How to Taste What You Shouldn't be Tasting: Green Apple
Welcome to ABV's field guide to off-flavor tasting, or what I like to call how to taste what you shouldn't be tasting. If you missed part one, diacetyl, you can find it here. Today's topic is beer that tastes like green apple.
As many of my readers know, off-flavors, are unpleasant flavors in a batch of beer. These tricky little jerks arise from a number of sources, but mainly are due to a process or recipe issue – too high a percentage of roasted malt, improper sanitation – or a fermentation problem like pushing yeast too far, or fermenting at too warm a temperature. Off-flavors are acceptable or even desired in certain amounts in particular styles of beer – phenols in hefeweizen, DMS in cream ale. In those scenarios, they would not be dubbed "off." It is always good to consult the BJCP style guideline regarding what is appropriate. However, they make themselves known when they are out of place, and they seem to be garnering the interest of more and more people.
In the past few years, I have found more beer enthusiasts, not just beer professionals, seeking information about fermentation flaws in the form of off-flavor classes and tastings. Tastings of intentionally flawed beer for learning purposes are sometimes called "spiked" tastings. If you have the opportunity to attend one, I highly recommend it.
Today we chat about a flavor that should never be perceptible in beer: green apple, which may also strike the palate as apple candy or apple skin. I say "never" because Randy Mosher says never, and I am not inclined to disagree with him, but the BJCP states that a light apple character is not a flaw in Light American Lagers and American Lagers.
Unlike other flavor compounds that are sometimes acceptable on a style-by-style basis, intense green apple is uniquely undesirable across the board. Can you recall drinking a lager with a strange cider-like aroma or flavor? Perhaps not recently, but now that you're armed with this vocabulary, I'd be willing to bet you will notice it in the near future, with the return to taprooms after months of home drinking.
Acetaldehyde is the chemical compound that is responsible for the true Granny-Smith-meets-Dum-Dum-sucker flavor. We are talking about what some people would call "green" flavors, and that descriptor is quite appropriate as the problem typically arises from "green" beer -- that is, beer that has not properly conditioned or rested. It is rare to find acetaldehyde in properly-made beer that was not forced to market too quickly.
Yeast make acetaldehyde during their conversion of sugars to ethanol and carbon dioxide (the natural carbonation found in some naturally-carbonated beers, or blown off the fermentation tanks in most cases). The reason it can be found in young, incomplete beers is because this byproduct is eventually consumed by the yeast if they are allowed to do so.
Thus acealdehyde can also arise from underperforming yeast who fail to fully complete fermentation and clean up after themselves (such is also the case with diacetyl). Advice for brewers is simple: keep the wort in contact with healthy yeast and give it adequate time. Of course there are nuanced problems and solutions, as well, but this basic advice will go a long way.
Drinking a beer with an unacceptable amount of green apple flavor? Tell your bartender respectfully and objectively, pass it off to a friend with the palate of a city raccoon, or do your best to enjoy it before ordering another round. you've learned something -- you will know what you are tasting and why. Cheers!