Combine rye flour, 3/4 cup all-purpose flour, undissolved yeast, wheat bran, wheat gluten, brown sugar, caraway seed, salt and coffee in a large mixer bowl. Heat water, molasses, vinegar, butter and chocolate until very warm (120°F to 130°F). Beat for 2 minutes on medium speed. Mix in enough reserved flour to make a soft dough that begins to clean the side of the bowl.
Turn out onto floured surface and knead 5 minutes. Cover and let rest 10 minutes. Shape into smooth ball; transfer to a greased baking sheet. Loosely cover dough; let rise 40 minutes, or until almost double in size. Beat egg white and water; brush on surface of bread.
Preheat oven to 400°F. Bake for 35 to 40 minutes. Remove from baking sheet and cool on wire rack.