What is a common leavening agent used aside from steam in various pastries?

Baking soda is a commonly used leavening agent in various pastries because of its ability to produce carbon dioxide gas through a chemical reaction with acidic components present in the mixture. When baking soda is combined with an acid (such as buttermilk, yogurt, or vinegar), it generates bubbles of carbon dioxide, which helps to lighten the dough or batter and create a fluffy texture in baked goods. This reaction occurs quickly, making it ideal for recipes that require a quick rise, like cakes, muffins, and cookies.

The other options serve different purposes; for example, vinegar is often used in conjunction with baking soda as an acid to activate the leavening process, but it is not a leavening agent by itself. Yeast is a biological leavening agent that ferments sugars to produce carbon dioxide, but it typically requires longer rising times compared to the rapid action of baking soda. Salt is primarily used for flavor enhancement and does not contribute to leavening directly. Thus, baking soda stands out as the preferred choice for immediate leavening in various pastry recipes.