The grinder holds on to coffee between doses
Less coffee comes out than went in, and the first dose after a change of bean tastes of the previous one.
Applies to: Espresso machine, Espresso, Filter coffee
Where the missing coffee goes
CoffeeHQ explanation
Between the burrs and the outlet of a grinder there is space: the chamber around the burrs, the exit chute, and often a flap or screen. Ground coffee fills that space and a portion stays there when the motor stops. This is retention. Some of it is exchanged with every dose, so each dose is partly coffee from the last grind, and some of it sits for days.
Retention causes three separate problems, and it helps to know which one you have. The dose that comes out is lighter than the beans that went in. The first coffee out after a pause is stale, because it has been sitting ground and exposed. And after a setting change, the next dose is a mix of two grind sizes.
Causes, most likely first
There are 3 likely causes, listed with the most probable first. Work down the list and change one thing at a time, so that when the problem goes away you know which change fixed it.
Cause 1 of 3 · Commonly the cause
Coffee held in the chute and around the burr carrier
- What to change
- Clear the chute with a bellows or brush after each dose, and weigh the ground coffee rather than the beans.
Cause 2 of 3 · Reported, not independently verified
Static holding grounds against the grinder's internal surfaces
- What to change
- Reducing static reduces what stays behind. The grinder flows on the grind-size guide set out the options, and what one study found about a little water on the beans.
Cause 3 of 3 · Commonly the cause
A grinder design that retains a great deal by nature
- What to change
- Some grinders retain far more than others. Where the amount is consistent, compensate by weighing the output.
If none of these fixes it
Check the cleaning and descaling guide. Equipment that needs maintenance can cause several of these symptoms at once, and no change of recipe will correct it.
Work through it for your setup
The causes above are general. These go to the part of a diagnostic that takes this symptom one check and one change at a time.
- Less coffee comes out than went inThe possibilities, the quickest check and one thing to change first
- The first cup of the day tastes flat, or of the last coffeeThe possibilities, the quickest check and one thing to change first
Weigh what comes out, not what goes in
Put the basket or dosing cup on the scale and weigh the grounds. Whatever the grinder kept, you now know the real dose, and that removes the first problem completely. For the second, purge a couple of grams before the first shot of the day and after changing the setting. A few taps on the body of the grinder, or a puff from a bellows if it has one, clears the chute.
A grinder with a hopper is meant to retain
Grinders built to work from a full hopper keep the grinding path charged with coffee by design, because that gives a steady feed and a consistent dose in a busy café. Used at home for two shots a day, the same design means the coffee in the path goes stale between uses. That is a mismatch between the tool and the job, and purging is the cost of it. Single-dose grinders are designed the other way, to pass everything through, at the price of a less convenient workflow.
Easily confused with
- A dose that varies — Retention that is the same every time is easy to live with. Retention that varies is what makes the dose unpredictable, and weighing the output fixes both.
- Stale beans — If only the first shot of the day tastes flat and later ones are fine, the stale coffee was in the grinder, not the bag.
What not to change at the same time
Do not start purging and change the grind in the same session if you are trying to learn what retention was doing. Purge first, at an unchanged setting, and see what alters.
How to tell it is fixed
The weighed dose in the basket is within a few tenths of a gram of what you intended every time, and the first shot of the day tastes like the second.
If that changed nothing
If output still falls well short of input after tapping and purging, look for packed coffee behind the chute or around the burr carrier. Clean it as the manufacturer describes; a blocked chute can hold a great deal.
Related issues
Work it out
Interactive tools that take you through this one change at a time.
Learn the technique
Step-by-step guides to the skills this problem comes from.
- Purging a grinderClear coffee left inside the grinder so the next dose is the coffee and the setting you intended.
- Single dosing a grinderGrind exactly the beans you weighed for this brew, with as little left inside the grinder as possible.
- Cleaning a grinderRemove built-up coffee oils and retained grounds without damaging the burrs.