I usually make my own bread at home. When I bake bread in the oven, the smell is really attractive. It seems that I know why it emits fragrance?
In fact, bread in the process of baking, the surface will become brown yellow, emitting a good smell. This is due to a series of chemical reactions during baking, the most important of which is Maillard reaction. This reaction is very complicated and has not been fully understood up to now. In short, Maillard reaction is the reaction of sugar with amino acids at high temperature. This reaction releases some flavor compounds and polymerizes to produce dark colored substances. This reaction is also the main source of the unique aroma emitted during the roasting process.
If it is baked too long, the bread will be scorched and turn black. At this time, the bread was caramelized. Under continuous high temperature, starch molecules in flour will be broken into small molecules of sugar. These sugars will undergo molecular structure transformation, forming some volatile substances, some of which will also bring the flavor of baking. Some molecules will polymerize to form caramel pigments. As a synthetic pigment, caramel pigment is widely used in modern food. The black color of coke is produced by caramel pigment.
If the baking temperature is too high, the bread will be carbonized. The main component of flour is starch, accounting for more than 80%. Both starch and protein are organic substances containing a large amount of carbon. When heated without water, the organics will crack even if the temperature is not high enough to burn. Hydrogen, oxygen and other elements gradually lost, leaving only carbon and mineral components. The carbon left behind is black. Of course, such dark bread is not edible.