Combine yeast, 1/2 cup warm water, and sugar in a 2-cup glass measuring cup; let stand 5 minutes.
Beat yeast mixture, 1 1/2 cups whole wheat flour, and next 4 ingredients at medium speed with an electric mixer until blended. Stir in remaining 1 1/2 cups wheat flour. Add bread flour, 1 cup at a time, beating after each addition. Let stand 15 minutes.
Turn dough out onto a lightly floured surface, and knead 5 to 10 minutes or until smooth and elastic. Place in a well-greased bowl, turning to grease top.
Cover and let rise in a warm place (85°), free from drafts, 1 hour or until doubled in bulk. Punch dough down, and divide into 2 equal portions. Shape each portion into a loaf; place loaves into 2 greased 9- x 5-inch loafpans.
Cover and let rise in a warm place, free from drafts, 30 to 45 minutes or until doubled in bulk.
Bake at 375° for 20 minutes; cover loosely with aluminum foil, and bake 15 more minutes or until loaves sound hollow when tapped. Remove from pans, and cool on wire racks.