I have a beloved sourdough started from yeast and bacteria captured in southeast Michigan. I usually store and feed it as a liquid (equal weights flour and water) and convert what I need into a stiff starter two days before baking. I’ve had very good luck with most of the Bread Bible sourdough recipes and with replacing 30-40% of regular bread recipes with my starter. I’m very happy with the rise, crust, crumb, and flavor of my breads, but it is a very rare that any of them taste appreciably sour. Does anyone have any recommendations for coaxing some significant sourness out of a mild-mannered starter?