"The hop compounds that are responsible for making beer bitter are called isomerized alpha-acids. These chemicals, along with sulfur compounds found in beer, are also culpable in beer skunking. When ultraviolet light hits beer, it provides the energy necessary to drive a reaction that transforms the iso-alpha-acids into 3-methyl-2-butene-1-thiol. The thiol part of that somewhat cumbersome name indicates that there is sulfur present. Sulfur compounds often have strong, offensive aromas. Some musteline animals, like skunks, have evolved the ability to produce this chemical, and use it for self-defense.
In a sense, the aroma of light-struck beer doesnt just resemble skunk spray, it is skunk spray! Its the same stuff!"