A slow-fermented rye starter gives the bread its signature earthy acidity. Building your own rye starter is easier than you think, so if you have the time, try making your own. If you're in a hurry, stop by your local bakery and ask nicely. Most bakers are happy to share a bit of sample starter to jump-start a good customer's home baking project. This home recipe also includes a small percentage of dry instant yeast; this added leavening acts as insurance against irregularities in home starters.