What You Need to Know
During kneading, gluten proteins (gliadin and glutenin) form a viscoelastic network that traps air. Butter is incorporated in discrete layers; when heated, the fat melts and steam expands, separating the layers. Yeast fermentation produces CO₂ and ethanol, which contribute to leavening and flavor.
The Science
Primary Reaction
Yeast fermentation producing CO₂ and ethanol, combined with gluten network formation and butter melting to create steam expansion