What Is RDT?
The Ross Droplet Technique — named for the home barista who popularized it — involves placing a tiny amount of water (literally one drop, applied with a finger, spray bottle, or syringe) on coffee beans immediately before grinding. The water dissipates the electrostatic charge that forms when coffee beans are ground, eliminating the static cling that causes ground coffee to stick to grinder chutes, portafilters, and itself.
Static in coffee grinding is caused by triboelectric charging — friction between coffee particles and the metal burrs generates charge. The effect is strongest in dry conditions (low humidity, cold weather) and with fine grinds (more surface area, more friction). RDT grounds this charge almost instantly, and the visible result is dramatic: grounds that previously sprayed and clung now fall cleanly.
How to Apply RDT
The dose is minimal — one drop from a damp finger, one spray from a small spray bottle, or 0.3–0.5ml from a syringe. Apply to the beans in the hopper or dosing cup just before grinding. The water disperses across the bean surface during grinding without meaningfully affecting grind behavior or extraction chemistry at this quantity. Using too much water (more than 1–2ml on an 18g dose) can cause coffee to clump in a different way — mud-like clumping rather than electrostatic clumping.
A 50ml spray bottle with water is the most convenient RDT delivery for most home setups — one pump delivers approximately the right amount, no measuring required.
What RDT Improves
Reduced static means: less grounds on the grinder chute walls, less grounds clinging to the portafilter sides and collar, less messy counter workflow, and less clumping before WDT. The last point matters: WDT is still recommended after RDT — RDT reduces clumping but doesn't eliminate the need for WDT distribution. Together, they address static and residual clumping through two complementary mechanisms.
Does RDT Affect Flavor?
At the recommended dose (0.3–0.5ml on 18g), RDT has no measurable effect on extraction or flavor. The water represents less than 3% of the dose weight and is distributed across the bean surface rather than concentrated in any area that would alter extraction chemistry. Multiple controlled comparisons — including one published by the specialty coffee research community — found no statistically significant flavor difference between RDT and non-RDT shots with identical puck prep.
Small Spray Bottle (50ml) for RDT
$A 50ml fine-mist spray bottle holds enough water for weeks of RDT use — one pump delivers the correct amount on beans before grinding.
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One drop or one pump of water on beans immediately before grinding. The result: grounds fall cleanly, less mess, less clumping before WDT. No flavor effect at the correct dose. Use a small spray bottle for the most consistent application.