Dissolve yeast in warm water, let stand 5 minutes.
Combine shortening, butter, milk, sugar, and salt in a large mixing bowl, mix well.
Cool to 105° to 115°.
Add yeast mixture and 1 cup flour, mixing well.
Gradually stir in enough remaining flour to make a slightly stiff dough.
Turn dough out onto a floured surface, and knead until smooth and elastic (about 8 to 10 minutes).
Place in a well-greased bowl, turning to grease top.
Cover and let rise in a warm place (85°), free from drafts, 1 1/2 hours or until doubled in bulk.
Punch dough down, and divide in half; shape each half into a loaf.
Place in two well-greased 8 x 4 x 3-inch loaf-pans.
Cover and let rise in a warm place (85°), free from drafts, 50 to 60 minutes or until doubled in bulk.
Bake at 350° for 25 to 30 minutes or until loaves sound hollow when tapped.