The oldest method to rise a bread is using sourdough. As soon as water is mixed with flour, yeasts and lacto bacteria which can be found in the flour starts to proliferate. Soon the first bubbles can be observed which is a sign of the microorganism activity. The microfauna starts to stabilize. In Spelt and Wheat sourdough the dominating species are the same, while in rye sourdough other bacteria species are predominant. The is the reason why rye sourdough is more sour than a wheat or spelt sourdough.