017. Off-flavor knowledge

Off-flavor knowledge

Beer is a perishable food product. There are many ways that beer can become contaminated before it arrives at your business, or it can just get too old. It is important to be able to identify “off” flavors so you know when to get the customer a replacement.

Although rare, it is possible for beer to become contaminated or damaged before it arrives. Loose seal, inconsistent transportation environment, or poor storage are some ways beer can become damaged or spoiled.

This section helps identify some common off flavors in beer.

The reading material for this section was found in:

RealBeer.com. When your beer really stinks. Beer Break Vol. 1, No. 16. http://www.realbeer.com. Accessed October 3, 2015.

MoreBeer!. “Off” Flavors In Beer; Their Causes & How To Avoid Them. http://www.morebeer.com. Accessed October 3, 2015.


Oxidation means that oxygen has gotten into the beer and made a bad reaction. It can happen during the brewing process, or it can happen later due to poorly sealed packaging.

Oxidation is identified by these aromas and flavors:

  • Stale
  • Old, wet cardboard
  • Paper
  • Pineapple
  • Rotten vegetables
  • Sherry

Oxidation can also make beer bitter or harsh. And it can create aromas and flavors like wax or lipstick.


When light hits the hops in beer, it creates the same chemical in a skunk’s spray.

The reaction happens stronger in light colored beers.

Clear glass and green glass provide almost no protection from light. Amber colored bottles do provide excellent protection, but even amber colored bottles should be stored away from light.

Skunkiness in beer shows up mostly in the aroma.

Skunked beer is identified by these aromas:

  • Skunk
  • Must
  • Burned rubber
  • Cat musk

Dirty draft lines

Recall from lesson 6 “Draft systems” that draft lines must be properly maintained. A perishable food product is traveling through those lines. Make sure the draft lines and other parts of the draft system are cleaned at regular intervals.

Two common signs of dirty draft lines are aromas and flavors of:

  • Butter
  • Vinegar


In the last lesson we talked about the buttery flavor of diacetyl, made by yeast. Diacetyl is usually considered a flaw in lagers, while small amounts are often desired in ales.

Diacetyl can also appear as a contaminant in beer, and especially in dirty draft lines.

Diacetyl is identified in beer by these aromas and flavors:

  • Butter
  • Rancid butter
  • Butterscotch

Diacetyl can also cause a slick mouthfeel.


If the beer has an astringent or sour/acidic flavor that tastes tart or like vinegar, it is likely contaminated by bacteria or wild yeast.

Lambic beers are an exception.

“Lambic style beers,” it says in the MoreBeer! article, “are beers that have been purposely exposed to specific types of wild yeast and bacteria to create the unmistakable cidery and sour flavors they are known for.”


So this is a little bit about how to identify off flavors in beer.

By properly storing your beer products and developing a keen ability to identify off flavors, you have the improved ability to always provide the best beer service to your customers.

So that’s it for Part III. Beer Flavor and Evaluation.

Now we’ll go into Part IV. Beer Ingredients and Brewing Processes.

Flashcards for this section

Based on the reading materials mentioned and my notes above, here are my flashcards for this section.

What is oxidation in beer?

Oxidation is what happens when oxygen gets into beer and makes a bad reaction.

6 aromas and flavors of oxidation in beer

  1. Stale
  2. Old, wet cardboard
  3. Paper
  4. Pineapple
  5. Rotten vegetables
  6. Sherry

Also: bitter, harsh, wax, lipstick

What is “skunked” or light-struck beer?

Beer becomes “skunked” when light hits the hops and creates the same chemical as in a skunk’s spray.

4 aromas of skunked beer

  1. Skunk
  2. Must
  3. Burned rubber
  4. Cat musk

2 flavors from dirty draft lines

  1. Butter
  2. Vinegar

3 aromas and flavors of diacetyl contamination in beer

  1. Butter
  2. Rancid butter
  3. Butterscotch

Also: slick mouthfeel

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    I'm Nathan Pierce. I drink beer, I quit my job, and I'm planning to start a brewery. I also host a podcast about how to start a brewery. So I’m studying for Cicerone® Certification Program, Certified Beer Server exam.

    Study along with me!

    Please note: I reserve the right to delete comments that are offensive or off-topic.

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