What is yeast?

• Yeast is a fungus composed of a single cell that is .006 to .008 mm wide. This microorganism has been used in making bread for more than 5,000 years, according to ExploreYeast.com, though bakers had no idea, until recently, how yeast impacted the bread-making process.

How it Works

• The strain of yeast used in making bread is called saccharomyces cerevisiae. It operates by consuming any sugar it comes in contact with, including sugars from wheat products, and in exchange it releases carbon dioxide and ethyl alcohol.

  Yeast operates most effectively under warm conditions, and the presence of salt helps to keep its activity in check.

Role in Bread

• Perhaps the most important role yeast plays in bread making is to help bread dough rise. As the yeast consumes sugar and releases carbon dioxide and alcohol, those byproducts meet the dough's air bubbles. There, the gasses begin to inflate and are trapped by the dough. As a result, the dough begins to expand, or rise.

  Yeast also contributes to the flavor and aroma of the bread. The fermentation process of yeast creates molecules such as organic acids and amino acids. These molecules are smaller and more flavorful than the molecules the dough began with. Bacteria in the dough also contributes to the bread's flavor, but yeast can interfere with bacteria's ability to survive by consuming all of the sugars in the dough. The more slowly the yeast works and the longer the dough takes to rise, the longer the bacteria can work to create flavors in the bread, too.

Other Uses

• Yeast and its fermentation is key in other products, too, especially alcoholic beverages. In beer and whiskey, for example, the yeast consumes the sugar of the grains used to make these beverages and releases carbon dioxide and alcohol. In making wine, the yeast consumes the sugar of the grapes, and the carbon dioxide by-product is allowed to escape form the liquid.

Yeast Gone Bad

• Making bread with yeast can be a delicate procedure. If the baker adds too much yeast, the loaf can fall flat or have empty pockets of air, or, if he adds too little yeast, the loaf can turn out thick and chewy.

  In addition, temperatures must be carefully controlled when adding yeast to a recipe. If the yeast is too cold, it won't be activated and will be unable to work inside the dough. On the other hand, if the temperature is too hot, it will kill the yeast.