Fermenting your dough or letting it rise the first time is critical to having a light and airy loaf of bread. If you were to knead you dough and then immediately shape it and bake it would turn out like a hockey puck, very dense with little to no oven spring. During fermentation, yeast and bacteria within the dough feed off the sugars in the flour, producing carbon dioxide, alcohol, and acids. These by-products not only cause the dough to rise, but they also develop the distinctive flavors within the bread. Carbon dioxide molecules become trapped in the gluten webbing that you have developed during kneading, which cause the pockets in the dough to expand and raise the dough. You can not only see this process occur, but you can also smell a bit of an alcohol smell to your dough. You dough will rise best at a room temperature of 70-75 degrees. You will have to adjust the length of time you dough rises if your kitchen is much colder or warmer than this range. I always start to check my dough at the low amount of time given in the recipe, so if the recipe says that the dough should take between 1-1/2 hours to rise I start checking at the hour mark. This way your dough won’t over rise and become too gaseous. The more you make a certain type of bread the better you will become at judging whether or not it has risen enough. Most beginner bakers tend to under fermenting their dough versus over fermenting. A under fermented loaf will be denser because it did not rise enough, but over fermented dough is worse because the dough will also not rise well in the oven, but will also taste off. This is because the yeast have used up all or most of their food supply and they become weak. Most recipes will tell you what to look for when your dough has fermented to the proper size, because not all dough will double in bulk, some will go more, while others will only raise to one and a half times their original size.