title_body: Light-colored matter clinging to roasted coffee beans
upvoted_answer: 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.