On a recent shopping trip I bought some locally roasted beans from Rwanda, which were labelled "Karenge".

The aroma is delicious, but on opening the bag I immediately noticed light-colored matter clinging to the clefts of the roasted beans (click for close-up):

Karenge beans from Rwanda

Upon grinding light-colored flecks are noticeable in their contrast with the dark coffee grounds.

What is this light-colored matter, and does its presence result from shortcuts in the coffee production or processing?

  • 1
    I don't know if I understand you right. I don't know what kind of information the Suggested Edit review dialog shows you. Maybe you have to switch between the comparison types to see what has changed. I appreciate, that you accepted it anyway. I suggest image-resizing-edits (always using the built in imgur's thumbnail feature) every time I see a big picture. The problem with big pictures is the file size, ergo the loading time of the page. Since resizing the image sometimes makes the content unreadable, I always link to the full size image.
    – Alex
    May 8, 2015 at 13:45
  • @Alex: Okay, the thumbnail loads faster, probably esp. useful for mobile platforms. And a close-up view of the chaff is preserved (even enhanced) in the full-sized version.
    – hardmath
    May 8, 2015 at 13:58

2 Answers 2


What you are likely seeing is the silverskin of the coffee cherry. Green coffee beans prior to roasting generally still have the silverskin intact/attached. As the bean expands during roasting and the silverskin dries out, it generally comes off. Part of the roasting process is some sort of agitation and airflow to remove this chaff. Depending on the roast level and other mechanical factors, more or less of the silverskin may be removed. On lighter roasted coffee with less expansion you can often see bits of silverskin along the seam on the bean. Some processing methods prior to roasting also remove less of the silverskin, "dry processed" coffee in particular tends to be more chaffy when roasting and may require a longer time agitating or smaller roast batches to remove chaff.

Many of my lighter roasts end up with a bit more chaff than I'd like. Like most anything involving coffee, you can find differing opinions on how much it affects taste.


Do you know whether your beans are "washed" ("wet process")?

There should be no problem with the white part. This is typical of washed coffee beans (vs. the "natural" beans that are, well, not washed, and the same part is then black).

Also, when grinding beans, there is production of chaff that does affect the taste of the final drink. This should be the light-coloured flecks you have noticed. Although part of the chaff is inevitable, you can try to remove as much as possible to get better results. Chaff is a reason why a good grinder can be important.

  • 1
    I don't know whether they are "washed", but since the roaster is local, I can ask them (now that you've filled me in) without sounding silly. I've seen this with other whole bean products, but now I have a place to ask about such things!
    – hardmath
    Apr 1, 2015 at 16:29
  • Hahaha, spelling fiend on this one :-) Apr 2, 2015 at 0:06
  • 1
    The label supplied with my "nano-roasted" batch says "wet process", which it dawns on me is the same as your "washed". Good diagnosis!
    – hardmath
    Apr 6, 2015 at 21:43
  • Thank you for the feedback. I did not know that terminology. Added to the answer for ease of reading. Apr 7, 2015 at 0:50

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.