Finely grind the wheat and rye grains and mix in the sourdough. Add the cold water and stir everything well, let the sourdough stand overnight.
Bread dough:
Roughly grind the wheat and rye grains, add the ground grain, the salt and the lukewarm water to the finished sourdough mixture, mix everything well and let stand in a warm place for 4 hours.
Grease a bread baking tin and sprinkle with rye or oat flakes, preheat the oven to 180 ° C top and bottom heat, pour the dough into the tins, sprinkle with flakes and bake for about 1.5 hours.
Let the bread ripen for a day if possible before cutting.