“coffee stones” jar
after being picked, coffee is spread out to dry, either in a drying bed, or in some cases, a backyard patio or even along the side of the road.
so you can see how a pebble could get mixed into the coffee. as could little pieces of metal, nut shells, popcorn kernels, feathers, kidney beans, sticks…
any debris that is flammable incinerates in the roaster and is blown out the exhaust. but after the roast, the coffee is dark brown and the stones are gray, so they’re easy to pick out.