I've read a lot of posts about not over-kneading the dough, partially because of over-oxidation of the dough that lowers the quality of it. But what exactly does oxidation do and why/how does it do it?
...There are several factors actually.Air: Oxidation on dough is caused by moving air, for the most part this is always bad for dough.Hydration: You are shooting for a perfect balance of Flour, Water and Yeast, all the way to the end of about 10 minutes in the oven, from the very first pre-ferment.
As you work the dough there are methods you can use to protect it from the surrounding air and also from actions that are robbing it of "wetness".If you pre-ferment for example overnight with a loose cover over the dough it will have a very gooie consistency.Now turn it out onto an open surface and let it rest for one hour un-covered...You will find a skin forming on your once beautiful dough. Very bad. ;-)
A certain amount of oxidation is actually a good thing for dough development. When gluten molecules are oxidized, sulfhydryl groups on certain amino acids are oxidized to produce disulfide bonds which contribute to the crosslinking of the gluten molecules. This is what helps form the gluten matrix. If the dough is over-oxidized, it starts to become problematic because now some of the compounds that contribute to the color, flavor and aroma of the bread are destroyed and the quality of the bread is diminished.