High temperatures strengthen the network that has formed between the proteins during kneading, and
the network becomes more and more rigid. Simultaneously, the starch in the starch granules
gelatinise, taking up water, and this effect, combined with the level of water evaporation causes the
dough to start to harden.
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Diagram showing the starch granules (grey) swelling, while the proteins form a network around the
bubbles of gas (white)
Temperatures at the breads surface increase faster than inside the bread. This forms a dry and hard
crust, which prevents any gases from escaping, maximising swelling of the dough. Therefore bread is
often cooked in a very hot oven to initiate the solidification of the crust, which reduces subsequent gas
escape and a decrease in bread volume. Dishes such as quiches are also cooked at a high
temperature to ensure this impermeable crust on the surface to prevent significant amounts of water
vapour from escaping. This is so that sufficient water vapour is still there at the end of cooking to
condense, and ensure that the quiche remains tender on cooling.
As the gases, which are unable to escape, continue to expand, the pressure inside the dough
increases. This increase in pressure causes some of the protein network to be broken, which allows
the gas bubbles to interconnect with each other.
As temperatures at the surface exceed 100 °C, Maillard reactions begin to occur between the reducing
sugars and the amines in the crust, producing the noticeable colour and taste of bread. In the
presence of milk, these Maillard reactions are even more favourable. Milk contains the sugar lactose,
which, unlike maltose, can not be broken down and used as a food source by the yeast, so its
inclusion in the original dough provides an increased total sugar concentration available for Maillard
reactions, improving the breads brown colour and the taste.
Cooking bread at too high a temperature may cause the protein network to become too rigid, due to