Traditional pumpernickel from Westfalia spent many hours in a cooling down bread oven to obtain its characteristic dark brown color. This very long low-temperature baking is the essence of pumpernickel.
Mix the ingredients of the starter dough in a large non-reactive bowl, cover with cling film and let it sit for 5-6 hours. Prepare the scalded rye at once. Put the ground rye into a second bowl and pour boiling water over it. Cover with a lid, let it cool for 5-6 hours.
Mix the scalded rye into the starter dough, cover with cling film and leave to ferment for another 5-6 hours.
Add all of the remaining ingredients to the large bowl and mix briefly with a wooden spoon until the dough comes together. Cover with cling film and let it rest for 20 minutes.
Oil the interior of a large non-reactive loaf tin (mine is 12x30cm) and dust it with wholemeal flour. Stir the dough briefly and spoon it into the the tin, gently pressing it down. Even the surface out with a spatula, cover and let it rise.
When the dough is almost double the size preheat the oven to 180°C (no fan). Cut a sheet of parchment paper so it fits the lenght of the loaf tin and use it to cover the surface of the pumpernickel. Then wrap the whole tin tightly with aluminium foil.
Put the bread into the oven, bake for 5 minutes. Reduce the temperature to 120°C and bake for 8 hours. Turn off the oven without opening it, leave the bread inside for additional 2 hours.
Unwrap the foil, let the bread cool in the loaf tin for 5 minutes. Carefully tip onto the cooling rack. Wait 12 hours before slicing.