Beer off flavors – how some taste, and common causes

Ever get a papery taste from your beer? It's one of these common off flavors.
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We wrote a story titled "Here's how to tell if the beer you're drinking is any good," after our producer Melissa attended a "beer nerd off-flavor course."

This is a companion list to that story, explaining some of the common off flavors that occur in craft beer – including what to taste for, how it usually happens, and a few thoughts from Melissa.

Read that original story for more on what to do if you notice off flavors.

Acetaldehyde: It smells and tastes like green apple, pumpkin, cut grass, cidery or acidic.

  • Cause: Acetaldehyde is a byproduct of yeast that's produced during fermentation. It's usually turned into alcohol during the fermentation process, but if it doesn't ferment long enough – or not enough yeast is used – it can result in a beer having this acid flavor, Craft Beer and Brewing Magazine explains.

Lactobacillus: It smells and tastes like sour milk or cheese, and kind of buttery.

  • Cause: Lactobacillus is a common bacteria that can get into beer and eat up all the sugars, turning it into lactic acid, which can make the beer taste sour. Keeping things clean during the brewing process helps avoid this from happening. (Note: This isn't always an unwanted flavor in beer – lactobacillus is also a common way to make sour beer.)

Dimethyl sulfide (DMS): Cooked vegetables. This one was a little tougher for a bunch of the people sitting around me in a recent class to smell – some of us could taste it more than smell it.

  • Cause: DMS is byproduct of mashing and fermentation, BeerSmith said, and it's usually naturally boiled off. But if the wort isn't boiled long enough (or correctly), the DMS can't evaporate, which can leave that cooked veggie smell behind. (Note: Low levels of DMS is sometimes desired in lagers.)

Diacetyl: It'll remind you of butter or butterscotch, and many people will get it confused with a beer that has lactobacillus – but the difference is this one feels more slick in your mouth.

  • Cause: Diacetyl is naturally produced by yeast during fermentation, and then is re-absorbed, but this may not happen if mistakes are made during the process, MoreBeer.com explained. You can also get this taste if you're having a pint at a bar that hasn't cleaned its tap lines for awhile.

Isovaleric acid: Smells just like hockey equipment you haven't washed in awhile, and it was really hard to get the nasty, old hops taste out of your mouth. (In my opinion this was the worst tasting and smelling sample of the night.)

  • Cause: That old hop taste is caused by – you guessed it – old hops. If a brewery doesn't use hops fast enough, it gives it this awful flavor and smell.

Light-struck: This one is something many beer drinkers have come across – a skunked beer. It tastes and smells skunky, or kind of like toffee or coffee.

  • Cause: UV light. If the beer you bought has been sitting under the bright lights at a liquor store too long, you'll get that skunky flavor in your beer. Note: Brown bottles are the best at blocking UV light (they block about 97 percent, so can sit under lights or in the sun for a few hours without getting skunked). Green bottles only block 30 percent of UV light. Those clear bottles – they block 0 percent of UV rays, so they can get "skunked" instantly. (Not everyone hates this flavor thought – think of Heineken and Corona, they sell a lot of beer.)

Metallic: This one was hard to smell, but boy did it taste like tin or like you bit your tongue and it was bleeding.

  • Cause: Metal – it can happen when at some point during the brewing process the beer comes into contact with something metal. Craft Beer and Brewing Magazine has more on this. One thing to know is this flavor does not come from cans – at least not anymore. Cans are now made with a lining that prevents that penny flavor, Vine Pair explained.

Oxidation: Smells just like cardboard or a yellow legal pad – and has a very papery taste.

  • Cause: Oxygen. When it comes into contact with beer, it degrades the flavor. It's another one of the most common off flavors beer drinkers will come across, so just make sure you're drinking fresh beer. The longer it sits on the shelf, the more oxygen can seep into your beer. (Oxygen can also get into a beer if its not bottled, canned or fermented correctly.)

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