Dissolve brown sugar in 1 cup hot water. Add shortening, and stir to melt. Let cool.
In a large bowl, dissolve yeast in 4 cups warm water. Add white sugar, salt, and bread flour. Beat well. Stir in shortening mixture. Stir in enough whole wheat flour to make a stiff but not dry dough.
Turn out onto a lightly floured surface. Knead until smooth and elastic. Place in a large, well oiled bowl. Cover, and allow to rise until dough doubles in bulk.
Divide dough into four equal parts. Shape into loaves. Place in greased, 9 x 5 inch pans, turning each loaf over in pan to grease top. Allow to rise until dough doubles in bulk.
Bake at 350 degrees F (175 degrees C) for 35 minutes. Let cool before slicing.
