What gases and flavour compounds does yeast fermentation produce in bread dough?

During the process of yeast fermentation in bread dough, the yeast cells—primarily Saccharomyces cerevisiae—metabolize fermentable sugars such as glucose, fructose, maltose, and sucrose. This biological activity produces two primary substances:1

• Carbon Dioxide: This gas acts as the essential leavening agent. As it is trapped within the dough, it creates an airy texture and causes the bread to rise.123
• Ethanol: This alcohol is a significant byproduct of fermentation and serves as a key component in the aroma of freshly baked bread. Although produced during fermentation, most of the ethanol is driven off during the baking process.13

In addition to these primary products, yeast activity generates various other compounds that contribute to the development of the bread's characteristic flavor and influence the physical properties of the dough. In the case of sourdough, the fermentation process also involves wild yeasts and bacteria, which can produce additional compounds responsible for the bread's distinct sour flavor.1245