What leavening agent is used in croissant dough?

Yeast is the leavening agent used in croissant dough. Croissants are made from a laminated yeast dough, which places them between bread and puff pastry: yeast provides fermentation, while butter-and-dough layers create flakiness.

During proofing, yeast consumes sugars and releases carbon dioxide. That gas becomes trapped in the dough’s gluten network, making the shaped croissants expand before baking. The dough is usually kept cool so the butter remains firm during lamination and the yeast develops at a controlled pace.

Steam also helps croissants rise, but it is not the dough’s biological leavening agent. In the oven, water in the dough and butter turns to steam, pushing apart the laminated layers and contributing to lift. Baking soda and baking powder are chemical leaveners and are not the standard agents in traditional croissant dough.

This yeast-based structure distinguishes croissants from ordinary puff pastry, which relies mainly on steam and does not contain yeast. It also helps explain why croissants need proofing before they go into the oven.