Single dose coffee grinders

A single dose grinder is one you load a shot at a time. You weigh the beans, tip them in, grind, and the machine is empty again. The alternative is a hopper holding a few hundred grams, which is more convenient and means the coffee you drink on Friday has been sitting in a plastic tube since Monday.

Retention is the number the feature is really about

Every grinder keeps some ground coffee inside it between the burrs and the chute. On a hopper grinder that stale residue is the first thing into your next cup. Single dose designs try to get retention close to zero, with steeper chutes, bellows or a knocker, and the good ones publish the figure. It is the specification most makers leave off the box, and it is the one that decides what your first cup of the day tastes like.

It matters most if you own more than one bag

This is the practical case. If you keep a dark roast for milk drinks and a light roast for filter, a hopper means emptying and purging every time you switch. Single dosing makes changing beans a non-event, which is exactly what somebody buying single origin coffee wants.

What it costs you

Time and a scale. Every drink starts with weighing beans, which is fifteen seconds you did not previously spend, and you need something that reads to 0.1g to do it properly. Why a coffee scale needs to read to 0.1g explains the resolution. It is also worse for a household: a hopper grinder is the one somebody else in the house can use without being taught.

Not the same thing as a good grinder

Single dosing is a workflow, not a quality grade. Burr size, burr geometry and how consistently the machine holds its setting decide the cup; single dosing decides how fresh the dose is and how easily you switch. A cheap single dose grinder is still a cheap grinder. Choosing burr or blade is the more fundamental question if you are still on a blade machine.