Understanding yeast fermentation and effects on dough

Yeast Fermentation Basics

Yeast is a type of fungi that plays a crucial role in bread baking. It ferments sugar, resulting in carbon dioxide and ethanol. This process is called yeast fermentation.
The carbon dioxide produced during fermentation causes the dough to rise and create the space, or ‘holes’, seen in the bread’s crumb.
The ethanol evaporates during baking, contributing to the flavour and aroma of the baked goods.
Yeast is usually activated in lukewarm water with sugar, a stage known as proofing. This process kickstarts fermentation.

The rate of yeast fermentation is greatly influenced by temperature. Yeast is most active between 27°C and 32°C. Temperatures above 50°C can kill yeast.
In dough refrigeration, a process called retardation, fermentation slows but still occurs. This enhances flavour and texture.

Salt positively affects dough by strengthening gluten structure, slowing fermentation, and enhancing flavour.
Fats slow down yeast fermentation by coating the gluten proteins, which affect the formation of the dough’s structure.

The carbon dioxide gas expansion during the baking process helps in opening the dough’s structure and provides a desirable light, fluffy texture.
The by-products of yeast fermentation react with other dough ingredients during baking, leading to complex flavours and pleasing aromas.
Over-risen dough can cause yeast to exhaust its food supply, resulting in dense textures and less appealing flavours. Therefore, controlling fermentation is key in producing quality baked goods.

Yeast fermentation is one main type of leavening in baking. Others include chemical leavening (baking powder/soda), steam (in pastries, e.g. puff pastry), mechanical (air incorporation e.g. whisking), and biological (sourdough leavening).
Yeasted dough products include bread, yeast-raised pastries, and some types of rolled-in dough.