What Happen During Baking a Bread?

Baking is a critical process in bread processing the high energy reaction phase maximizing chemical and physical transformations of dough into finished products. Basically purpose of baking are drying, coloring and cooking. Princple of baking process can describe as below process.   Behind this simple description are a great many different physical and chemical changes, which are summarised as follows. Gas production by the yeast continues as the dough temperature rises in the early stages of baking. When all of the dough exceeds 43 ºC the rate of gas production falls and eventually ceases by 55 ºC. While the dough surface is rapidly heated and yeast activity ceases there the poor heat conductivity of dough means that the centre continues to produce carbon dioxide gas for some time after the crust has formed. The force that is created by the expanding centre means that tin dough springs upwards, creating oven spring. The dough is also being expanded by steam pressure and the expansion of trapped gases. The dough loses moisture with increasing baking time. The moisture losses are greatest from the crust and this encourages the formation of a crisp eating, crusty layer. The Millard reactions begin to develop the crust colour.   The starch begins to swell and gelatinise. At this time more of it becomes susceptible to the action of any -amylase enzymes present and the breakdown to sticky dextrin and maltose is accelerated by the higher temperatures. In the dough the gas bubbles present are separated from one another by a thin protective film. Since they are not connected with one another they are commonly described as‘foam’. As baking proceeds, the loss of water makes the gluten protective film become more rigid and the pressures within the gas bubbles rupture the protective films. The foam in the dough is converted to a sponge, which is a system in which all the cells are open and interconnected. At this time the volume of the baking loaf falls slightly as the internal and external gas pressures are equalised. Moisture continues to be lost while the product remains in the oven. All of the necessary changes from dough to baked product are usually achieved by the time that the product centre reaches a temperature between 92 and 96 ºC.