Sounds like a wild experiment, but the voltage from a coffee bean root is probably a few millivolts. You could maybe spin a tiny piezo or LED, but a grinder? You’d need a big energy buffer and a high‑efficiency motor. Still, the idea is fun—just make sure the plant gets enough water and sunlight, or it will throw a tantrum. Try a prototype with a small DC motor first and see how many beans you can power.