How does sourdough bread get its flavor?

Sourdough flavor emerges from a layered interaction of microorganisms, grain chemistry, dough handling, and heat. Wild yeasts and lactic acid bacteria in a starter feed on flour components and produce organic acids, alcohols, esters and other metabolites that give sourdough its characteristic tang and aromatic depth. Marco Gobbetti at the University of Naples Federico II has described how the metabolic activity of these communities generates a broad palette of volatile and nonvolatile compounds that distinguish sourdough from breads made with commercial yeast.

Microbes shape taste and aroma
Lactic acid bacteria contribute acidity and complexity by producing lactic and acetic acids, which create the sourness and also modulate perception of sweetness and aroma. Heterofermentative bacteria produce acetate and other byproducts that add sharp, tangy notes; homofermentative strains produce mostly lactic acid and a milder profile. Wild yeasts generate carbon dioxide for leavening and release ethanol and aromatic molecules such as higher alcohols and esters, which are perceived as fruity or floral. Specific microbial pairings—such as the association of Lactobacillus sanfranciscensis with particular sourdough traditions—help explain regional flavor signatures. Michael Gänzle at the University of Manitoba has emphasized that local microbial ecology and fermentation conditions shape the balance of these compounds, so two starters grown from the same flour can evolve distinct flavor profiles over time.

Dough chemistry and baking effects
Enzymes inherent to flour and those released by microbes break down starches and proteins into sugars and amino acids that are precursors for flavor formation. During baking, the Maillard reaction between reducing sugars and amino acids produces dozens of aromatic compounds responsible for toasty, nutty, and caramelized notes; crust formation concentrates these flavors and generates different volatiles than the crumb. Acids produced in fermentation change dough pH, which alters enzyme activity and protein interactions, influencing texture as well as flavor release in the mouth.

Relevance, causes, and consequences
Flavor determines consumer preference, market value, and cultural identity for many communities that prize traditional sourdoughs. The causes of flavor differences—variations in starter microbiota, flour type, hydration, fermentation time and temperature—are also consequences for shelf life and food safety: acidified doughs tend to inhibit spoilage organisms and some pathogens, extending keeping quality. The choice of locally grown grains and ambient microbes ties sourdough to territory and culinary heritage, so preserving traditional techniques can support biodiversity of food cultures and provide small-scale bakers with distinctive products.

Understanding sourdough flavor therefore requires attention to microbial ecology, biochemical pathways and baking chemistry, plus the human practices that select for certain tastes. Research by authorities such as Marco Gobbetti at the University of Naples Federico II and Michael Gänzle at the University of Manitoba provides a scientific basis for why starter management, flour choice and fermentation conditions matter for the sensory character and safety of sourdough bread.