Place yeast in a large mixing bowl, add warm water, and stir to dissolve. Add shortening, salt sugar and the all-purpose flour. Beat with an electric mixer at medium speed for two minutes, using a rubber spatula to scrape sides of bowl often. Add whole wheat flour and mix with a spoon until completely blended in, scraping sides of bowl. Cover bowl with a dish towel and place in a warm place (80-85 F) until dough has doubled in size. Beat 25 strokes with a wooden spoon to deflate dough. Spread dough evenly in a well-greased metal loaf pan. The dough will be sticky, so coat your hands slightly with flur and smooth the top of the loaf by patting it with your hands. Cover pan with a dish towel and let the dough rise in a warm place until it's 1/4 inch from the top (about 40 minutes).
Heat oven to 375 F. Bake bread for 45-50 minutes or until top crust is brown and sounds hollow when tapped with a knuckle. Immediately remove bread from pan and brush top with melted butter, if desired. Let cool on cooling rack. Notes: can make white bread using all-purpose flour instead of wheat. In winter, it isn't always easy to find a warm place for the dough to rise. You can heat your electric oven to 100 F and turn it off. Crack the door until the temperature drops about 20 and then put the dough in and close the door.