Retention is the coffee left behind in the grinder after grinding — stuck in the burr chamber, the chute and the exit path. It is a small amount, but it has an outsized effect on freshness and consistency.
You will rarely find an official retention figure on a spec sheet, because it depends on technique and is awkward to measure, so it is usually reported by reviewers and users.
Why it matters
High retention means yesterday's stale grounds mix into today's shot, dulling flavour, and it makes your output weight unpredictable — you put in 18g and get 17g of fresh grounds plus a gram of old coffee.
For single dosing this is the whole ballgame: the point of weighing your input is lost if the grinder swallows part of it.
How grinders reduce it
Low-retention designs use short, steep exit paths, bellows to puff grounds out, anti-static measures, and burr geometries that clear cleanly. Adding a little water to the beans (RDT) also cuts the static that makes grounds cling.
Traditional hopper grinders often retain more, which matters less when you grind continuously from a full hopper.
What it means when you're buying
If you single dose or switch coffees often, prioritise a grinder known for low retention — check reviews, since manufacturers rarely publish a number. If you grind from a hopper with one house coffee, retention is a minor concern.
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Frequently asked questions
What counts as low retention?
Roughly a few tenths of a gram or less per dose is considered good. Because it is rarely published, rely on hands-on reviews for real figures.
How do I reduce retention on my grinder?
Use RDT (a spritz of water on the beans), tap or use bellows to clear the chamber, and keep the exit path clean. Design limits set the floor.
Does retention really affect taste?
Yes — trapped grounds go stale and blend into later shots, muddying flavour and skewing your dose. It is most noticeable when switching coffees.