It is responsible for making bread rise and producing alcohol in beer and wine. Yeast is said to have first been noticed when an Egyptian bread maker was making bread for the king. He got lazy and fell asleep. When he woke up the bread was fluffy and collapsible. It was this way because it was left out and yeast landed on it.
Enzymes trigger the chemical change.
It is a change from starch to complex sugars to simple sugars to alcohol. This breakdown is called catalysis. Catalysis can happen in human intestines, which causes pain. The chemical change consists of almost all reactions of physiological importance. Scientist have restricted the things that produce fermentation to a group called ferments that includes molds, bacteria and yeast.