Dissolve yeast in 1 cup warm water in a large bowl, and let stand 5 minutes. Stir in 1 cup all-purpose flour and 1 cup whole-wheat flour. Cover and let stand for at least 5 hours or overnight.
Combine yeast mixture and 1 1/3 cups water using the paddle attachment of an electric mixer. Switch to the dough hook attachment, and slowly add remaining all-purpose and whole-wheat flour. Knead with dough hook 10 minutes. Add salt, and continue to knead 5 minutes or until smooth.
Place dough in a very large, lightly greased bowl, turning to coat top. Cover and let rise in a warm place (85°), free from drafts, 2 hours or until tripled in bulk.
Turn dough out onto a lightly floured surface; knead by hand to form a tight ball. Return dough to lightly greased bowl. Cover and let rise in a warm place (85°), free from drafts, 45 minutes or until doubled in bulk.
Place a baking stone on oven rack in oven, and preheat to 450°. Slide rack out of oven, and place dough on baking stone. Score the top of the dough 2 or 3 times with a sharp knife, and slide rack back into oven. Spray dough with water to create steam. Bake 25 minutes; reduce heat to 400°. Bake an additional 10 to 15 minutes or until bread sounds hollow when tapped.