Dear Ralf,
You cannot set the temperature yourself, but the appliance has 4 preset programmes with different temperatures:
Natural yoghurt (42 °C), yoghurt, vegan/lactose-free (38 °C), fresh cheese (30 °C}, herb extract (55 °C).
If 30° is also possible, you can use the fresh cheese programme to cultivate your sourdough culture.
(the Rommelsbacher data sheet explicitly mentions the possibility of making sourdough, see below).

https://www.rommelsbacher.de/media...

Hi Ralf, Rommelsbacher describes how to do this on its own blog:
https://rommelsbacher.blog/2019...