Off Flavors in Beer

I recently took a class to learn more about common off flavors in beer, and thought I’d share the experience with my readers! The sensory analysis class I attended was offered through the Orange County Brewers Guild and focused on seven common off flavors, although there are many more to learn about beyond that. Additional sessions of this OCBG sensory analysis class are still available; tickets are $45 per person, but well worth the price of admission in my opinion. Details on upcoming classes are available at the end of this post for those who are interested in learning more!

As an alternative option, you could purchase the spiking kits online and try this at home, however, the kits are a bit pricey, and I felt that having an instructor available to explain each flavor and answer any questions was very valuable.

Before I go through each of the off flavors, I think it’s fair to note that the base beer we used for each sample was Miller High Life (yes, that’s right, the champagne of beers!). If you’re going to try this at home, I’d recommend starting with a very light, bland lager like this one so that the off flavors have nothing to hide behind. Once you know what to look for though, it would be great to try with other styles to see how those off flavors can change.

The other important thing to mention is that not everyone can taste or smell every off flavor. Some people may not be able to perceive any off flavors at all, so don’t worry if you can’t catch every detail if you try this yourself. Now, let’s get to it!

1.) Acetaldehyde [ac-et-al-de-hyde]

This hard to pronounce compound is acceptable to a degree in some beers, and is often found in very light lagers, especially Bud Light.

Described as:Green-Apple

  • Green apples
  • Carved pumpkin
  • Cut grass
  • Paint


  • Unfinished fermentation

2.) Dimethyl Sulfide (DMS)

DMS is often more perceivable through aroma than taste, but if your base beer is a corn-based lager, it may be harder to spot this off flavor.

Described as:Corn

  • Creamed corn
  • Cooked vegetables
  • Truffles
  • Shell fish
  • Tomato juice (usually in darker beers)


  • Bacterial infection
  • Low pitch rate or unhealthy yeast
  • Lack of proper brewing practice
  • Unfinished fermentation

3.) Isoamyl Acetate [ahy-soh-am-il as-i-tayt]

This ester is produced by yeast, and is present in all beers at different levels. Although it serves as a signature flavor element in certain Belgian and German wheat beers, it may not be desirable in other styles.

Described as:


  • Banana (think banana runts)
  • Pear
  • Circus peanuts


  • Yeast strain/improper yeast management
  • Wild yeast infection
  • Unfinished fermentation (unfortunately, this flavor won’t go away though)

4.) Diacetyl [dahy-uh-seet-l or  dahy-as-i-tl]

This off flavor was one of the easiest to perceive, at least in my opinion. It is a byproduct of some yeast strains, especially English varieties.

Described as:movie-theater-popcorn

  • Buttery (think movie theater popcorn)
  • Butterscotch
  • Oily/slick mouthfeel


  • Contamination, either in the beer or draft lines
  • Bacterial spoilage (Pediococcus or Lactobacillus)
  • Unfinished fermentation

5.) Infection/Contamination

This one is obviously unacceptable in any beer. You may not notice this as much in colder beers, but it becomes more apparent as the beer warms up.

Described as:Vomit Emoji

  • Rancid
  • Bile
  • Stomach acid
  • Sour milk
  • Vinegar
  • Buttery or slick mouthfeel


  • Contamination, either in the beer or draft lines
  • Bacterial spoilage (Pediococcus or Lactobacillus)
  • Improper sanitization

6.) Oxidation

This off flavor is caused when beer is exposed to oxygen at the improper time. Some oxygen will always make its way into beer, but at higher concentrations, it becomes more apparent.

Described as:Cardboard

  • Paper
  • Cardboard
  • Old books
  • Rotten pineapple
  • Dry mouthfeel


  • High storage temperatures
  • Post fermentation aeration
  • Excessive aging

7.) Light Struck

If you’ve ever drank a Corona that’s been sitting in the sun for a few minutes, then this off flavor should be pretty familiar. Be careful when sampling this one – you’ll want to smell the beer from farther away, as you can easily go nose blind to this intense aroma.

Described as:Skunk

  • Skunky
  • Sulfur


  • Exposure to light, usually in clear or green bottles

Besides identifying off flavors, it’s important to try to recognize all favors – intentional or otherwise. When describing beer, I find it helpful to reference the flavor wheel below, which can help you describe the aromas and flavors you’re experiencing.

Flavor Wheel

If you live in or around Orange County, CA and would like to take the class yourself, you can purchase tickets through the links below. The current available date and location options are as follows:

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