At least 5 days before: For the sourdough, mix 40 g flour and 30 ml lukewarm water in a large bowl. The sourdough mixture should have about the consistency of a thick wafer dough.
Close the bowl with a lid or cling film and leave to stand at room temperature for approx. 12 hours. After 12 hours, small bubbles will have formed on the surface of the base and it will have a slightly acidic smell. Stir the mixture briefly once.
After another 12 hours, stir in 40 g flour and 30 ml lukewarm water again. Repeat this alternation of mixing and stirring every 12 hours. For a total of 5 days. The finished sourdough can be stored indefinitely in the refrigerator. It only needs to be fed and cared for again and again.
For the rye sourdough bread, first add salt, then 500 g rye flour in a bowl. Crumble yeast into it. Rub the yeast with your hands and some flour to crumble. Add 450 g sourdough mixture and malt beer. Knead with the dough hooks of the mixer, even easier with the food processor, to a moist, sticky dough. Dust with flour and leave to rise covered in a warm place for about 1 hour. Line a baking tray with baking paper.
Knead the dough briefly on a floured work surface. Shape into an elongated loaf. Place on the baking tray. Cut several times crosswise with a knife. Let it rise again for about 1 hour. Preheat the oven (electric cooker: 225 °C/circulating air: 200 °C/gas see manufacturer). Put bread in the oven. Spray the oven walls with water. Bake the bread for about 15 minutes.
Reduce oven temperature (electric oven: 175 °C/circulating air: 150 °C/gas: see manufacturer) and bake for another 40-45 minutes. With the help of the knock test you can see if the bread is ready: Just knock on the bottom - if it sounds hollow, you can take the bread out and let it cool down on a cake rack.