elwolf101's Comments

You're correct that there are bacterial processes going on in sourdough.  However, the bacteria (usually lactobacillus) are involved in a symbiotic relationship with the yeasts.  They actually feed on the metabolic waste from the yeast.  Without yeast the bacteria don't have a food source.  I believe the bacteria produce the sour flavor (*their* metabolic contribution) while the yeasts provide the leavening.

San Francisco produces some of the most flavorful sourdoughs you can get.  Other moist climates produce great sourdoughs too.  This is because of the particular strain of wild yeasts present in those locations.  I live in a very dry location and my sourdoughs are very so-so in flavor.  I could order some San Francisco sourdough starter and that would be great--for awhile--but eventually my local wild yeasts would bump out the exotic San Francisco yeasts and I'd be back to my bland sourdough again (unless I kept ordering more).