In the course of your beer drinking life you will be presented with bad beer: bad in the sense that your beer is faulty, presented to you with flavors not intended by the brewer. When presented with said beer, it is your duty to send it back from whence it came. The purpose of this post is to arm you with knowledge on the most common off-flavors so that you are prepared to do the right thing when the time comes.

Bad Beer on Tap

The Brewers Association recommends that tap lines should be cleaned every two weeks. Faucets should be taken apart and cleaned every two weeks as well. Lines should be cleaned with an acid cleaner to remove mineral build-up every three months. Many bars do not follow these guidelines, and the resulting bacterial infections can lead to the following off-flavors:

Sour/Acetic: With the exception of a few beer styles, your beer should not be sour or acetic. This is a sign of lactic or acetic acid in your beer and an infection in the tap lines. Buttery: If your beer smells like movie theater popcorn butter, send it back. A faint butterscotch aroma is appropriate for some English Ales, but in high levels and in other styles, it is indicative of a bacterial infection in the tap line.

Tap line infection is not the only cause for worry. It is also possible that you are being served old beer. If that is the case, you may notice the smell of wet paper or cardboard, an aroma indicative of oxidation.

Bad Beer in the Bottle

Age and improper storage are bottled beers biggest enemies. Generally speaking, bottled beer will keep for around six months if refrigerated and around three months unrefrigerated. This excludes higher alcohol beers and the other beer styles intended for aging. All bets are off if beer is exposed to light or stored at warm temperatures. Here are off-flavors to look for in the bottle.

Skunky: This is probably the most common bottled-beer fault. It is the result of an interaction between light and a compound found in hops. The best protection is keeping your beer bottles out of the light. The next best thing is brown bottles. Green and clear bottles offer little to no protection. If you are served a skunky beer, ask for a different bottle (unless you enjoy the skunkiness).

Oxidized: The same oxidized flavors noted above are commonly found in bottles as well. Pay particular attention to best before or bottled on dates, particularly when buying imported beer.

Autolyzed: If your beer smells meaty or like soy sauce or marmite, this is most likely a result of the death and decomposition of yeast cells in the bottle. In small amounts it can add a certain complexity to higher alcohol beers. In large amounts it can make you feel like you are drinking a glass of soy sauce.

It is also possible to detect the sour or buttery faults noted above in your bottled beer, this is indicative of a bad bottling run resulting in infected bottles (the brewery’s fault). If this is the case, let your server or bottle shop know, and they will, hopefully, pass the news along to the brewery.

Ryan Sloan is an employee at Morgan and York, musician and beer writer. He maintains a personal Web site and can be reached at rysloan4@gmail.