I've been making bread for awhile now without incident (with the world's easiest base recipe). I thought it would be a simple extension to establish a starter culture in lieu of relying on commercial yeast.
All over the Internet, it's stated that all you need to do is set out equal parts flour and water and natural yeast will colonize and froth it up - or you can dope it with bread yeast, or inoculate it with likely-colonized dried fruit (I did all this and also added some drops of dregs from wine and beer bottles).
Set out, and every day or so, dump half of it and replace with fresh water and flour to keep the happy fungi growing actively. I've spent half my professional life inside a sterile hood, culturing fungi, so this seemed pretty trivial. But it didn't work. Here is fresh dough mixed with a full cup of starter "culture" that smells faintly right but never rose. Any ideas what went wrong?