Bread dough incorporating ingredients that contain fat or sugar is considered enriched dough. By adding eggs to yeast bread, you impart flavor, build structure, develop color and even add nutritional value. Examples of yeast bread containing eggs include the Jewish bread for Sabbath and holiday, challah, and the French pastry bread, brioche.
One of the golden rules of baking is that fat equals flavor. By incorporating eggs into yeast bread, you are adding the sweet, buttery flavored fat of the egg yolk, resulting in a richer overall taste. As there is relatively little flavor in egg whites, they do not play a significant role in the overall taste of bread, and some recipes call for one or two whole eggs plus several egg yolks.
The fat in egg yolks helps shorten the gluten strands in bread dough, increasing the gluten's elasticity. This results in a more tender crumb and softer crust in the finished bread. Additionally, the coagulating property of eggs, due to their protein, helps create a more tender and even texture. As a leavening agent, the eggs contribute to the bread dough rising higher than a non-egg yeast bread.
For an extra light loaf of bread, substitute 1/4 cup of the recipe's water with two egg whites whipped to peaks. Fold the whites into the bloomed yeast immediately before mixing in the flour. The air bubbles in the egg whites will expand during cooking to yield an extra light and tender crumb.
The lipids in egg yolks give color to the crust of yeast bread. Due to this heavier coloration than egg-less dough, baking temperatures should be reduced slightly to prevent too much coloration. The protein in the eggs also contributes to the Maillard reaction, the chemical change that causes browning of bread's crust, which relies on the presence of heat, moisture, protein and sugars.
Adding eggs to yeast breads enhances the nutritional value of the dough. Eggs are among the most nutrition-dense foods we eat, containing the essential fatty acid linoleic acid, calcium, iron, potassium, vitamins and even antioxidants. Though an entire loaf of bread may contain only a few eggs, the benefits still add up, making the enriched dough a way to sneak in extra nutrition to a carbohydrate-rich staple.