I have been baking bread with the Oregon Trail starter for several
months now, but I haven't really figured out how to get my bread to
turn out sour. I've tried letting the sponge sit for 24 hours before
use. I've also tried allowing the dough to rise a full three times
before baking. So far, no luck.

Is it because I'm using only wheat flours? If I convert my starter
over to rye flour, and start making rye breads, will the sourness
likely increase? Any other tips?

Thanks for all help!

Sincerely
Aaron