The baking process transforms an unpalatable dough into a light, readily digestible, porous flavourful product.
- As the intense oven heat penetrates the dough the gases inside the dough expand, rapidly increasing the size of the dough. This is called "ovenspring" and is caused by a series of reactions: Gas + heat = increased volume or increased pressure. Gas pressure inside the thousands of tiny gas cells increases with the heat and the cells become bigger.
- A considerable proportion of the carbon dioxide produced by the yeast is present in solution in the dough. As the dough temperature rises to about 40°C, carbon dioxide held in solution turns into a gas, and moves into existing gas cells. This expands these cells and overall the solubility of the gases is reduced.
- The oven heat changes liquids into gases by the process of evaporation and thus the alcohol produced evaporates.
- Heat also has an effect on the rate of yeast activity. As the temperature rises the rate of fermentation increases, and so does the production of gas cells, until the dough reaches the temperature at which yeast dies (approximately 46°C).
From about 60°C onwards stabilisation of the crumb begins. Starch granules swell at about 60°C, and in the presence of water released from the gluten, the outer wall of the starch granule cell bursts and the starch inside forms a thick gel-like paste, that helps form the structure of the dough.
From 74°C upwards the gluten strands surrounding the individual gas cells are transformed into the semi-rigid structure commonly associated with bread crumb strength.
The natural enzymes present in the dough die at different temperatures during baking. One important enzyme, alpha-amylase, the enzyme which breaks starch into sugars, keeps on performing its job until the dough reaches about 75°C.
During baking the yeast dies at 46°C, and so does not use the extra sugars produced between 46-75°C for food. These sugars are then available to sweeten the breadcrumb and produce the attractive brown crust colour.
As baking continues, the internal loaf temperature increases to reach approximately 98°C. The loaf is not completely baked until this internal temperature is reached. Weight is lost by evaporation of moisture and alcohol from the crust and interior of the loaf. Steam is produced because the loaf surface reaches 100°C+. As the moisture is driven off, the crust heats up and eventually reaches the same temperature as the oven.
Sugars and other products, some formed by breakdown of some of the proteins present, blend to form the attractive colour of the crust. These are known as "browning" reactions, and occur at a very fast rate above 160°C. They are the principal causes of the crust colour formation.