My 8th bread is also turned out good, I followed the same process and could replicate the result.
I think I can share with Bernd how to bake a sourdough bread.

Sourdough is a culture of bacteria and yeast fed on flour and water. As the result of their digestive process - with the help of oxygen - they create bubbles in the dough when added to it, making the pastry lighter. Without them we could only eat flatbreads, which ofc also have their place in cuisine.
How to make sourdough?
I did not make one, but in theory the process looks like this:
In a jar mix flour and water, 50 grams each. Next day discard half of it, add 50 grams of both again to what's left. Next day discard the half of this too, add 50 grams of both again. And again, and again for 10 days. By this time you should have sourdough. This should be bubbly, taste sour (kinda beer taste), and have a vinegary sour smell.
I bet in the old days, and maybe even in our age, some used saliva to kick start the process with the bacteria found in our mouth, which digest the carbohydrates we consume the same. I think I read something about the fermentation of horse milk into kumis, that they do this. Or somewhere else, never mind that.
So now that we have sourdough, lets mek the breda.