Mr Wort Hog has been talking about becoming BJCP-certified for a while now, and recently signed up for an exam sitting in January. We've been accumulating study materials as a result: books, articles, and - of course - beer. I'm not taking the exam, but I am learning more about beers as he studies them and we discuss them. While it's fun to try standard examples of styles and note their qualities, there's another aspect of studying that I'm finding particularly fun: detecting off-flavors.
You can easily create most off flavors yourself with a handful of common household ingredients (and a few extra available at a homebrew store). I picked up a six-pack of Sam Adams Light, since the base beer for doctoring should be pretty clean & light - and must have a pry-off crown cap. Guidelines for modifying beers with off flavors are listed on the BJCP site in a handy table. Want to see what an oxidized beer tastes like? You could add 3/4 of a teaspoon of sherry to a 12oz bottle of beer, or simply oxidize the beer by opening it, allowing the CO2 to escape, re-capping it, and storing it at over 100F for a few days. How about a skunky beer? Set a beer (in a green or clear bottle) in a window for a week. (Or, buy a bottle of Grolsch).
I've been doctoring up the bottles & presenting glasses containing the adulterated (and some unadulterated!) beer to Mr Wort Hog for his analysis. It's been fun and a good learning experience. The biggest take-away so far has been that off flavors are most easily detectable when you let the beer warm up (to maybe 55-60 degrees) then swirl it around in your glass. The swirling releases some of the CO2 from the beer, carrying the aroma out of the beer and around the mouth of the glass. And for anyone who has had warm beer, you'll know that when it's warm, the flavor is intensified. (Similarly, I'm sure that's why a lot of people like ice-cold beer - you can't taste it.)
If you're evaluating or reviewing a beer, you'll also want to know if what you're tasting is really an off flavor. If you have a beer that has just a hint of sherry, is that always a bad thing? If it's a Pale Ale, it shouldn't be there - but it can actually add depth and complexity to a Barley Wine. Dimethyl Sulfide (DMS) adds a cooked veggie characteristic to beer, and a little bit is just fine in, say, an American Lager like Budweiser. If you've had a Schlitz Gusto and thought that there was a little roasted corn flavor - that's DMS. But what if your beer tastes buttery? Medicinal? Like almonds? BJCP has answers. Additionally, a great explanation of these flavors can be found on John Palmer's website, or in his book of the same title.
Off flavors are, unfortunately, pretty easy to introduce to beer but can be avoided with some care. For homebrewers, the main concepts are simple (sanitation, fermentation temperature, avoiding exposure to oxygen after fermentation starts, etc) but the details are endless. I still have trouble remembering everything and have a long way to go.
There are also some things we can do as consumers of beer, starting with avoiding beer in clear bottles or the ones near the window at the liquor store, and storing our beer in dark, cool locations of the house (say, the fridge). I know I have been guilty of lazily leaving a six-pack on the back porch in the dead heat of summer. Beer nerd fail!