It's an interesting food-science factoid that beer and bread are twin siblings in the culinary world. Both rely on the interaction of grains and yeast, and a process called fermentation. In bread, fermentation has many positive effects on the final outcome. It is responsible for the flavor, texture and rise of the finished loaf.
What Is Fermentation?
Fermentation, simply stated, is a byproduct of the normal life cycle of yeasts, a family of microscopic fungi. Yeasts feed on a variety of sugars, either refined sweeteners or those that naturally occur in grain or other foods. The sugars are digested by the yeast and turned into carbon dioxide and alcohol, which provide the primary leavening for yeast doughs. The activity of the yeast is complemented by colonies of benign bacteria, which in turn break down the alcohol into a variety of compounds that add to the flavor of the dough.
When flour is mixed with water, the proteins in the flour begin to unwind and bind together, creating long strands called gluten. Gluten strands form naturally with the passage of time, but the process can be accelerated by stretching, which is what happens when we knead the dough. As the yeast turns sugar into carbon dioxide, the gas seeps into small air pockets in the dough and is trapped by the gluten in small bubbles, like tiny balloons. This is what makes the bread rise, and in the process the gluten is stretched and developed further.
The fermentation process also has a significant impact on the flavor of the finished loaf. When the yeast works too quickly, it produces excessive amounts of alcohol. This makes a bread with a coarse, dry texture and an unpleasant flavor. When the bread is given a slower, cooler rise, this creates an opportunity for the slower-growing bacteria to catch up with the yeast and begin converting alcohol into flavor compounds. Artisanal bakers deliberately slow or "retard" the fermentation of their loaves to allow time for this to happen.
Changes in Texture
When a dough is first mixed, it is stiff and often sticky to the touch. If the ball of dough is pulled in half, it will tear easily and leave a rough edge. After fermentation, the dough feels entirely different. It is light and soft, filled with air pockets that give it a fluffy texture. It is also flexible, and if you attempt to pull the dough in half it will stretch out into long, thin strings before parting. At this stage, the dough can be stretched and rounded to form balls or oblong shapes, which can be formed into loaves.
- "On Food and Cooking: The Science and Lore of the Kitchen"; Harold S. McGee; 2004
- "The Bread Baker's Apprentice: Mastering the Art of Extraordinary Bread"; Peter Reinhart; 2001
- Fine Cooking; Yeast's Crucial Roles in Breadbaking; Shirley Corriher
- Baking 911; How Yeast Fermentation Works; Sarah Phillips; 2008
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