There was a time, not too long ago, that all breads were sourdough, and that every cook kept a crock of yeasty flour and water bubbling away in her larder. It was fed daily – scraps of dough or more flour and water – and she would dip into the crock, and pull out starter to make breads, biscuits and even old-world sweets like Election Cake. By contrast, granulated commercial baking yeast has only been made available very recently.