Preheat the oven 400 degrees F.

In a large mixing bowl combine the whole wheat flour, rye flour, brown sugar, baking soda and salt. Add the buttermilk and 1 cup of beer. Stir until the dough comes together into a ball. If the dough seems too dry add a splash more of beer. The dough should be slightly sticky.

Turn the dough out onto a floured surface and kneed into a rough ball or football shape. Place the dough on the prepared baking sheet. Sprinkle with a little flour and use a sharp knife to score a cross on the top of the dough.

Bake for 40-50 minutes, until the loaf has almost doubled in size and sounds hollow when tapped. Allow to cool a few minutes, slice and serve. Bread can be reheated or used for morning toast.