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Specialty Grade A Coffee Defects

Specialty grade coffee is typically used for all high end coffee shops as it reduces the amount of defects that can impacts the taste of the coffee. However, even this coffee has defects that need to be "cleaned" prior to roasting as only one bad coffee seed can ruin the entire cup. Cornerstone Coffee Roasters roasts each batch individually and as a part of our high quality controls we "clean" each roast batch for defects that can ruin or degrade the taste of your cup. Larger roasters are satisfied with the level of speciality grade coffee as it is but you can see in the picture below what may be acceptable by them is not acceptable for us!


Defects can be caused by a multitude of issues, from the processing of the coffee to natural defects in growing the coffee. Although we could spend hours on this we'll highlight some of the issues in the picture below and how it may or may not impact the cup taste.



Specialty Coffee Grade requirements:

  • Specialty coffee uses human and mechanical means to filter out the defects.

  • The SCAA defines specialty coffee in its green stage as coffee that is free of primary defects, has no quakers, is properly sized and dried, presents in the cup free of faults and taints and has distinctive attributes. In practical terms this means that the coffee must be able to pass aspect grading and cupping tests.

Coffee Borer Beetle:

  • A natural cause but separated out due to the major impact on the cup

  • Creates small holes in the coffee seed as it bores into it to lay its eggs. Typically this hole will rot and show a discoloration evident in the pictures below (small black holes) seeds on the right and bottom.

  • Impacts the the cup and should be removed/cleaned out before roasting

  • Farmers can use multiple methods to combat the beetle, natural methods are preferred to eliminate any toxins entering the seeds.

Natural Defects

  • Picking

  • Overripe

  • Dark red to purplish in color (types of coffee will be different in color e.g. red or yellow some is even black)

  • Can impact the cup taste

  • Should be separated visually before processing

  • Seed processing can also help identify and remove

  • Underripe

  • Green in color

  • Under developed

  • Can impact the cup taste

  • Should be separated visually before processing

  • Seed processing can also help identify and remove

  • From the ground

  • Similar to overripe

  • Weather

  • Frost damage

  • Can create malformation of the seeds due to the damage of the outer cherry

  • Possible impact to cup

  • Lack of water

  • Underdeveloped and small seeds

  • Impact to cup taste as it's under developed

  • Processing

  • Machine

  • Smashed seeds

  • No real impact to cup unless damage promotes mold

  • Moisture Content / Drying

  • Lack of proper drying can create mold

  • Mold will definitely impact cup taste!

  • drying to ~11% moisture content minimizes the chance that the coffee will germinate and maintains freshness which in turns maintains cup taste

  • Separation

  • Coffee processing occurs in multiple ways so the below are across methods

  • Remove under/over ripe cherries visually prior to processing

  • Separate by size to eliminate underdeveloped seeds and create a uniform roast

  • Wash channels (wet processed) allow separation by cherry weight - remove the floaters


Coffee defects impact the cost of coffee due to the loss of volume that gets diminished along the way. Specialty grade coffee commands the highest price due to the efforts to grow and process great tasting coffee with very low defects. Coffee that does not meet this standard receives a lower price. Roasters will lose some amount if they "clean" out the remaining defects and then the weight loss from roasting which will be discussed another time.


There are many more defects that can impact the cup but we wanted to highlight a few of the common ones to create an understanding of what goes into each roast at Cornerstone Coffee Roasters.


One other point to note is that green coffee can contain other items that get into the harvest along the way. The below picture shows just a few that we cleaned out from some recent roasts.




If you liked this blog, let us know so we can bring you more of what interests you about coffee!



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