Wheat or Rye or Oat starters
I used to believe that any sourdough starter could raise a variety of other grains in a recipe but I now believe each starter is specific to itself and it's pH. If you want a mixed starter, one for say wheat and rye, then combine two starters first, then feed with mixed flours.
I also think the liquid that forms on top of the starter is the "sour" and should be used. I poured it off once and noticed a big reduction in sour taste. :) Mini Oven