Baking
Once our dough has been properly fermented, shaped, proved, and possibly slashed, it is time to bake it. Baking transforms dough into bread via a number of physical and chemical processes.
Oven Spring
In the first few minutes of baking, the dough rises dramatically. This "oven spring" or "oven kick" is caused by an increase in fermentation as the heat stimulates the yeast (until the dough is hot enough to kill the yeast at around 60°C/140°F), and the thermal expansion of the gas bubbles already in the dough. We can maximise oven spring by injecting steam into the oven before the loaves go in, and during the first few minutes of baking. The steam conducts heat into the dough much more quickly than dry air would, and it keeps the surface of the dough moist and elastic, so that it can stretch and allow the dough to expand.
All Steamed Up ...
Amateur bakers have shown great ingenuity in trying to replicate this steam injection in domestic ovens: the most common methods are to preheat a deep metal tray on a low shelf and pour in hot water when putting the loaves onto the top shelf, and to spray water into the oven using a plant misting spray several times during the first few minutes of baking. I have found that using a cheap electric steam cleaner (mine cost under 20 UK pounds) is much more effective and straightforward. For more details and suppliers, see the Other Equipment page.
From Dough to Crumb
As the dough heats up in the oven, water from the dough evaporates, making the finished loaf drier and lighter than the original dough - a loaf can lose up to 20% of its mass during baking. The heat also causes a reaction called gelatinization (or gelation) in which starch molecules in the dough absorbs water until they reach a temperature between 80 and 100 celsius, at which point they burst, releasing starch which thickens the water in the dough, which then solidifies into the slightly translucent crumb. The internal temperature of the bread when this takes place is between 82° and 100° Celsius (180° and 212° Fahrenheit) so many bakers use a digital probe thermometer to test when the bread is done. According to Peter Reinhart (see "The Bread Baker's Apprentice" in the further reading section), an internal temperature of at least 80°C (176°F) is needed for dinner rolls, 85-88°C (185-190°F) for full sized softer loaves for sandwich bread, and 93-99°C (200-210°F) for crusty bread.
At the same time, the walls of many of the bubbles in the dough will burst, changing the structure from a sponge (which would collapse as the bread cooled) to an open lattice where each cell is connected to its neighbours. This open lattice is responsible for the hollow sound that a properly cooked loaf will make when tapped on the bottom.
Crust Formation
As the gelatinization of the crumb is taking place, the crust is also forming. The combination of sugars, protein, and heat lead to a complex process called the Maillard reaction, which causes the crust to brown and releases many characteristic flavour compounds. Crust formation is further enhanced by caramelization as the temperature rises. Since the crust is on the outside, it loses more water through evaporation than the crumb. So, a loaf with a large surface area, such as a baguette, will have a higher ratio of crust:crumb than a rounder shape such as a boule. Note that it you are very unlikely to burn most types of bread, and the best flavour will be obtained from a dark, richly browned crust, so if in any doubt, give it a few more minutes in the oven.
Cool It!
Remember that baking is not the final stage of bread making: once you have checked that the bread is cooked (either with a digital probe thermometer or by tapping the bottom of the loaf) you must let it cool. Take it out of the oven and place it on a wire rack, which will allow water vapour to escape from under the loaf, avoiding a soggy bottom. Allow the bread to cool completely before cutting, otherwise much of the moisture will escape, making the remaining bread dry out. The full flavour of bread is not apparent until it is cooled - indeed many people find that sourdough bread does not develop its fullest flavour for another 24 hours.
Keeping it crunchy
When bread is fresh out of the oven, most of the remaining moisture is in the crumb, so the crust is relatively dry and crunchy. After a few hours, some of the moisture will have spread and been absorbed into the crust, making it somewhat soft. It is possible to get that crunch back by putting the loaf back into a hot oven for five minutes, but only do this once for each loaf, and preferably before it's been cut, otherwise the bread will dry out.
That concludes our overview of the baking process, so why not have a look at the recipes page and get baking?