I'm sure that this question must already have been answered many times on this forum, but I can't seem to find it.  If it's easier, please just point me in the right direction! :)

I've been working with my wild yeast sourdough starter for a few months now, and I just love it.  I would now like to try my hand at using it in recipes that call for commercial yeast -- a sort of substitution.  Partly for frugality, partly for fun, and partly for health (so far so good in my immediate family, but diabetes has hit some of my older relatives and so the discussions posted here about sourdough & blood sugar have got me thinking.)

I'm just not sure how to go about it.  I assume that at some point I would need to calculate in baker's percentages the weight of flour and water in my starter and subtract that and the yeast from the commercial yeast recipe.  But what about other ingredients from that recipe -- when should they be added?  Do I first create a firm starter from my sourdough culture and once that has doubled, do the math and add in the other ingredients, before the first rise (of the recipe)?  Also, other than the lengthened rise times, is there anything else that I should be taking into account?

Thanks!

Karen

Does vegetable oil work as a substitute for butter in baking yeast breads? I use it (or applesauce) in baking other stuff. I don't have access to butter or shortening.