The process by which yeast metabolises (consumes) simple sugars to produce carbon dioxide and alcohol (ethyl alcohol). The sugars come basically from three sources: a small amount of simple sugars naturally present in the flour, sugars that are converted from complex sugars to simple sugars through a series of conversion operations, and sugar that is released by enzymatic action on damaged starch in the flour (starch that is primarily damaged during milling). The carbon dioxide resulting from fermentation is trapped within the gluten structure, causing the dough to rise. The alcohol is converted to compounds that provide flavour and aroma to the finished crust.