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Recognize Defects in Coffee

Learn to recognize some common defects that can possibly arise in your coffee.

Moldy and Damp

  • This is a surface condition on the bean, and would most typically present itself as a powdery, mildew-y type of white material that's certainly not going to be localized to one bean.
  • This defect is not present  in the SCA defect handbook, but is something that if you run into, can be potentially one of the most intense cup defects.
  • This defect can be corrected with a UV sorter. This is a scary defect that you can be saved from.


  • Usually subtle, and presents itself with a sort of artificial chemical cleaning product smell and flavor.
  • There's no visual way to see it and there's no way to remove it. If you happen to come across this in your coffee, you're pretty much out of luck.
  • This defect can be attributed to coffee stored in either a tainted container or in close proximity to other odorous chemicals. This would usually be a result of coffee in its transportation. Coffee is hygroscopic, so it absorbs odors.

Musty and Dusty

  • Musty is almost like a kin or a cousin to moldy, as far as the taste or the flavor.
  • The dusty part can come from storage in dirt, as well as poor processing and poor preparation of the coffee.
  • As this is an absorption type defect, one of the greatest back-ups for coffee is Grainpro or Equitech, or some other type of hermetic bag liner.


  • This presents itself in two different physical defects known as the black bean defect and the sour bean defect.

  • Black is a pitch dark physical manifestation where the pigment is fermented on top of all of these different chemical reactions that have gone onto the bean, often from coffees that have gone overripe that were picked from the ground.

  • The sour defect is more a result of actual over fermentation or slow approach to processing between harvest and process, where, quite literally, the coffee ferments if we don't de-pulp and get it into a controlled fermentation within six to eight, or six to ten hours.


  • This is a fuel-type defect, where people who use substandard jute bags use non food grade diesel as a fixative to fix the fibers.


  • This is a leathery and almost gamy tasting defect, with obvious notes of cooked beef.

  • This is a Maillard -type reaction ,where the reduction of sugar, in combination with protein, essentially creates this type of taste and aromatic sensation.


  • This defect presents itself as a raw rubber flavor. If you've ever been to a rubber plantation or seen or smelled a rubber tree, it's that sort of thing.
  • This defect is more pronounced in espresso, and not as common in high end specialty coffees. This defect presents itself in certain commercial or blender grades quite a bit.


  • This defects presents itself with a rotten potato like taste and you can smell this in the green form of coffee.
  • There has been a lot of conflicting advice over the past 10 years as to where this comes from and how it derives. So far, the biggest preponderance of potato defect you get is in Rwanda, Burundi, and DR Congo. There was a lot of mystery as to what was causing this. Early on, the belief was that it was a fungus. Now, they're saying it's an enzymatic issue. 
  • This is a strong defect, however, if you take UV light, you can see the defect and remove it. 



These are just some of the defects that can arise in coffee.

To view a comprehensive list of defects please refer to the SCA Green Coffee Defect Handbook