How do I know if my espresso is channelling?

The shot starts slow, stalls, then gushes; the stream runs off-centre or spritzes; the taste is sour and bitter at once. Cutting the puck open afterwards shows holes or cracks in the bed.

Does tamping harder stop channelling?

No. Pressure above about 15 kg is fully compressed, so force changes almost nothing. A level tamp matters far more than a hard one, and distribution before tamping matters more still.

What is a WDT tool and do I need one?

A WDT tool is a set of thin needles used to stir the grounds in the basket before tamping. It breaks up clumps and evens out density, which removes the most common cause of channelling. A straightened paperclip works almost as well.

Can old beans cause channelling?

Yes. Beans under five days from roast release carbon dioxide that forces channels as it escapes, and beans past eight weeks lose structure and collapse unevenly. Seven to twenty-one days post-roast is the stable window.

Why does my shot start fine then suddenly speed up?

That is the classic signature of a channel opening. The puck holds until pressure finds a weak point, then flow concentrates there. Grind slightly coarser and improve distribution.

Espresso Channelling: Seven Causes and How to Fix Each

You set the ratio, you weigh everything, and the coffee still tastes wrong. In around three quarters of cases the problem is not the recipe, it is the puck. Water takes the path of least resistance, and if the puck has a weak spot, almost all the flow goes through it.

What channelling looks like

A channelled shot starts slow, pauses, then gushes. The stream is off-centre, or it spritzes. In the cup you get sourness from the under-extracted bulk and bitterness from the over-extracted channel at the same time.

Cut the puck open after a bad shot. A channelled puck has holes, cracks, or a visibly lighter core. A good puck is even all the way through.

Ranked causes, most common first

1. Uneven distribution in the basket

Grinding into the portafilter leaves a cone with fines settled in the middle and coarse particles at the edges. Tamp it and you have a density gradient before water even arrives. Use a WDT tool, a small needle stirrer, to break up the pile and level it before tamping. This is the highest-leverage change most people can make, and a paperclip works.

2. A level tamp, not a hard one

Pressure matters far less than level. Anything above about 15 kg is fully compressed, and most people push 10 to 20 kg without realising. A tilted tamp makes an uneven puck no matter the force. Tamp on a level surface and look at the puck from the side before you lock it in.

3. Dose too high for the basket

If the puck touches the shower screen before the shot starts, water has nowhere to go and it drills down. The coin test tells you: dose, tamp, lock in without brewing, remove, and look. A faint shower screen impression is fine. A deep cut-out means you are overdosing.

4. Grind too fine

Very fine grinds have low permeability, so pressure builds until it breaks through somewhere. If your shots dribble, then burst, and the puck is muddy, grind coarser before looking elsewhere.

5. Wrong headspace

Underfilling leaves a water layer on top of the puck that disturbs it before pressure builds. Overfilling leaves no room for the puck to expand. Both create uneven wetting. Match the dose to the basket size printed on it.

6. Stale or very fresh beans

Beans under five days from roast release carbon dioxide, which forces its own channels as it escapes. Beans over eight weeks have lost structure and collapse unevenly. Aim for 7 to 21 days post-roast.

7. Basket quality and machine pressure

Pressurised baskets hide channelling by forcing flow through a valve, which is why they feel forgiving and taste flat. A precision basket makes channelling visible so you can fix it, and stable nine bar pressure keeps the puck intact.

The fixes, in order

Buy or make a WDT tool and use it every shot.
Verify the dose with the coin test.
Level the tamp, forget the force.
Adjust the grinder until the shot runs 25 to 32 seconds.
Use beans 7 to 21 days from roast.

How to tell you fixed it

The stream goes blond evenly, all at once, rather than turning light from one side. Shot times repeat within one or two seconds. The aftertaste is sweet rather than hollow, and sourness and bitterness stop appearing together.

Espresso Channelling