Yeuchh! What's wrong with this beer?
I'm not talking about your first taste of a Belgian lambic, a sour beer style with an aroma described as "barnyard" or "wet horse blanket," or the whiff of clove and banana in some traditional wheat beers. These flavors may take some getting used to, but they are appropriate to their respective styles.
No, we're talking about an unpleasant encounter with an old friend.
You go to the supermarket or restaurant, select a beer you have enjoyed in the past and the first sip is a big letdown. There are odd qualities you don't recall from your last pint, or the flavor is missing something special that you once enjoyed.
Please don't turn your back on an old favorite. Although breweries can make mistakes with their beer, it is more likely that your brew has been mistreated somewhere on the perilous trip from the brewery gates to your glass.
There are some common sources of off flavors. If you want to hone your taste buds, you can re-create these flaws on purpose, the way budding beer judges do, and give yourself a mini-tutorial in bad beer. Why would anyone drink bad beer intentionally? Because when you can recognize a defect, your palate is better trained to appreciate a flawless beer. You'll also be a better-informed consumer, able to ask for the quality of service you are entitled to when things go wrong.
When good beers go bad, the most common culprits are light and age. Beer is a fragile beverage, and important flavor components break down with time and neglect. If light can reach beer—in a retail display, especially through clear or green bottles—the result is a beer with a rubbery aroma similar to the telltale scent of a skunk. To replicate the smell, leave a green bottle of light lager in the sun for an hour, and chill it before drinking. Peuuw. Dark brown bottles would pretty much eliminate this problem, but in some breweries the interests of the marketing department seem to trump those of the brewing staff.
If your favorite beer has taken on the character of wet cardboard, old age is the problem. A retailer or barkeep should be mindful of the age of the bottles on the shelves, and the wholesaler should be doubly vigilant. To taste the toll that time takes on beer, buy a bottle covered with dust or one that is clearly beyond its sell-by date, and taste it next to the same beer purchased from a caring retailer. You'll see why beer lovers make such a fuss about freshness.
Beer served on draft should be the freshest pint this side of the brewery. If it's not—if it is bitter in a nasty way, has a sour bite or other off flavors—there may be unwanted beasties lurking in dirty draft lines. This one is hard to re-create at home, but if you get a disappointing glass of a beer that you know should be much better, the housekeeping at your local pub has slipped. Consumers can't police the cleanliness of every bar, but if it were possible, I'd have a sign next to the health department's numerical score listing the last date the draft system was properly serviced.
Even if the draft lines are in great shape, you can be unlucky. Here's a tip from the professional beer consumer: Try to avoid getting the first pint of the evening from a beer tap. Unless the bartender sacrifices the first pour, you'll get the beer that's been sitting, warm, in the tubing since the bar closed the night before.
Of course, there is such a thing as a bad batch, a beer that leaves the brewery in poor shape. A hint of butterscotch is considered appropriate in some ales, but a stronger buttery aroma is a defect. Other brewery problems can contribute essence of cooked corn or Jolly Rancher green apple candy, or the sensation you've just accidentally sucked on a bandage. Or the smell might remind you of strong cheese, sweaty socks or close contact with a goat. These are signs of unhealthy beer.
So, was that disappointing glass of beer the result of rough treatment, a single bad batch or was it just plain bad beer? If you've previously enjoyed the brand, give it the benefit of the doubt: Buy another six-pack, try a different bar or come back next month. If it still disappoints, there are a lot of beers out there still to be tried.