In a small saucepan, bring 1/4 cup of water to a simmer. Add the raisins, remove from heat, cover, and let them plump for at least 10 minutes while you prepare the dough. Drain well before adding to the dough.

In a large mixing bowl, combine 1/2 cup warm water, yeast, and granulated sugar. Let sit for 5 minutes until foamy. Stir in 1/2 cup dark rye flour until combined. Cover with plastic wrap and let sit at room temperature for 30 minutes to create a bubbly, active starter.

To the activated starter, add 1 1/2 cups warm water, molasses, cocoa powder, espresso powder (if using), and salt. Stir well to combine. Gradually add the remaining 3 cups dark rye flour and 2 cups of the all-purpose flour, mixing until a shaggy dough forms.

Turn the dough out onto a lightly floured surface (using the remaining 1/2 cup all-purpose flour as needed) or use a stand mixer with a dough hook. Knead for 8-10 minutes (10-12 minutes by hand) until the dough is smooth, elastic, and slightly tacky. This will be a dense, heavy dough due to the rye flour.

Flatten the dough slightly and spread the well-drained raisins over it. Fold the dough over and knead gently for 1-2 minutes until the raisins are evenly distributed throughout the dough.

Lightly grease the large mixing bowl. Place the dough in the bowl, turning once to coat. Cover with plastic wrap or a clean kitchen towel and let rise in a warm place for 2 to 2.5 hours, or until doubled in size.

Gently punch down the dough to release air. Turn it out onto a lightly floured surface. Shape the dough into a tight loaf that fits a 9x5 inch loaf pan. To do this, flatten the dough into a rectangle, fold the longer sides towards the center, then roll it tightly from one end to the other, pinching the seam closed at the bottom.

Lightly grease the 9x5 inch loaf pan. Place the shaped dough into the prepared pan. Cover loosely with plastic wrap or a clean kitchen towel and let rise in a warm place for 1 to 1.5 hours, or until it has nearly doubled and crested over the top of the pan.

Preheat your oven to 375°F (190°C) during the last 20 minutes of the second rise. Bake the bread for 45-55 minutes, or until the internal temperature reaches 200-210°F (93-99°C) and the crust is dark brown and firm. If the crust is browning too quickly, you can loosely tent it with foil during the last 15-20 minutes.

Once baked, immediately remove the bread from the loaf pan and transfer it to a wire cooling rack. Let it cool completely for at least 2 hours before slicing. Slicing warm pumpernickel bread can make it gummy.