The tamp is uneven or sloped
The puck surface slopes visibly, or the shot consistently runs faster on one side than the other.
Applies to: Espresso machine, Espresso
Why a sloped tamp spoils the shot
CoffeeHQ explanation
Tamping does one job: it turns loose grounds into a bed of even depth and even density. Water under pressure flows fastest where the bed is thinnest. If the tamp is sloped, one side of the puck is shallower than the other, and most of the water goes through that side. The shallow side is stripped and turns bitter; the deep side barely extracts and stays sour. The cup has both at once.
How hard you press matters far less than people expect. Once the bed has stopped compressing, more force changes very little. A level tamp at moderate pressure beats a heavy tamp at an angle every time, which is why the work is in alignment, not strength.
Causes, most likely first
There are 4 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 4 · Commonly the cause
Portafilter held in the air or resting at an angle while tamping
- What to change
- Rest it on a flat surface or a tamping mat so the basket is horizontal.
Cause 2 of 4 · Commonly the cause
Wrist not aligned above the tamper
- What to change
- Stand so the forearm is vertically above the tamper and press straight down rather than at an angle.
Cause 3 of 4 · Commonly the cause
Bed uneven before tamping
- What to change
- Distribute and level first; the tamper preserves the bed it finds.
Cause 4 of 4 · Reported, not independently verified
Twisting the tamper on lifting
- What to change
- Lift straight up. Twisting can crack or polish the surface.
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.
- Espresso puck preparation: tamping
- Make my coffee better: Espresso machineEvery reading for this brewer: the check, and the one thing to change first
Support the portafilter, then straighten the wrist
Rest the portafilter on a flat, firm surface with the basket rim level: the edge of the counter, a tamping mat or a stand. Holding it in the air while you press tilts it without your noticing. Stand so that your forearm is directly above the tamper and push straight down, as if pushing a door handle towards the floor. Lift straight up without twisting, and look at the gap between the tamper's edge and the basket rim: it should be the same all the way round.
When the bed was uneven before you tamped
A tamper cannot level a heap. If the grounds fell in a mound on one side, pressing flattens the surface and leaves that side denser underneath, so the puck is level to look at and uneven to water. Distribute first, by stirring and a light tap to settle, then tamp. A tamper noticeably smaller than the basket leaves an uncompressed ring at the wall for the same reason: the tool, not the hand.
Easily confused with
- A channel — A slope makes one whole side flow first and blond early. A channel makes a narrow, fast jet from one point.
- Clumps in the bed — Clumps make density uneven in patches throughout the puck, and no amount of careful tamping removes them.
What not to change at the same time
Do not change tamping pressure and tamping technique together. Fix the level first; pressure is the smaller effect and can be left alone.
How to tell it is fixed
The spent puck is the same thickness all round, and from a bottomless portafilter the whole basket begins to drip at nearly the same moment.
If that changed nothing
If you cannot tamp level by feel, a self-levelling tamper, whose collar rests on the basket rim, removes the skill from the step. It is a legitimate fix for consistency and not an admission of anything.
Related issues
Learn the technique
Step-by-step guides to the skills this problem comes from.