An adjective describing beer that has been ruined by exposure to light. So called because it has the unmistakeable odor of a skunk. The odor is caused when hop resins in the beer react with light to produce mercaptan and related chemicals, the same compounds that give skunks their distinctive aroma. While people who know a little bit about beer will instantly recognize it as a fatal flaw and immediateley dump the offending beverage down the drain, novice beer drinkers, particularly American beer drinkers used to neutral tasting mass-market brews, sometimes mistake it as a sign of quality in imported beers like Heineken and Becks. The defect is quite common in these otherwise fine beers for a few simple reasons, the main one being that the green bottles in which they are sold are transparent to light at the wavelength (~530nm) which causes the chemical reaction that produces the offending mercaptan. This, combined with the fact that they usually are sold from the well-lit display cases of convenience stores and supermarkets (in the U.S.A., at least) gives consumers little chance of getting the quality beer that was put into the bottles at the brewery. The beers mentioned above are supposed to be fairly light in flavor, so if you get one that has an aroma or flavor significantly stronger than the American lager you are used to, dump it, because it is not supposed to taste like that.

Fortunately, there are ways to avoid ever coming across a skunked beer in the first place. For starters, if you must buy a beer from a lighted display, go for one in brown bottles, as it will be better protected against damage from light. Better still, buy beer in cans. It is impossible for beer in cans to ever become skunked. Same thing goes for kegs, which are, after all, simply really big cans. If you just don't feel as suave chugging from a can as you do sipping from a bottle, and you just have to have something that comes in green bottles, buy it in a case which will be better protected from light than the average six-pack.