Biochemistry in Bread Baking

In preparation of bread dough, a combination of yeast, water, flour, salt, and possibly other ingredients is made. The mixture is then kneaded to cause the flour proteins (gluten) to form a network that will give the dough its elasticity and enable it to hold the carbon dioxide produced by the yeast. The amylolytic enzymes, present in the wheat flour hydrolyze starch to maltose, providing a substrate suitable for yeast fermentation.

Fermentation begins, and the yeast at first uses the hexose sugars present in the flour and later utilizes some of the maltose released by hydrolysis of starch. Yeast undergoes alcoholic fermentation, producing ethanol and carbon dioxide gas, which aerates the dough.

C₆H₁₂O₆ 2C₂H₅OH + 2CO₂

The carbon dioxide bubbles are trapped in the gluten network and produce a large number of pores that make the bread rise.

Immediately before baking, the alcohol content of the bread is as high as 0.5%. The expansion of dough is attributed not only to the carbon dioxide released during fermentation, but also to the vaporisation of ethanol, with a small amount contributed by water vaporisation during oven baking. This process is known as the leavening effect.

The vaporised alcohol also helps to give the bread a pleasant aroma.

Bread Baking Processes

Bread Index