Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9x5 inch loaf pan.
In a large mixing bowl, combine all-purpose flour, whole wheat flour, baking powder, salt and brown sugar. Pour in beer, stir until a stiff batter is formed. It may be necessary to mix dough with your hands. Scrape dough into prepared loaf pan.
Bake in preheated oven for 50 to 60 minutes, until a toothpick inserted into center of the loaf comes out clean.