I have been experimenting with making whole grain sourdough bread at home. My current recipe is for a loaf that is about 4 cups of flour total, not counting sourdough starter, evenly split between bread flour, whole wheat, and dark rye. After preparation and rising, I cook in a dutch oven, with the dough shaped like a long cylinder stretching from one side of the dutch oven to the other, so that it rises into a loaf shape. Cook time is 30 mins with the lid on, then 5 mins uncovered; at 500 F in a conventional oven. After cook time, I immediately take the loaf out of the dutch oven and let it cool on the counter.
This creates a pretty satisfactory loaf of bread; simple to make, tasty enough, cooked all the way through with a nice crust on the outside. My only issue is that it "burns" on the bottom where the loaf is in contact with the dutch oven. The loaf is slightly blackened on bottom, though that is mostly a cosmetic issue, there is no burnt toast flavor. However, the bottom 1/4 inch of the loaf is very tough and hard to cut when slicing.
I've tried varying cook times and haven't be able to solve this burning problem. What are some tactics that might allow my loaf to cook the same way on the crust and insides, but not burn the bottom as much?