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.

Impact of Temperature

• 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.

Impacts of Salts and Fats

• 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.

Impact on Dough's Texture and Quality

• 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.

Dough Leavening

• 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.