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.
Pasteurization is a process to destroy harmful bacteria and fungi.
Heating the target liquid to 131-158 degrees does it. A French chemist named Louis Pasteur invented this process. He invented the process in 1865 to inhibit the process of fermentation in juice and milk, because if someone drank fermented juice or milk they could get sick or even die. Ultraviolet light is a part of the electromagnetic spectrum.