The Ross Droplet Technique adds a trace of water to beans before grinding to eliminate static.
The concern
People worry that water in a grinder causes rust, clogging or corrosion.
The scale
One or two drops on 18 g of beans is roughly 0.05 g of water — around 0.3% by weight.
Coffee beans naturally hold 2 to 4% moisture, and they absorb more on a humid day. The amount RDT adds is well within the range beans experience naturally.
What actually happens
The water evaporates almost immediately at the burrs, taking the static charge with it. There is no measurable residue.
Grinders in humid climates run damper than this every day of the year.
The real precaution
Do not overdo it. A visible film of water on the beans, or a genuine spray, is too much — that can cause grounds to pack in the chute and, over months, promote corrosion on carbon steel burrs.
Use a fine mist spray bottle, one or two pulses, or stir the beans with a damp spoon handle.
What you get
No spraying, no clinging, dramatically less clumping, and lower retention.
For single dosing it is close to essential.
Alternatives if you are still uneasy
A metal dosing cup, grounding it by hand, and a bellows. They help less.
The consensus
RDT has been used widely for over a decade with no documented grinder damage at sensible quantities.
Last reviewed 8 August 2026