Pastry rises in the oven primarily because of gases expanding within the dough, mainly carbon dioxide produced by yeast or chemical leavening agents, as well as steam and air bubbles. These gases expand when heated, causing the dough to swell and rise. At the same time, the dough's gluten structure stretches to hold the gas bubbles, and the heat sets the dough's structure to maintain its risen shape.

Key Factors Making Pastry Rise

• Gases like carbon dioxide, steam, and air : Carbon dioxide is produced by yeast or baking powder/soda. Steam results from water in the dough evaporating due to heat. Air bubbles incorporated during mixing also contribute.

• Gluten structure : Flour proteins form gluten when mixed with water, providing elasticity and strength to trap expanding gases.

• Heat application : Oven heat causes gas expansion and water vaporization, inflating bubbles inside the pastry and causing it to rise.

• Setting of structure : As baking progresses, the heat dries and cooks the pastry, solidifying the gluten and starch network so it can hold the risen form.

This combination of gas expansion and setting of the dough is what creates the rise in pastries and baked goods during baking.