I'm pretty new to baking sourdough bread, and one of the most appealing things about sourdough baking to me is being able to get a really sour loaf. I've been trying to play around with my basic recipe (using different levels of sourness in the starter and different bulk fermentation lengths) to maximize the sourness of my final loaf. In my limited experience, it seems like my sourest was one where I left the dough to bulk ferment for about 24 hours.
What has helped everyone else get a really sour loaf?