Yeast Fermentation

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Submitted By beno2009
Words 1963
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Yeast Fermentation
Copyright © 2000 Sarah Phillips Sarah Phillips, Inc. All rights reserved.

Yeast is the most commonly used leavener in bread baking and the secret to great bread making lies in its fermentation, or the metabolic action of yeast. It is the magical process that allows a dense mass of dough to become a well-risen and flavorful loaf of bread. In order for fermentation to take place, all yeast needs food, moisture and a controlled warm environment. Its byproducts from consuming food are the gas carbon dioxide, alcohol, and other organic compounds. The gas is the rising agent in bread, and the other "waste" products create the subtle flavors and texture that make a good loaf.

HOW DOES IT WORK?
In bread baking, we are trying to ferment grain in order to leaven it. We are also trying to release sugars trapped in the complex starch molecules to be used as yeast food, and much of it for flavor and crust color (caramelization). Yeast is a single-celled organism and only certain strains are used for fermenting grain.

Yeast activation and the initiation of fermentation are triggered by hydration, from either water or some other liquid, and the presence of a food source. Fermentation ends at 140 degree F during baking when heat kills the yeast. (Fermentation can end earlier, if the yeast is killed by other factors.)

Yeast feeds on sugar derived from the complex starch molecules from flour, a complex carbohydrate. The starch molecules are broken apart into simpler sugar molecules from enzymes in the flour when hydrated. Flour tastes like sawdust because its sugar components are too complex to differentiate on the tongue. The enzyme is a catalyst, which breaks apart the threads, freeing them so they become accessible to yeast and bacteria. Yeast lacks amylase and cannot break down starch into sugar. Since flour's endowment of sugars can only feed…...

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