What happens to beer when it is exposed to light?

When beer is exposed to light, particularly ultraviolet (UV) light, it undergoes a chemical reaction that produces off-flavors, commonly described as "skunky." This occurs because light interacts with certain compounds in the beer, specifically iso-alpha acids derived from hops, resulting in the formation of 3-methyl-2-butene-1-thiol (MBT), which has an aroma reminiscent of skunk spray. This phenomenon is especially pronounced in beers packaged in clear or green bottles, as these provide less protection against light than brown bottles or opaque cans.

The other options do not accurately describe the effects of light exposure on beer. Light does not improve flavor, enhance carbonation, or increase alcohol content. In fact, these options overlook the significant detrimental impact light can have on the overall quality and taste of the beer, making understanding the skunking effect crucial for beer storage and serving practices.