Combine the rye, pumpernickel, water, starter and malt syrup. Cover and let rest in a warm place (@ 85F) 1 - 2 hours. Should be light and bubbly.
Add remaining ingredients and initiate folding procedure or mix by machine for 10 minutes.
Cover again or place in a plastic container and allow to ferment in a warm location till increased in volume by 25%.
Divide dough and pre-shape. Allow to rest for 20 minutes.
Final shape and sprinkle caraway seeds on top (good side).
Dust bannetons with white rice flour. Place dough good side down into bannetons (caraway seeds will be between basket and dough.
Refrigerate dough for a minimum of 8 hours or up to 2 days.
Preheat oven to 500F. Oven should be well preheated and not used as soon as it reaches 500F.
Remove loaves from refrigerator and invert onto a peel. Shuffle dough into oven and add steam.
Bake loaves for 20 minutes, release steam, and lower temperature to 450. Bake for another 15 minutes or till bread reaches 200F.