Sourdough is a cereal-based starter culture containing a colony of microorganisms including yeast and lactobacilli (lactic acid bacteria). Most rye-based sourdough starters are used in baking; they can, however, also be used for brewing beer.  The fermentation process begins when milled grain and water are added to a starter, or mother culture, and left to rest at a constant temperature. When flour comes into contact with water, the naturally occurring enzyme amylase breaks down the starch into sugars, which the natural yeast contained in the sourdough can metabolise, forming lactic acid and Carbon dioxide (CO2), thus leavening the dough.

Through the fermentation process the micro-organisms contained in the sourdough multiply, breaking down the components of the grain, such as Phytic Acid, which are more difficult to digest. Phytic acid is a known as a food inhibitor which prevents the bioavailability of the grain from being absorbed into the body. By allowing a sourdough sufficient time to rest, the enzymes break down the Phytic acid and the minerals contained within the grain, including Iron, Calcium, Magnesium and Zink, can be more easily absorbed.