Step 1 : Introduction to the question "What is the first stage of baking in the oven?"
...Baked goods go through several stages when they react to heat. But before anything else, they expand. Once in the oven, most baked goods start to grow almost immediately. A lot of that has to do with the gases in the batter or dough expanding. For example, really fluffy cupcakes are an indication of carbon dioxide in action.