1Combine rye flour, beer, and yeast in a large bowl. Cover bowl with plastic wrap. Set out overnight. Do not refrigerate.
2The next day, add sugar, salt, shortening, and egg; beat with mixer until smooth. Stir in caraway seeds, if wanted. Add enough white bread flour to make a soft dough.
3Knead on a lightly floured surface until smooth, approximately 10 minutes. Place in a greased bowl, and turn to oil the surface of the dough. Let rise in warm place about 1 hour, or until doubled.
4Punch down dough, and divide in half. Shape into round or oblong loaves, and place on greased baking sheets sprinkled with corn meal. Let rise for 30 minutes.
5Bake at 400 degrees F (205 degrees C) for 30 minutes. Cool on racks.