Preheat the oven to 325 degrees F (165 degrees C). Dissolve yeast in warm water until foamy, about 10 minutes.

In a large bowl, stir together the all-purpose, whole wheat, and rye flours with the bulgur, cornmeal and powdered milk. Stir in the yeast mixture, salt and chicken broth to form a stiff dough. Add more broth if necessary to hold dough together. Roll dough out to 1/4 inch thickness on a lightly floured surface. Cut into desired shapes using a cookie cutter. Place biscuits 1 inch apart onto an ungreased cookie sheet. Combine the egg and milk; brush onto the tops of the biscuits.

Bake in the preheated oven for 45 minutes, then turn off the oven and let the biscuits sit in the closed oven overnight to become extra hard and crunchy.