The day before, in a bowl, stir together ingredients for the starter. This is called refreshing the starter.
Cover your bowl with a plate or plastic wrap and let sit at room temperature for 12-16 hours. (The dough likes it warm. Temperature should be above 20°C) Your dough should look bubbly and have doubled in size. It should also smell sour.
The next day add remaining ingredients for the bread dough.
Knead the dough for one minute. It will be rather sticky (especially because of the rye flour) and rather soft. Cover and let rest for 10 minutes. This will help to absorb the water properly and develop the gluten. Knead again for one minute. You will probably note that the consistency has changed and that the dough feels a little bit firmer. But it still will be rather soft.
Line a loaf pan with parchment paper. (Sourdough can be a little hard on your pans. That’s why you shouldn’t grease the pan but use some parchment instead.) Transfer the dough to the pan. Use wet hands and slightly press to shape it a bit. Cover with a damp kitchen towel. Preheat the oven to 220°C (425°F). Let the dough rise until doubled in size. This will take 1-2 hours depending of your starter, the room temperature, etc.
Bake for ten minutes. Lower the temperature to 200°C (400°F). Bake for 30 more minutes or until a toothpick inserted comes out clean. (Even better if have a meat thermometer – it will finally be useful – you can insert into the loaf. The temperature should be 93°C (200°F).
Let the loaf cool completely before slicing. You can also wait a whole day to cut this bread, this will improve the flavour.