Boil a kettle of water; allow to cool slightly.
Combine sugar with 2 cups of hot water, and mix until sugar dissolves completely.
Place bread chunks into a half-gallon jar, and pour sugar water over the bread.
Fill the jar with the hot water just above the curve. Close tightly.
Allow to sit at room temperature for up to 7 days, burping daily, to allow pressure to escape.
Once the liquid tastes tart and pleasant to you, strain the bread.
For more carbonation, add several raisins after the bread is strained, close the jar airtight, and allow to ferment at room temperature for one or two more days.
Chill before serving.
