Prepare the Doughs (Autolyse): In two separate bowls, mix the ingredients for the Light Rye and Dark Pumpernickel respectively, excluding the salt. Mix just until no dry flour remains. Cover and let rest (autolyse) for 45–60 minutes.

Add Salt and Knead: Add 8g of salt to each bowl. Knead each dough (separately) for about 5–10 minutes until smooth, or perform 4 sets of stretch-and-folds over the first 2 hours.

Bulk Fermentation: Cover both bowls and let them rise at room temperature (70-75°F) for 4–6 hours, or until they have increased in volume by about 50–75% and look bubbly.

Shape and Swirl: Turn both doughs out onto a lightly floured surface. Roll each dough into a rectangle, approximately 8x12 inches. Place the dark dough directly on top of the light dough. Roll up tightly, jelly-roll fashion, starting from the short end to form a loaf. Pinch the seam to seal.

Final Proof: Place the loaf into a greased banneton or a 9x5 inch loaf pan. Cover and let rise for 1–2 hours at room temperature, or cold-proof in the fridge for 8–12 hours.

Bake: Preheat oven to 425°F (220°C) with a Dutch oven inside. Score the top of the loaf. Place in the Dutch oven, cover with lid, and bake for 30 minutes. Remove the lid, reduce heat to 400°F (200°C), and bake for another 15–20 minutes until the internal temperature reaches 205-210°F.

Cool: Let the bread cool completely on a wire rack for at least 2 hours before slicing to ensure a perfect, non-gummy crumb.