Bread is a good tool for practice. It's concise and measured, though sometimes one bread you previously made turns out slightly different. Here's a case in point; Berliner Kurzsauer. I've made it several times and I always go back to this formula. Why? Well, it's good when you're short of time and jonesing for some good old Berliner brot!
This time, my sauer was sluggish. So I left it several more hours and proceeded as usual through the rest of the formula with fantastic results. It's a bread that lasted a few extra days!