The dose from the grinder varies shot to shot
Grinding the same amount by time or by the same number of turns produces a different weight of coffee each time.
Applies to: Espresso machine, Espresso
Why a timed dose drifts
CoffeeHQ explanation
A grinder with a timer delivers coffee for a number of seconds. It does not deliver a weight. How many grams leave in those seconds depends on how fast beans feed into the burrs, and that changes with the weight of beans pressing down in the hopper, with the grind setting, with the roast and density of the coffee, and with how much was left in the chute from the previous dose. Timed dosing is consistent only while every one of those holds still.
In practice the dose from a nearly empty hopper is lighter than from a full one, a finer setting delivers less per second than a coarser one, and a new bag changes everything. A drift of a gram is ordinary, and a gram is enough to move an espresso shot by several seconds.
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
Grinding by time rather than by weight
- How to check
- Are you dosing by a timer rather than a scale?
- What to change
- Seconds are a proxy for grams, and the relationship shifts with grind setting, bean age and roast. Weigh instead.
Cause 2 of 3 · Reported, not independently verified
Variable retention between doses
- What to change
- Purge the chute consistently, and weigh the output rather than the input.
Cause 3 of 3 · Reported, not independently verified
Hopper level changing the feed rate
- What to change
- A nearly empty hopper feeds more slowly than a full one. Keep the level roughly consistent, or single dose.
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 same setting gives different results from day to dayThe possibilities, the quickest check and one thing to change first
Dose by weight, in whichever way suits the grinder
The fix is to stop trusting time. With a single-dose workflow, weigh the beans, grind them all, and weigh the grounds once to learn what the grinder keeps. With a hopper, grind a little over the target into a cup on a scale and remove the excess, or grind short and top up. Either takes a few seconds and removes the largest source of shot-to-shot variation that most home setups have.
Easily confused with
- A grind change that misbehaved — If shot time wanders at a setting you have not touched, look at the dose before the grind. A timed dose changes whenever the setting does.
- Retention — Retention is one of the reasons a timed dose varies. Weighing the output corrects for it without your needing to measure it.
What not to change at the same time
Do not re-set the timer and the grind setting together. Changing the grind changes the grams per second, so the timer has to be re-checked after every grind adjustment anyway.
How to tell it is fixed
Five consecutive doses weighed in the basket fall within about two tenths of a gram of each other, and shot times at a fixed setting tighten up as a result.
If that changed nothing
If weighed doses are consistent and shot times still wander, the variation is in the puck. Look at distribution and tamping next.
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.