In: Chemistry
Yeast are unicellular eukaryotic organisms that have been utilized for thousands of years to produce leavened (risen) bread and alcoholic beverages. To make leavened bread yeast are added to the bread dough and once it is placed in a warm place, the yeast cause the bread to rise. Knowing what you do about glycolysis and the fates of pyruvate, explain biochemically why the bread rises.
Yeast contains enzymes that are able to break down the starch in the flour into sugars; first using amylase to break down the starch to maltose, and then using maltase to break down maltose into glucose. This glucose acts as food for the yeast, and it metabolises it to produce carbon dioxide and ethanol.
In bread making, the yeast organisms expel carbon dioxide as they feed off of sugars. As the dough rises and proofs, carbon dioxide is formed; this is why the dough volume increases. The carbon dioxide expands and moves as the bread dough warms and bakes in the oven. The bread rises and sets.