Bulk fermentation is the stage where the sourdough dough rises and develops flavor over several hours.

After mixing the starter (which contains the wild yeasts and bacteria) with flour and water, the dough goes through bulk fermentation. This means the dough is left to rest as one big mass, allowing the microbes to work their magic. The yeasts produce gases that puff up the dough, while the bacteria create acids that deepen the flavor. This phase can take several hours, depending on temperature and other factors. During this time, bakers often stretch and fold the dough to strengthen it and help develop the texture.