Bread rises during baking in the oven thanks to the fermentation of sourdough or yeast. This fermentation produces carbon dioxide which creates air bubbles in the dough, giving the bread its volume and airy texture.
Yeast is primarily a small, living fungus. When it receives warm water and something to eat (flour, sugars), it comes into action. It consumes these sugars to live and mainly releases two elements: carbon dioxide and alcohol. The famous carbon dioxide is released in the form of small bubbles that get trapped in the dough. The longer the dough rests and rises, the more these bubbles increase in number. It is thanks to these small bubbles that the bread expands: they create space, the bread develops, gains volume, and becomes light and soft during baking.
Fermentation is the moment when the yeast starts to work seriously in your dough. It transforms the sugars present into carbon dioxide (CO₂) and alcohol, in the absence of oxygen. This CO₂ forms small bubbles trapped in the dough, which gradually swell, causing your bread to rise. The more pliable and elastic your dough is, thanks to the gluten, the better it retains these gas bubbles, resulting in a well-aerated crumb. While all this ferments at room temperature or in controlled rising, the dough also develops a lot of characteristic flavors and aromas that will give your bread its typical taste.
Putting the bread in the oven triggers the final expansion. Why? Because the intense heat boosts fermentation and activates a sudden acceleration of carbon dioxide release by the yeast. Beyond 50°C, the yeast dies, but the CO2 trapped in the dough continues to expand significantly due to the heat. This expanding effect is what we call "oven spring" or steam burst. An ideal temperature generally hovers around 220°C to 250°C, hot enough for this expansion to be quick without the crust hardening too quickly. It is precisely in this ideal range that you achieve that famous well-aerated, light, and fluffy bread. Conversely, an oven that is too cold will give you a dense and heavy crumb. Too hot? It carbonizes the crust before the crumb has had a chance to rise properly, resulting in a dense crumb for sure!
Humidity plays a very important role during the bread baking process. At the beginning of baking, a humid atmosphere allows the bread to remain soft for longer, preventing the rapid formation of a rigid and dry crust. As a result, the bread can fully rise before its crust sets definitively. Water also helps the hot steam transfer heat to the dough more effectively, promoting a more even rise and good interior volume development. And obviously, it is often thanks to this steam that your favorite baguette has that beautiful shiny appearance and a crispy crust. Without sufficient humidity, the bread would often come out dull, underdeveloped, and much less appetizing.
The beautiful golden crust of bread coming out of the oven is largely due to the Maillard reaction. In simple terms, it is a chemical reaction between proteins (or more precisely, amino acids) and certain sugars under the influence of high heat. At around 140 °C, these compounds combine and create hundreds of new molecules, bringing roasted flavors and that lovely golden color. At even higher temperatures, another reaction comes into play: the caramelization of sugars, further enhancing the color and the typically roasted taste. Together, these two reactions give bread its crispy texture and irresistible flavor that everyone loves.
Natural sourdough bread, made from natural starters rather than industrial yeast, often requires a longer fermentation period, resulting not only in a distinctive aroma but also in better digestibility.
The golden crust of bread primarily comes from the Maillard reaction, a complex reaction between sugars and proteins, mainly activated during high-temperature cooking.
The famous French baguette is governed by specific rules: it must contain only four ingredients according to tradition—flour, water, yeast, and salt—with no additives allowed under the regulations for the 'tradition' designation.
The famous 'alveolated crumb' of bread is directly the result of the formation of carbon dioxide by yeast during fermentation, thus creating the various bubbles and air pockets within the bread.
A fully baked loaf of bread will sound hollow when tapped lightly on the bottom. You can also measure its internal temperature with a cooking thermometer: ideally, it should be around 90 to 95 °C.
Yes, you can slightly speed up the rising process by placing your dough in a warm spot (around 25 to 30 °C) and away from drafts. However, be careful not to exceed a temperature higher than 45 °C, as this could kill the yeast and prevent the dough from rising properly.
Generally, bread dough requires at least 1 to 2 hours for the first fermentation. However, some recipes suggest long fermentations of 8 to 12 hours, or even longer, to achieve a more developed flavor and aairier crumb.
A flattened bread after baking can be due to several factors: inactive or expired yeast, poor kneading, insufficient fermentation time, dough that is too wet, or inadequate baking temperature. Make sure to check the freshness of your yeast and follow a tried-and-true recipe for optimal results.
Yes, there are alternative ways to leaven bread, such as using sourdough or other leavening agents like baking soda or baking powder. These methods also produce carbon dioxide, but through slightly different chemical or biological mechanisms.
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