Retention is the coffee that stays inside the grinder after you have finished — trapped in the burr chamber, the chute, and any crevice on the way out. Typical figures run from near zero on hand grinders to several grams on some electric ones.
When it matters
If you single-dose — weighing in exactly the amount you intend to brew — retention is a real problem, and for two reasons.
First, your output does not match your input. Weigh in 18 g and you might get 17 g out, with the difference sitting inside the machine.
Second, and more importantly, what comes out first is what went in last time. If you switched beans, or if yesterday’s grounds have been oxidising overnight, that stale coffee is in today’s cup.
When it does not matter
If you keep a full hopper and grind on demand, retention is irrelevant. The coffee sitting in the chute is the same coffee as the coffee in the hopper, ground a few minutes earlier. Nothing is stale and nothing is mismatched.
That is worth saying because retention is discussed as though it were universally important, and for most people with a hopper it simply is not.
How to reduce it
A puff of air. A rubber bellows into the hopper after grinding pushes most retained grounds through.
A tap. Firmly on the side or the chute. Crude, effective.
The water trick. One spray of water on the beans before grinding — the Ross Droplet Technique — reduces static, which is what makes grounds cling in the first place. It has no measurable effect on the brew.
How much is acceptable
Under a gram is good. Two grams or more is worth working around if you single-dose.
Questions people actually ask
Does retention change the grind size?
Not directly, though a chamber packed with old grounds can affect flow through the burrs. Regular cleaning matters more than the retention number.
Are single-dose grinders worth it?
If you switch beans often or buy small bags of expensive coffee, yes. If you drink one blend from a kilo bag, a hopper is simpler and cheaper.
Last reviewed 8 August 2026