Do not confuse sourdough with natural yeast. Sourdough is a bacteria culture. Natural yeast is just that, a yeast culture. To make a yeast culture keep your starter in the refrigerator, as I have for the last 20 years. For a sourdough starter keep your starter on the counter. Sourdough has some health benefits, but natural yeast can actually cure celiac and leaky gut. Also, many allergies can be reduced or even cured by using natural yeast. JUNIPER berries are the source of the most healthy, gut-healing yeasts. Wild gathered berries are best, but if not, look for a white dust on the berries. That is the yeast. Happy baking!