I have been using all white bread flour in my starter for its entire month-long life. It seems to be thriving and healthy. That said, my bakes and levain builds are now including a higher concentration of whole wheat flour (typically 20%). Is there a problem or any reason not to change my mother starter to a combo of whole wheat and bread flour?
That’s absolutely no problem.
It wil get a little bit stiffer but with only 20% WW not very much.
I change what I feed my starter all the time hah. No need to fret about it. Every variable does count, and will change how the starter behaves, buuuuut hey, it’s not gonna hurt the starter.
You might have to adjust your fermentation times if you start feeding WW (it’ll go faster). To compensate, you might lower the inoculation or keep it at a lower temp