What is the primary leavening agent in puff pastry?

The primary leavening agent in puff pastry is steam. Puff pastry is made using a lamination technique that involves layering dough with butter and repeatedly folding it to create thin layers. When the pastry is baked, the moisture inside the dough turns into steam, which expands and causes the layers to separate and rise. This results in the characteristic flaky, airy texture of puff pastry.

While yeast and carbon dioxide are common leavening agents in many baked goods, they do not play a significant role in puff pastry. Yeast relies on fermentation and requires time to rise, while carbon dioxide is a byproduct of yeast activity or chemical leavening agents. In puff pastry, the immediate and effective leavening action comes from the steam generated during baking, making it the correct answer. Air does play a minor role as it is incorporated during the mixing and handling of the dough, but it is not the primary leavening force.