After you have allowed your loaves to fully proof you will need to transfer them to your oven quickly and carefully. You don’t want the oven to lose too much heat, but you also don’t want to damage your loaves while you put them into the oven. The easiest thing to do is to line your baker’s peel with parchment paper and then place your loaves on the parchment. This way you won’t have to worry about your dough sticking to your peel. As soon as your bread is on the stone throw a half a cup of water into the cast iron skillet and quickly close the door. Don’t be tempted to open the door at this point. You should wait until the bread has baked at least half the amount of time it is supposed to before you open the oven door.
Now is the time when the oven spring happens. It occurs, because the gluten-strengthened cells you created during kneading quickly inflate with gases. The other processes that are happening are that the alcohol in your dough (which was created by the yeast) begins to boil, the yeasts become more active because of the intense heat, and steam is produced from the water in the dough. Your bread dramatically increases in size during these initial minutes, but it reaches its max size about fifteen to twenty minutes into baking.
There are a lot of different things going on in your bread during baking. As the interior of the bread heats up the starches gelatinize. When the dough hits about 140 degrees then the chains of starches undergo molecular changes that cause them to uncoil and absorb water. It is at this same temperature that the proteins coagulate, releasing the water that was trapped within. The swollen starches and cooked gluten strands become firm and trap the gases within the air cells. The crust of your bread is drying out and is firming up more quickly than the inside. Around 325 degrees, the sugars in the crust begin to caramelize, which results in browning. The rest of the browning is caused by the Maillard reaction, which is a chemical reaction between amino acids and simple sugars in the crust. This reaction is responsible for the wonderful smell of baked bread.
The interior of the bread takes much longer to cook than the crust does. When the heat of the oven begins to reach the interior of the dough, the water in the dough migrates toward the crust. This is called starch retrogradation or basically the redistribution of water molecules. When the interior reaches 200-205 degrees, then the dough begins to firm up. This does not necessarily mean that your bread is done. It may be the right temperature, but the crust may not be fully baked. Follow your recipe and its description for what the crust should look like, the internal temperature it should be, as well as the sound it makes when tapped lightly on the bottom. The crust should also be firm and resist being squished.