Activate the yeast: In a small bowl, combine warm water and yeast. Let it sit for 5-10 minutes until foamy.
Mix the dry ingredients: In a large mixing bowl, combine rye flour, bread flour, cocoa powder, caraway seeds, and salt.
Combine wet ingredients: Add the molasses, apple cider vinegar, and vegetable oil to the yeast mixture. Stir well.
Form the dough: Gradually add the wet mixture to the dry ingredients, mixing until a dough forms. Knead the dough on a floured surface for 8-10 minutes until smooth and elastic.
First rise: Place the dough in a greased bowl, cover with a damp cloth, and let it rise in a warm spot for 1-1.5 hours or until doubled in size.
Shape the loaf: Punch down the dough and shape it into a loaf. Place it in a greased loaf pan or shape it free-form on a baking sheet.
Second rise: Cover and let the dough rise again for 30 minutes
Bake: Preheat the oven to 375°F (190°C). Bake the bread for 35-40 minutes until the crust is firm and the bread sounds hollow when tapped.
Cool: Remove from the oven and let the bread cool on a wire rack before slicing.