Combine yeast, 1 cup of the warm water and the sugar in a large bowl; stir until the yeast is dissolved. Let stand until mixture is foamy, about 10 minutes.
Stir remaining warm water, the oil and salt into yeast mixture.
Whisk together 7 cups of the all-purpose flour and the whole-wheat flour in a large bowl until combined.
Make a well in the center of the flour mixture. Add half of the yeast liquid to the well; stir into the flour mixture to blend. Stir in the remaining yeast liquid until a rough mass is formed.
Turn dough out on floured surface; this is a very soft dough. Knead until smooth and elastic, about 5 minutes, adding as much of the remaining 1/4 cup all-purpose flour as needed to prevent sticking.
Place dough in lightly oiled bowl; turn dough in bowl so all sides are coated. Cover bowl with towel or lightly greased waxed paper. Let rise in a warm place, away from drafts, for 45 to 50 minutes or until dough doubles in volume.
Grease three 9 x 5 x 3-inch loaf pans.
Punch dough down. Turn out the dough onto a lightly floured surface. Knead lightly. Divide into thirds. Place one portion in each of the prepared pans. Cover with a damp towel or lightly greased waxed paper. Let rise in warm place, away from drafts, until doubled in volume, for 30 to 45 minutes.
To bake, heat oven to 400°F. Bake bread for 25 minutes or until hollow sounding when lightly tapped. Turn loaves out onto wire racks and let cool completely.