Instructions

1. 1
   Mash the grapes thoroughly and place in a loosely-covered container. Allow to stand at room temperature for 48 hours.
2. 2
   Strain off the fermented juice and discard the pulp.
3. 3
   Add warm water to the juice to make 1 pint (450 ml).
4. 4
   Stir in the flour, and leave at room temperature overnight.
5. 5
   Replenish with 1 pint of warm water and 2 cups of flour daily if the starter is kept at room temperature. If refrigerated, replenish twice a week.
6. 6
   In a glass measuring cup, sprinkle the dry yeast onto the surface of 4 tablespoons of the warm water and allow to stand until it becomes foamy.
7. 7
   In a bowl, combine the rest of the water with the sourdough starter.
8. 8
   Add 1 cup of the flour. Stir until the dough starts to form and then add the yeast mixture. Mix for 5 minutes.
9. 9
   Add the remaining flour and the salt. Knead the dough until it is soft and elastic, 10 minutes or more.
10. 10
    Place the dough in a greased bowl and cover with a damp cloth. Let rise in a warm place (ca. 80°F/27°C to 90°F/32°C) until doubled.
11. 11
    Punch down the dough and shape it into a round loaf. Place the loaf on a greased and cornmeal-dusted sheet pan.
12. 12
    Let the loaf rise in a warm place, covered with a damp cloth, until it has doubled in size.
13. 13
    Brush the loaf with beaten egg white and score the top of the loaf in a criss-cross pattern with a sharp knife.
14. 14
    Bake at 450°F (230°C) with a pan of boiling water under the oven rack for 10 minutes.
15. 15
    Reduce the oven temperature to 375°F (190°C), remove the water and continue baking until the bread is well browned (about 35–45 minutes).
16. 16
    Cool on a rack.