Why does my grinder clump and throw static everywhere?
Grinding generates a static charge that makes fine particles stick together and cling to everything. A drop or two of water on the beans before grinding, known as RDT, removes almost all of it.
Static in a grinder is triboelectric charging: beans and grounds rub against burrs and chute walls, electrons move, and the resulting charge makes fine particles attract each other and stick to surfaces. It gets worse at espresso fineness because there are more fines, and worse in winter because dry indoor air does not bleed the charge away.
Clumping is the same phenomenon in the basket. Charged fines bind into little balls, and those clumps sit in the puck as dense pockets surrounded by looser coffee. That is the setup for channeling, which is why clumping matters beyond the mess on your counter.
RDT is the fix and it is close to free. Put your dose of beans in a cup, add one or two drops of water, stir for a couple of seconds so the moisture spreads over the bean surface, then grind. The charge dissipates, the grounds come out fluffy and loose, and retention drops at the same time. The quantity is genuinely small: a light mist from a spray bottle is enough for a single dose.
Two questions people reasonably ask. Does it hurt the burrs? A few drops of water on whole beans does not stay on the burrs and does not cause rust in normal use, and this practice has been standard in home setups for years. Does it change the taste? Not detectably at this quantity, and the improvement in puck evenness is far more likely to show up in the cup than the water is.
If you would rather not add water, the alternatives are partial. Grinding into a metal dosing cup rather than plastic helps a little. Anti-static chute mods and grounding wires help on some models. A WDT stir after dosing breaks whatever clumps survive, and if you only do one thing after grinding, do that, since it fixes the puck density problem even when the static problem remains.