When you put bread into a toaster and it becomes toast, the bread undergoes a chemical and physical transformation. The transformation occurs due to the heat applied during the toasting process. Here's what happens:
Evaporation of Water: Bread contains a significant amount of water, and when you put it into the toaster, the heat causes the water within the bread to evaporate as steam. This process removes moisture from the bread.
Caramelization: As the bread heats up, the natural sugars present in the bread begin to caramelize. This is a chemical reaction that occurs when sugars are exposed to heat, resulting in the browning or golden color on the surface of the bread.
Maillard Reaction: Along with caramelization, the Maillard reaction also takes place. This reaction occurs between amino acids (proteins) and reducing sugars in the bread when subjected to high heat. It contributes to the development of flavors and the characteristic aroma of toasted bread.
Formation of Toast: The combination of water evaporation, caramelization, and the Maillard reaction results in the transformation of the bread into toast. The toast is drier, firmer, and has a different flavor profile compared to the original bread.
So, the bread does not disappear; rather, its physical and chemical properties change during the toasting process, turning it into what we know as toast.