First make the sourdough.
First day: Mix 100 g of rye flour with 100 ml of warm water, cover and let stand.
Second day: add 100 g of rye flour and 100 ml of warm water, mix well and let stand again covered.
Third day: add 200 g of rye flour and 200 ml of warm water, mix well and let stand covered.
On the fourth day, the sourdough can be processed:
Knead the sourdough with all the other ingredients until it is no longer sticky. Let rise in a covered bowl for 20 minutes. Knead again and then place in a bread pan.
Put the mold in the oven, let it rise again at 50 °C with the door slightly open (clamp a cooking spoon between them).
Remove the pan, cover with kitchen towels, preheat the oven to 170 °C, then bake for 50 minutes. Watch for browning, take out earlier if necessary.