Why does beer sometimes taste like "burnt"?

Sometimes when we drink beer we leave it on the table and after a while we realize that it does not taste the same. It also happens when you buy a cold beer and forget to refrigerate it.

Usually we think it's because it was heated or that it somehow has to do with temperature, but this change in taste is actually due to light.

Ultra-violet radiation, especially from the Sun, causes part of the hops to degrade and give rise to sulfur molecules.

Hop is a plant of the genus Humulus, of the family of the cannabáceas, and is an essential ingredient in the brewing of the beer; Gives a bitter taste by counteracting the sweetness of the malt, and some bacteriological protection.

Sulfur compounds usually have very strong aromas, so once the hops degrade, becoming sulfur, the taste of your drink changes for a much sour. Keeping beer in dark places is the best way to prevent it from getting burned.