I started my own sourdough starter about 10 years ago using the instructions in the King Arthur Flour Baking Companion cookbook. It took about a week for the starter to develop---it used flour, water, a little pumpernickel/rye flour and a teaspoon of molasses----no yeast---the concept is to provide the medium for the natural yeast in the air in your kitchen to develop and grow. I have been using this same starter ever since. Store it in the refrigerator when not baking---just take it out and feed it every 2 weeks if you aren't baking that often. I have read that different regions have different natural yeasts and that is why sourdough flavors can vary so much, besides the age of your starter. Try it, it makes the best crusty bread!!!