My preferred flour for this recipe is bread flour mixed with rye. Bread flour is softer and has more protein, which gives a more chewy texture. All-purpose white and whole-wheat flours also work well. Whole wheat, of course, would give the bread an even firmer texture, and a denser loaf and requires more water. So watch the dough and add water if it seems dry. Remember, you want a shaggy dough, not the kind you would normally use to make bread which requires kneading.