Choose a tall glass with sides that are as vertical as possible. In this glass, stir together the active dry yeast, sugar and warm water. Once sugar is dissolved, set aside until foamy and activated, 5-10 minutes.
In a medium pot, bring all "Liquid Ingredients" to a light simmer, just until the shortening dissolves. Remove from heat, and let cool completely.
In a large mixing bowl, combine yeast mixture, cooled Liquid Ingredients, and rye flour until just incorporated.
With a wooden spoon or by hand, begin mixing in the all-purpose flour. You will need 6-7 cups, depending on factors such as local humidity. You will know you are done when the dough is no longer sticky and retains its shape.
Lightly flour a flat surface. Knead dough for 10 or so minutes- you'll be tired! Your dough is done when it springs back after being punched.
Grease a large bowl with shortening and place your dough in it to rise. Cover with a quilt or very heavy towel. Let rise in a warm area until doubled in size, about 2.5 - 3 hours. (Possibly longer if you live at high altitude like me!)
Grease 3 loaf pans with shortening. Cut dough into 3 equal pieces and shape to fit in pans, making sure to knead when necessary to eliminate air pockets.
Let rise, covered with the same quilt, until more than doubled in size. You want it rising above the loaf pans! This will take another 2-3 hours.
Preheat oven to 375 degrees F (190 C). Bake loaves for 45 minutes.
Immediately remove bread from loaf pans once they're done baking. Rub each side of each loaf with butter and let cool.