Sourdough, also known as naturally leavened bread, uses a natural bacterial culture as the leavening agent instead of commercially produced dry or fresh yeast. A sourdough culture or levain is a combination of flour and water that must be kept alive through routine feedings of more flour and water. The naturally existing yeast found on the grains of the flour (and to some extent in the air around us) become active when water is added to flour; the yeast excrete carbon gas as a byproduct of consumption, which leavens bread dough.
Sourdough bread is a labour-intensive process due to the extended proofing (rising) time required of the natural levain. Our bread undergoes a 24-hour fermentation process, as opposed to bread made with commercial yeast (which can take as little as three hours). It has been reported that the extended fermentation time helps break down enzymes that are suspected to cause some people digestive discomfort. It also produces a more varied, nuanced and flavourful loaf of bread.