Sourdough Whole Wheat, Super Sour Molasses Flavor

Today I baked up the Whole Wheat bread recipe in Hamelman's book using White Wheat instead of bread flour, and Wildflower Honey. (A bit more than the recipe called for, a little less than double) then let it proof in the fridge for 48 hours.  I got a super-sour loaf that was a bit dense with no real oven rise.  Still, the flavor is great, with a touch of molasses.  Yum.  Anyone else played with retarding for extended times to get really sour breads?