Final answer:
Punching down dough after its first rise is done to release accumulated carbon dioxide, redistribute yeast and gluten, and create a better texture for the finished bread. It also helps in forming a skin to control the bread's expansion in the final rise.
Step-by-step explanation:
You punch down dough after it has risen to release the carbon dioxide gas that has built up during the first rise. Yeast in bread dough carries out alcoholic fermentation, consuming sugars and releasing carbon dioxide as a waste product. This release of gas forms bubbles that cause the dough to expand, creating the small holes you see in bread.
As the dough rises, it effectively doubles in size, similar to the analogy of a loaf of raisin bread where the raisins move farther apart as the bread expands. Punching down the dough collapses these gas pockets, redistributes the yeast cells, and gluten within the dough, and ultimately leads to an even crumb structure and better texture in the finished bread. Furthermore, the process of punching down the dough allows the bread to form a skin, controlling the direction in which it will expand during the final rise and baking.
Aside from the practical reasons, historically, artisanal breads relied on wild yeasts, and the unpredictability of these natural yeasts often led to the discarding of many batches of dough. Modern yeast strains have made bread production more consistent and less laborious.