Freshly-ground spices simply taste better than their powdered counterparts, but in order to use freshly-ground spices, one has to actually grind them. If you are the kind of person who has a dedicated spice grinder: Great. I love that for you. But some of us don’t have room for two grinders in our lives. Some of us use our coffee grinders to grind spices.
Coffee grinders do a bang up job grinding whole spices into oblivion, but the flavourful, powdery particulates have a tendency to cling to the insides of your grinder and its blades. Even if you wipe the particulates out with a damp paper towel, oils and other residues can linger, waiting to flavour your coffee. This is not a big deal for certain spices — like cardamom, for instance — but most people do not want their coffee to taste like toasted cumin.
Grinding coffee in your coffee grinder eventually takes care of any off flavours, but you have to sacrifice some coffee. Don’t use the good stuff for this. Good coffee is expensive and should not be use for cleaning, even in pursuit of an off flavour-free grinder. Just use crappy coffee instead.
It doesn’t even have to be crappy beans — crappy pre-ground coffee will work just fine. I use Folgers. I’m not sure if it absorbs or just masks the flavour of the spices, but I do know that I can’t taste them, and that’s the whole goal. After wiping out as much of the ground spices as I can with a damp paper towel, I dump add a couple of tablespoons of crappy coffee into the grinder, grind it for about 3o seconds, then dump that coffee out and wipe the grinder with a damp paper towel once more. After that, my coffee grinder is ready to grind the good beans once more, free from cumin (or anything else).