Sourdough Starter Guide
A Beginner’s Guide to Understanding Wild Yeast and Bacteria
What is a sourdough starter ?
In its most basic form, bread is made from four simple ingredients: flour, water, salt, and a leavening agent. Leavening agents release gas, expanding dough and creating openings in what would otherwise be a dense mass of flour and water. In the case of sourdough bread, a sourdough starter or mother plays this role.
A sourdough starter is a mixture of flour and water that acts as a substrate for propagating a diverse community of yeast and bacteria. These microbes originate from the environment and the grain used to create and feed the starter. When they encounter the nourishing and hospitable environment of fresh flour and water, they colonize the solution and begin to propagate. Over time and through successive feeding, the microbial community becomes a robust and lively culture that can be harnessed to leaven bread.
Yeast and bacteria each play a unique role in sourdough fermentation. Yeast provides most of the leavening power by producing carbon dioxide gas, which gets trapped in the dough, effectively causing it to rise. Bacteria, on the other hand, produce organic acids, including lactic acid and acetic acid. Acidification of the dough impacts the flavor and texture of the final product. It also allows sourdough bread to be stored for a longer period.
What makes sourdough different ?
Most store-bought bread is leavened with commercial yeast, available in fresh, dry active, or instant yeast. These are concentrated, single-strain cultures of Saccharomyces cerevisiae, a yeast selected for its ability to produce carbon dioxide rapidly and consistently. However, bread made with commercial yeast lacks notable bacterial activity. The result is bread that rises quickly and is baked soon after mixing – efficient yet lacking in flavor and digestible nutrients.
On the other hand, sourdough bread relies on the activity of a diverse community of wild yeast and lactic acid bacteria, which exist in a complex and dynamic ecosystem. The fermentation process is much slower due to lower levels of yeast activity. This gives the bacteria time to break down large molecules, like proteins, into smaller compounds, which are easier to digest and result in richer and more complex flavor profiles.
