What does light-struck mean?
This is when the beer has been exposed to ultraviolet light for a period of time. Hop-derived molecules, called isohumulones, are basically ripped apart. Some of these parts bind with sulfur atoms to create that skunk character, which is similar in character to a skunk’s natural defense and is such a potent compound that parts-per-trillion can be detected and even ruin a beer. Although brown bottles aid in protecting beer from being light-struck, it hardly makes the beer invincible. Green or clear bottles provide little to no protection. And it’s been said that bottled beer can become light-struck in less than one minute in bright sun, after a few hours in diffuse daylight, and in a few days under normal fluorescent lighting.
This light-struck condition is often to blame for a skunked beer. Many popular imports are distributed in green bottles. Pair the two, mix with misinformation and an inexperienced palate, and the common belief becomes that if beer is in a green bottle, it has to be skunked.
Yeah, but everything I drink from (a green bottled, imported beer) tastes skunked.
Well, it’s not like there’s an international conspiracy by the brewery to expose all of its beer to being light-struck before being sold. Breweries are not in the business to sell spoiled beer. And did you ever consider that that’s the how the beer was intended to smell and taste? The natural and often times wanted sulfur character produced by certain strains of lager yeast, under certain beer style brewing conditions, does not make a skunked beer. Nor does a pungent hop character that you might not be used to. Don’t confuse these characteristics with being skunked, as it’s not always the case.
Yeah, but it’s always skunky in the bottle and not the keg.
Drinking from the bottle is a more concentrated experience. Drinking from a glass allows the beer’s characters to become more volatile, thus a less concentrated experience. It doesn’t necessarily mean that the beer in the bottle is skunked.
How can I avoid skunked beers?
Simple. Don’t buy beer on display, don’t buy beer in a cooler that is brightly lit and don’t leave your beer exposed to light.
So there you have it. Just remember that before you give up on a beer and write it off as being skunked, keep in mind that there’s a lot more that could be going on, and that perception of characters is highly subjective. What you might call skunked due to lack of knowledge could be a tasty German-style Pils to another.