Thermonuclear cloud

So I’ve been trying to recreate the German sourdough rye of my childhood. I’ve got the flavor profile down but when I bake the loaf looks like a thermonuclear mushroom cloud.  Recipe is 1 part dark rye sour to 4 parts AP wheat flour with a tablespoon of oil and molasses and a 1/2 teaspoon of salt. 1 packet dry yeast.  No added water unless the dough is too dry. (Sour is the consistency of pancake batter).   Bake at 400 DEG F for 40 minutes. 

I’m kneading the dough for 15 minutes by hand and get a nice soft dough. I proof for an hour (70 DEG F) covered and then punch down and form the boule. This goes on a baking sheet with some flour and I invert a large bowl over everything to keep moist and allow to rise for an hour.