In a large mixing bowl - the batter will rise so you need some room - add the water and sprinkle in the yeast. Let it stand for 15 minutes until it becomes nice and foamy.
To a small bowl, mix together the rye flour, all-purpose, brown sugar, all-spice and salt. Add the flour mixture, milk and melted butter to the yeast mixture and mix until smooth. Cover the bowl with plastic wrap and let it stand overnight at room temperature.
Just before cooking the waffles, beat in the two eggs and baking soda; stir until well mixed. The batter will be fairly thin with a few lumps. Preheat your waffle iron and be sure to brush it with oil or butter (I had some sticking issues!). Pour about 1/2 cup to 3/4 cup batter into the hot waffle iron. Bake the waffles until they are golden and crisp, or according to the directions of your waffle maker.