Why Does Yeast Raise Bread?

Yeast gives bread its enticing aroma and helps it rise correctly.

Yeast, a tiny, one-celled plant in the fungus family, needs air, starch and water to grow. It engages in a fermentation process that causes bread to rise, and it helps give bread both its soft structure and its incredible aroma.

Yeast

Although the baking process kills yeast cells, yeast is a live fungus that activates when mixed with warm water. Yeast feeds on the sugar and on starches in flour when it is introduced to the bread mix. It breaks the starches down into simple sugars.

Fermentation

As a byproduct of digesting sugars, yeast releases alcohol and carbon dioxide. The alcohol is destroyed in the cooking process, but carbon dioxide is left behind. Bubbles of carbon dioxide become trapped in the dough and the bread begins to rise. Keeping the dough warm as it rises encourages yeast to continue producing carbon dioxide.

Rising Bread Dough

Gluten, a natural wheat protein, stretches from all the carbon dioxide bubbles and the bread gains structure. By the time the dough rises to double its size, it is filled with carbon dioxide gas.

References

• University of Florida: Yeast-Questions and Answers
• Fine Cooking: Yeast's Crucial Roles in Breadbaking
• Michigan State University: How Does Yeast Work?