Usually in the summer I think about sourdough more. More bacteria floating around, more active microbes filling my kitchen with their unique "flora" and growing on top of my sauerkraut crock. Hot weather just makes me think of microbes and controlled spoilage, albeit that's not exactly a Norman Rockwell image of an American summer. Anyway, I've made my own sourdough starters from all kinds of things, boiled potatoes, organic grapes, etc. But in Beyond Nose to Tail, they have a recipe for the St. John's Restaurant sourdough starter, which uses chopped rhubarb.
Truth be told, this has also been my most successful starter to date. But that may also be due to the fact that I've been very, very diligent with this starter, since I've been so curious how it would turn out. So perhaps it's the ingredients, but it also might be my method (or at least being consistent with my method). For those who think the proof's in the pudding, below is a super-sour and earthy loaf of buckwheat bread I made last night. It's got a serious tang to it, although using 50% buckwheat and 50% bread flour did make for a bit of a stumpy looking loaf.