The dough traps bubbles released by the yeast because of the gluten present in it. The gas is caught in the elastic bit of the bread called gluten. When the proteins inside the dough develop contact with water, gluten takes form by swelling and creating a fine matrix in the dough.
The amount starts to increase once the two ingredients are kneaded together. The elastic molecule makes the air bubbles get trapped in the dough. To make the dough rise better, most recipes ask to leave the bread to rise twice. Once after the yeast is mixed and kneaded with the dough. Then again after an hour, the dough is kneaded again and left to rise for another hour.
This helps the yeast eat sugar and burp more carbon dioxide in the dough to make it airier. The yeast keeps doing their hard work even after the dough is placed in containers and placed in the oven. And after the baking is done, you have a delicious, fluffy loaf of bread that is based on science but for sure tastes like magic! A weekly guide to the biggest developments in health, medicine and wellbeing delivered to your inbox. Thank you for subscribing! Your subscription is confirmed for news related to biggest developments in health, medicine and wellbeing.
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This causes it to rise. During baking the carbon dioxide expands and causes the bread to rise further. The alcohol produced during fermentation evaporates during the bread baking process. AQA video: Investigating how raising agents work. These gases tend to be forgotten but without them it would not be possible to bake bread of the quality we expect. Their role increases in importance as the bread reaches the end of the bake time when its structure becomes more susceptible to collapse.
There are many ways of making bread from the basic ingredients of flour, water, yeast and salt, from labour-intensive artisan bread to high-throughput sandwich bread.
However, there are three aspects that are critically important to any type of bread making, and it all starts in the mixer:. The role of gases in expanding the bubbles during proving and baking is fascinating but usually focuses on yeast converting sugars to carbon dioxide CO 2. Yeast metabolism in dough is complex and involves a short aerobic fermentation stage where oxygen from the bubbles is used up followed by a much lengthier anaerobic stage.
The details of this are explained later. The mechanisms help to explain why the dough volume initially shrinks, why there is a lag before the dough gradually increases in volume and how oven spring takes place. However, as mentioned there are other leavening gases that play a vital role, particularly during baking, and without them the bread is certain to collapse in the oven.
This article highlights the role of the other gases together with the mechanisms by which those gases work to inflate the bubbles. Among the many research papers on bread dough leavening there a couple that are worthy of mention. These introduced the concept that gases other than carbon dioxide played a key role in expanding gas bubbles in dough. Moore and Hoseney calculated the carbon dioxide volume from expansion of the gas bubbles and concluded that carbon dioxide alone did not explain the increase in volume from dough to bread during baking.
A further publication on this subject was by Bloksma who compared the Moore and Hoseney calculations with his own on partial pressures of gases during baking. Bloksma included carbon dioxide, ethanol and water in his own calculations of thermal expansion. He concluded that water in the form of steam contributed more than half of the oven spring volume, with ethanol and carbon dioxide responsible for much of the rest. As mentioned previously, during bread baking there are several gases that contribute to the leavening of bread dough.
Carbon dioxide is the main gas associated with yeast leavened bread, however, other gases that play a role are ethanol, nitrogen and steam. There is also a small contribution from low molecular weight volatile compounds formed during fermentation.
The main gases and their roles are described in Table 1. Carbon dioxide generation takes place during two stages of fermentation because yeast can metabolise both aerobically and anaerobically.
Aerobic fermentation is the first pathway and will continue until all the oxygen is used up and the conditions in the dough become anaerobic.
There is competition with ascorbic acid for oxygen, added to increase gluten oxidation during mixing, and this limits the extent of aerobic fermentation. The yeast first metabolises glucose and oxygen to carbon dioxide and water, as in Equation 1. Glucose is generated by enzymic pathways from the starch in the flour to maltose and then to glucose.
Oxygen comes from the air in the bubbles entrained during mixing. Having used the available oxygen, subsequent fermentation during proof takes place with the dough in an anaerobic condition. Yeast obtains the oxygen needed directly from the glucose, according to Equation 2. This is by far the most dominant stage in yeast fermentation. Equal molar quantities of carbon dioxide and ethanol are produced from glucose breakdown, which are significant, and discussed later.
It is important to note that the carbon dioxide produced from either fermentation mode does not go straight into the gas bubbles.
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