Saccharomyces converts starch or sugars to pyruvic acid through EM P pathway. Then this pyruvic acid is converted to acetaldehyde and finally to ethyl alcohol in the absence of oxygen. This entire process is called fermentation.C6H12O6-->2CH2COCOOH-->2C2H3OH+2CO2 This released carbon dioxide from yeast makes the dough to rise and gives spongy nature to bread.