Why does freshly baked yeast bread have a distinctive aroma?

The distinctive aroma of freshly baked yeast bread is primarily the result of complex chemical processes occurring during fermentation and heating.

During the dough preparation stage, bakers’ yeast (Saccharomyces cerevisiae) ferments sugars, producing carbon dioxide and ethanol. While the ethanol is largely driven off during the baking process, it serves as a key component of the bread's characteristic scent.12

Additionally, the aroma is significantly enhanced by the Maillard reaction. This is a nonenzymatic chemical reaction between sugars and proteins (or amino acids) that occurs when the bread is heated. This reaction is responsible for the browning of the crust and the development of complex, savory flavor and aroma compounds that define freshly baked bread. Other products resulting from yeast activity also contribute to the overall flavor profile of the finished product.341