Hi Kelvin, while a mature starter can survive quite well in the refrigerator, it's not really thriving in there. Both the wild yeast and Lactic Acid Bacteria (LAB) that populate your starter will benefit from the opportunity to go through a few feeding cycles at room temperature prior to baking your bread. When you feed your starter matters a bit as well. If you feed your starter when it's reached its peak of rising, this tends to favor the yeast, while feeding your starter when it's slightly past its peak is more advantageous to the LAB (which are the primary drivers of flavor development). However, the tricky part of manipulating your starter too heavily in one direction or the other is that you need both the yeast and LAB to function well when it comes time to bake your bread, and yeast and LAB don't always thrive under the same conditions. That's why we emphasize maintaining your starter in a way that builds healthy populations of both the yeast and the LAB. One thing I would recommend is to switch from feeding with bread flour to unbleached all-purpose flour. While feeding your starter with bread flour certainly won't kill it, it will be getting a slightly better meal when you feed it with AP flour. This is because the starch and protein in wheat flour are inversely proportionate; the higher the protein, the lower the starch. Since starch is what your starter consumes and ferments, it will benefit from the higher starch content in AP flour. 

It's during the preferment and dough stages of sourdough bread production that you have the best opportunity to manipulate flavor. For the preferment stage a liquid levain that is slightly past its peak will promote more LAB development. Substituting 10-15% of the white flour called for in the dough portion of the recipe with whole rye or whole wheat flour is also an excellent way to develop more sour flavor in your bread. Refrigerating the dough can also change the flavor profile, but this works best if it is preceded by a fairly warm (75-78F) bulk ferment. 

I hope this helps! Let us know how it goes. 

Barb

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