How Does Yeast Work?

November 20, 2008

I like baking breads, so I found McGee’s paragraph about yeast’s chemical reaction interesting.

Yeast is a single-celled fungus, and comes in many species.  The one used for baking and brewing is usually Saccharomyces cerevisiae.  When baking a loaf of bread, enzymes in the flour break down the starch of the flour into the sugars glucose, fructose, and maltose.  The yeast then grows on these sugars, converting them into alcholol and carbon dioxide.

C₆H₁₂O₆ –> 2C₂H₅OH + 2CO₂

The above equation means one glucose molecule turns into two alcohol and two carbon dioxide molecules.  When the yeast causes this reaction in bread, the carbon dioxide inflates the dough and is trapped inside.  When cooked, however, both the carbon dioxide and the alcohol escape.  If your bread tastes alcohol-y or beer-y, it’s because not all the alcohol escaped during baking (I think).

Consider the effect in beer, the alcohol obviously remains, as does some of the carbon dioxide.

Posted in Food Science |