The leavening for puff pastry and items baked with pate a choux are the same. What leavens the pastries?

• A. Air
• B. Steam
• C. Baking Powder
• D. Yeast

Answer: (B)

Steam is the lifting force in both puff pastry and choux pastries. As the pastries bake, the moisture in the dough turns into vapor. That steam pushes against the surrounding dough and fat layers, inflating the pastry and creating the characteristic puff or hollow interior. In puff pastry, the many thin fat layers trap steam to separate and lift the sheets, giving flaky, light layers. In choux, the dough is deliberately high in moisture and cooked enough to set the starch and eggs; when it hits the oven, the rapid steam expansion inflates the dough into a hollow shell that dries into a crisp structure. Air plays only a minor, incidental role, and traditional puff and choux rely on steam rather than chemical leaveners like baking powder or yeast.