Depth of Flavor question
I've been making sourdough bread for awhile. I think I may be at the end of the beginner's stage, as I know how to do the basics, including: how to use starter at various room temperatures, or chilled, or fresh, or not refreshed, or aged; how to use starter to build levains, and pre-ferments; how to use white flours, and whole grain flours, and grains, and combinations of same; how to retard dough at various times and temperatures, or using warmer temperatures; how to use different hydration percentages; how to build dough in stages, and so on. I preface my question this way to not come off as a novice, but, also, to not come off like I think I've tried everything. Somewhere I read something like this: "anyone can make good bread; we want to make GREAT bread." So, that's me. I can make OK to good bread. I think I could make great bread, or at least bump it up to a consistently "really good bread" level.
My question: At this stage of what I (think I ) know about how to bake sourdough bread, I think the breads I bake should have more depth of flavor, and I am not referring to sour. I have cultured three different starters. The first, I used fermented raisin water which was not what I wanted. The starter worked fine, but the bread lacked flavor. The second starter was cultured using the Debra Wink method. The first time I used it, the bread was wonderful. REALLY good. One of my best. The second time I used it, the bread had about half the flavor. I did not change any ingredients or technique(s) that I know of, but something happened (did not happen). Most of the loaves that followed using the second starter were OK. They tasted OK to good. Nothing great. After trying a variety of techniques, methods I read about from many sources including Hamelman, Reinhart, and Richardson, and this and other sites, nothing much seemed to change. The bread was good, but not REALLY good. So, I cultured a third starter thinking maybe my first starter contaminated the second starter. Before culturing the third starter, I sterilized all of my utensils and containers and used bottled water. I was attempting to avoid any contamination from the other two starters. The flour I used was KA AP. It took longer than I expected, but when it was ready, and I used it, the result was disappointing. I do understand about young starters, but that was about six months ago, and there still is not really any discernible change. The bread is good, but I still think it should have more depth of flavor. At this point, I will add, that on occasion, when all of the planets were in the correct alignment (so to speak), I would occasionally produce a loaf that landed somewhere between good and really good. When I would attempt to replicate all of the techniques using the same ingredients, the result was not as good. So . . . , what is it?
Any suggestions would be appreciated.