What I'm curious about is, how many home roasters here have broken their grinder because a stone slipped past?
I have yet to lose a Mazzer to a stone, but they have definitely wreaked some havoc on the burrs. Stones killed my first two decent burr grinders. Actually 3- I killed a Kitcheaid Pro and it's replacement, then a Baratza, and I have pretty much only used commercial grinders since.
It's a real problem with dry-processed Ethiopian coffees. I bet 2/3 of the stones I have found have come out of DP Ethiopians, and most of the rest out of pulped naturals from Central America. It seems to be rarer to find them in Brazils and wet-processed coffees for some reason. I used to have a quart mason jar of "foreign objects" that came out of coffee I handled, but it fell and broke and I was too pissed off to pick through the glass so I just swept it all up and tossed it. My current collection is much smaller. Most of the things I've come across were stones or bits of concrete, but there have been beads, beans, corn, various teeth, nails, desiccated spiders, a gecko, and a little bell. I wish I had kept the human incisor tooth I found, though. I used to wonder how that wound up in there, if the folks sorting the coffee had gotten into a row or something... That came out of some Harrar.
