Chaff is the thin outer skin of the coffee bean and is prevalent in roasted coffee that is of a lighter roast profile, especially if the chaff collector of the roaster becomes full during roasting. When roasted to a darker roast profile, the chaff is burned off of the bean and therefore won’t be present during grinding.
However, the chaff clinging to lighter roasted beans is so thin it is able to pass through the burrs without being reduced in size much, making it more visible in the ground coffee. Chaff isn’t always visible on the whole coffee bean because it’s inside the cleft on the flat side of the bean and is not exposed during roasting.
The light and thin composition of the chaff also makes it prone to static cling where it sticks to the bin and discharge chute. Generating static is inherent to grinding coffee, but we have done our best to combat static by using a grounds bin that is an insulator. Baratza president Kyle Anderson wrote a blog article that provides more detail about static and grinding online here http://www.baratza.com/static-in-your-grinding-its-complex/.