What You Need to Know
Saccharomyces cerevisiae metabolizes fermentable sugars to carbon dioxide and ethanol, while co‑present Lactobacillus spp. convert sugars to lactic and acetic acids, lowering dough pH to 4.0–4.5. The acidification promotes enzymatic activity and suppresses spoilage microbes, and secondary metabolites such as acetaldehyde, diacetyl and various esters create the characteristic sourdough aroma.
The Science
Primary Reaction
Yeast: C₆H₁₂O₆ → 2 CO₂ + 2 C₂H₅OH; Bacteria: C₆H₁₂O₆ → lactic acid + acetic acid (and minor metabolites)