Prepare the soaker: combine the Rye Berries, torn pieces of Stale Rye Bread and the Altbrot Soaker in a large bowl; cover with Water so everything is submerged. Let soak at room temperature overnight (or simmer gently 20–30 minutes until berries are plump if you need it sooner), then drain and cool the mixture.
Combine the dry ingredients: in a large mixing bowl whisk together the Whole Rye Flour, Coarse Rye Meal and Sea Salt until evenly distributed.
Add leaven and soaker: fold the Active Rye Sourdough Starter and the Rye Sourdough into the dry mix, then stir in the cooled soaker until you have a very sticky, cohesive rye dough. Add a splash more water if the mixture feels impossibly stiff, but expect a tacky, heavy batter rather than a smooth wheat dough.
Develop structure: using a sturdy spoon or spatula, turn and fold the dough for several minutes to fully hydrate the rye flour and distribute the soaker evenly. The dough will not hold a smooth surface—this is normal for high-rye pumpernickel.
First fermentation: cover the bowl and let the dough rest at room temperature for 2–4 hours until it shows slight rise and bubbles. For deeper flavor and better keeping quality, refrigerate overnight for a slow, cool fermentation.
Shape and pan: generously grease or line a long loaf pan. Transfer the dough into the pan and smooth the top with a wet spatula or your hand; press evenly to remove large air pockets. If you like, dust the top with a little extra coarse rye meal.
Long, slow bake: preheat the oven to a low temperature (about 225–250°F / 110–120°C). Cover the pan tightly with foil and bake for 4–6 hours until the loaf is deeply colored, fragrant, and a long skewer inserted near the center comes out warm and set. For a firmer crust and darker color, remove the foil for the last 30–60 minutes of baking.
Cool and rest: remove the loaf from the oven and let it cool in the pan for about an hour, then turn it out onto a rack to cool completely. For best slicing and flavor development, wait at least 12–24 hours before cutting into the loaf.
