Channeling is when water finds a weak spot in the coffee puck and rushes through it instead of flowing through all the coffee evenly. Part of the coffee gets over-extracted, the rest barely gets touched, and the shot tastes sour and bitter at the same time.
How to tell it's channeling
- The shot runs fast even though your grind setting hasn't changed.
- It tastes sour and bitter at once, or just thin.
- The used puck is wet and soupy, or has a small hole or crack in it.
- With a bottomless portafilter: spurts, sprays, or one pale patch that appears early while the rest is still dark.
Why it happens on a Barista Express
The built-in grinder is convenient, but at espresso settings it drops clumps, and the coffee tends to pile up on one side of the basket as it falls from the chute. Clumps and uneven piles leave dense spots and loose spots. Water takes the loose route. A tamp that's slightly tilted does the same thing.
The fixes, in order
1. Stir the grounds
This fixes more channeling than anything else. Stir the coffee in the basket with thin needles for 10 to 15 seconds, breaking every clump, then smooth the top. That's all a WDT tool does. A straightened paperclip works if you want to try it free first.
2. Level before you tamp
Tap the side of the portafilter a couple of times so the bed settles flat. You want the same depth of coffee everywhere.
3. Tamp level, not harder
Tamping harder doesn't fix channeling. Tamping straight does. The Barista Express portafilter is 54mm, but the basket inside it is about 53mm, so it takes a 53mm tamper. A tamper that fits snugly, or one with a depth collar that rests on the rim, makes a level tamp automatic.
4. Check the dose
Too little coffee leaves the puck loose and easy to break through. Aim for about 18g in the double basket, or use the Razor tool to trim it to the same height every time.
5. Then the grind
If the shot still runs fast after all of the above, grind finer. Here's where to start on the Barista Express grind dial.
What doesn't fix it
- Tamping harder. Past a firm, even press, extra force changes very little.
- A puck screen. It helps keep the shower screen clean. It doesn't stop channeling that starts in the coffee bed.
- The dual-wall basket. It hides channeling rather than fixing it.
The short version
Stir, level, tamp straight, same dose every time. That's the whole routine, and it takes about a minute. Here it is step by step.
Every tool we sell that fits the Barista Express is on one page: Everything for your Barista Express. Tell us your machine. If it doesn't fit, we'll make it right.