles and store in the fridge. Drink within 7 to 10 days, this beverage does not withstand extended storage.