One of the many possible sides to many meals is bread. Whether it is in a roll, a loaf, a sweet bread, or a bowl, it is known to compliment most dishes, and the fresher it is the better. For some the smell of fresh baked bread is both nostalgic and invigorating. The types of bread that are available to bake typically fall into two categories leavened and unleavened.(1)
Today we will be going over the leavening process that is seen in many types of bread and how it relates to chemistry. The common leavening agents that are used are baking soda/powder and yeast. Ingredients that comprise most forms of bread are broken down into water, flour, salt, yeast, and for bread that rises a sugar source and fat source.(2,3) The optimum ratios for yeast, flour, and sugar to make bread rise is half cup of sugar to 4 cups of flour with 2 and a quarter teaspoon of yeast.(3 )Also it is suggested that there is a 1% yeast to flour ratio (i.e., 3 g of yeast for 300g flour.)(3)
The process by which the yeast aids in the rising of the bread dough is fermentation. The yeast will break down the sugar source in the recipe(glucose) into carbon dioxide (CO2) and ethanol (CH3CH2OH). For every sugar molecule that is broken down by the yeast, 2 molecules of carbon dioxide and 2 molecules of ethanol are converted. When the bread dough is kneaded in the mixing process, the gluten which is present in the flour source forms branched chain structures that would capture the carbon dioxide gas that is released during the fermentation process and use it to help the bread rise in its container. The ethanol is typically cooked off in the process of baking but adds flavor and color to the bread. The amount of sugar also controls moisture content, crumb structure, and color of the crust.(4)
Review of the fermentation process in baking bread:
· Common leavening agents are baking soda/powder and yeast
· 4 main ingredients in bread are: water, salt, flour, yeast
· Fermentation breaks down glucose into carbon dioxide and water
· Sugar content controls breads rising rate, moisture content, crumb structure and crust coloring
· Suggested yeast to flour ratio is 1% yeast to flour.
View the activity below to show the balanced chemical reaction for the fermentation process.
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