Updated October 2026 · grinding without static
RDT stands for the Ross Droplet Technique: lightly misting your coffee beans with a tiny amount of water just before grinding. It neutralises the static that builds up during grinding, which otherwise makes grounds stick to the burrs and walls and fly around your kitchen.
One or two spritzes of water on your dose, a quick shake, then grind straight away. Less static means less mess, less coffee left in the grinder and fewer clumps. Use it for single doses only.
Why RDT?
Grinding creates friction, and friction creates static. The charged grounds cling to the burrs, the chute and the cup, and spray out of the grinder. A tiny amount of moisture makes the beans conductive enough for the charge to dissipate.
RDT is named after David Ross, who shared it on early online espresso forums in the mid-2000s. It caught on as grinders got finer and static became more noticeable, and it's now a standard tip among home baristas, especially with single-dose grinders.
How to do it
Weigh your exact dose into a small cup or jar.
One or two quick spritzes of clean, filtered water from a fine-mist bottle: just enough for a faint sheen, never a puddle.
Give the cup a gentle shake or stir so the moisture is spread across the beans.
Pour straight into the grinder and grind as usual.
Pair RDT with WDT, stirring the grounds with fine needles before tamping, for an even puck.
A dedicated fine-mist bottle such as the Normcore RDT spray bottle makes it easy to avoid over-spraying. No bottle? Wet the back of a clean spoon and stir it through the dose.
Benefits
Static traps grounds in the grinder, where they go stale and end up in your next dose. RDT gets far more of your dose out, so less waste and fresher shots.
No more grounds flying everywhere. Your counter and grinder stay clean.
Fewer static clumps means a more even bed in the basket, which helps the water flow evenly.
A 2023 study in the journal Matter found that the moisture in the beans controls how much static charge builds up during grinding. A little added water reduces the charge, which means less clumping, and the researchers linked this to more consistent espresso extraction.
See it tested: James Hoffmann's RDT video · Clive Coffee's write-up
Caveats
Moisture and metal can mean corrosion on burrs that aren't stainless. Check your grinder manual before you start.
Too much water gives clumpy grounds. Less is always more: err on the side of dry.
Only spray the dose you're about to grind, never a hopper of beans, where trapped moisture can lead to mould.
Keep reading
Find your starting recipe, then dig deeper into what drives extraction.
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