Dissolve yeast in warm water in a large mixing bowl, stirring well. Let stand 5 minutes or until bubbly. Stir in shortening and salt. Add 6 cups flour alternately with 2 cups water, beginning and ending with flour. Gradually stir in enough remaining flour to make a soft dough. Shape into a ball.
Place dough in a 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; turn out onto a lightly floured surface. Knead 6 minutes or until smooth and elastic. Cover and let dough rest 10 minutes.
Divide dough in half, and shape each into a loaf. Place in 2 greased 8 1/2- x 4 1/2- x 3-inch loaf pans. Cover and repeat rising procedure 20 minutes. Cut 2 diagonal slashes, 3/4-inch deep, in top of each loaf. Bake at 400° for 50 minutes or until loaves sound hollow when tapped. Remove bread from pans immediately; cool on wire racks.