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Bread proofing, or proving, is the final step in making leavened bread before the actual baking and during which shaped dough is allowed to rise one final time. After mixing ingredients and allowing the dough to rise, the baker will punch, knead and shape the dough before letting it rest during bread proofing. Some recipes, however, refer to any time the dough is allowed to rise, including the initial rise, as bread proofing.
Fermentation is responsible for causing bread to rise. When yeast is mixed with the flour and water, it begins to convert carbohydrates into simple sugars that it can use. As the yeast feeds on these sugars, it produces alcohol and carbon dioxide. Warm temperatures speed this process along, but temperatures of more than 140 degrees Fahrenheit (60 degrees Celsius) kill the yeast and stop the reaction.
Mixing the flour and water also makes gluten, the substance responsible for giving dough its strength and elasticity. This elasticity causes the dough to trap the carbon dioxide in tiny air bubbles. As more of these bubbles become trapped, the dough takes up more space and begins to inflate, or rise. Gluten stretches around these tiny bubbles, making an intricate mesh laced with tiny hollows. After the bread is baked, these hollows created by the bubbles give the bread its light texture.
For the first rise, the yeast becomes active as it mixes with flour and water. This mix initially is uneven, and during the mixing and kneading process, some of the yeast is completely dry, and some is fully activated and producing carbon dioxide. As a result, the first rise might not grow evenly. Portions of the dough might be too dense, and other portions might overproof and spring leaks in the dough’s surface. Bread proofing evens out the leavening process for a more consistent loaf.
After the first rise, the baker will punch down the dough and squeeze out most of the carbon dioxide. With all yeast in the dough now fully active, the dough will rise evenly. Even, predictable rising allows the baker to shape the loaf as desired without the risk of one side inflating more than another. Stretching the dough tight and tucking it underneath itself also will help trap carbon dioxide more completely for a lighter bread.
The length of time required for bread proofing will depend on the recipe that is being used. Dough made with rye flour, for instance, rises especially quickly. On the other hand, sourdough bread might need to ferment for days. Of course, the desired density also will have an impact on the proofing time as well, and recipes using similar ingredients might call for different treatments.