Detecting off flavors in beer is as much of an art as it is a science. It also makes for a fun night of drinking horrible tasting beers with friends. Everyone’s palette is different and some people are super tasters, so people detect off flavors on different levels. What tastes decent to you might taste like complete garbage to someone else. Three beers known for their unique off flavors are Corona, Heinekin, and Redhook ESB.
Off-flavor taste: wet cardboard
Corona frequently suffers from the effects of oxidation and staleness. Oxidation occurs when beer comes into contact with oxygen and is a consequence of age. In order to supersize this effect, expose a Corona to some warm air for a couple hours. You should taste wet cardboard, and harsh, stale, grainy flavors. And no, a lime wedge won't mask the taste of wet cardboard.
Off-flavor taste: skunk
Heineken is known for its green bottles and skunky flavor. Green bottles easily let UV light in. When UV light strikes hop compounds in beer it results in a chemical reaction that causes beer to taste skunky. UV light’s reaction with hops happens instantly. This is why you should never store beer in direct sunlight and should buy beer in brown bottles, as brown glass blocks UV light. To maximize this effect, leave a Heineken bottle out in the sun. You should taste some gnarly flavors.
Off-flavor taste: butter, butterscotch
Redhook ESB is known to have a characteristic diacetyl taste. This off flavor is often described as tasting like movie theater popcorn butter or butterscotch. Diacetyl often results from improper aging, poor yeast health, or bacterial spoilage of beer. In Redhook ESB's case, it’s likely due to the combination of the yeast strain used and the fermentation method employed. Some people find the buttery flavor desirable, which is why Redhook purposefully brews their ESB to be slightly high in diacetyl.