What effect does direct sunlight have on beer?

Direct sunlight has a detrimental effect on beer, primarily because it can lead to a chemical reaction that causes a phenomenon known as "skunking." This occurs when UV light interacts with certain compounds in the beer, particularly hops.

When beer is exposed to sunlight or fluorescent light, it can produce a compound called 3-methylbut-2-ene-1-thiol, which gives off a sulfurous aroma reminiscent of skunk spray. This off-flavor significantly diminishes the beer's quality and drinkability, which is why many breweries package their beer in brown or dark bottles to provide better protection against UV light.

The other effects mentioned in the choices do not apply to sunlight's impact on beer. Light does not enhance hop flavors, improve refreshment, or increase shelf life; rather, it damages the beer's taste and overall character. Thus, the correct answer highlights the significant risk that direct sunlight poses to the integrity of beer.