Anyone who gets more intensively involved in espresso preparation will inevitably have to deal with the concept of channeling. This refers to channel formation in the portafilter, which prevents even extraction and negatively affects coffee enjoyment.
In coffee forums and video tutorials, you might think channeling is the evil monster lurking in the closet, just waiting to sneak around the corner and turn our beloved coffee into a bitter or sour nightmare. It seems as though channeling is the root of all evil in the world of coffee – a hidden saboteur bent on ruining our perfect espressos!
We advocate for taking a relaxed approach to channeling! In the last 50 years, before bottomless portafilters were used, nobody gave any thought to channeling. Yet the vast majority of espresso brews tasted absolutely delicious and nobody complained.
Since the Third Wave of Coffee and the more intense interest in the origin and production of coffee, every aspect of preparation is being analyzed and scrutinized more closely. Channel formation in the coffee puck negatively affects the taste of the coffee, but it can be extremely minimized through simple steps! In our blog, we show you why channeling actually affects taste, how to recognize channeling in your espresso, and what mistakes you should avoid when preparing espresso.
What happens during channeling from a physics perspective?
When brewing espresso, the brewing water is forced through the coffee puck and portafilter at approximately 9 bar pressure. As you already know, the extraction time of the espresso decisively determines the taste of the espresso. The longer the water is in contact with the ground coffee, the more particles are extracted from the coffee. If the coffee is extracted too long, it becomes over-extracted, tastes bitter, and has an unpleasant mouthfeel. If the water runs through the coffee puck too quickly, the espresso is under-extracted. It then tastes sour and has a watery texture.
By adjusting the grind size of the grinder, we change the physical resistance for the water. The 9 bar pressure pushes on the coffee puck, and the coffee puck prevents the water from coming through. The water wins this battle, and the espresso comes slowly and creamily from the portafilter.
Water takes the path of least resistance. Especially when water is under pressure, it hisses out wherever a small hole opens up or a boundary is too thin.
This exact effect happens during channeling. If the coffee puck has a small crack in its surface from grinding, distribution, and tamping, if there's a hidden hole in the puck, the water will take exactly this path during extraction under pressure. Instead of evenly extracting the entire coffee puck in 30 seconds, part of the brewing water shoots straight through this break into the cup.
Even though your grind size might be perfectly set, the coffee is extracted incorrectly at this point in the coffee puck. The areas around the crack in the coffee puck are extracted very heavily because all the water flows through there. The other areas of the coffee puck are under-extracted. The result in the cup is unbalanced and barely drinkable in some cases.
How do I recognize channeling in my espresso?
If your coffee tastes sour, bitter, or simply unbalanced, that could be a sign of channeling. Of course, there could be other reasons. First, we recommend watching our video with 20 typical espresso preparation mistakes. If you've avoided all sources of error and your espresso tastes undrinkable at irregular intervals, then that's a clear sign that you occasionally have channeling.
You can recognize channeling even better if you look closely at the outlet of your portafilter. If the espresso comes out directly in a dark color and creamy consistency and distributes evenly across two espresso cups, then you definitely don't have a channeling problem.
However, if you see that very light, almost transparent water comes out at the beginning of extraction, you can be sure that unwanted channels have formed in the coffee puck. The water then didn't extract the coffee properly, but simply ran past it. It can also happen that a crack in the coffee puck breaks open during extraction itself. In such a case, water bubbles out of the outlets in the middle of extraction, and the even flow is interrupted. With espresso machines like the Decent or Maro, a faster flow of water is then visible in the graph.
Bottomless portafilter?
The best way to recognize channeling, however, is with a bottomless portafilter. By looking at the underside of the screen, you can see whether the entire coffee is extracted evenly and flowing creamily, or whether there are individual spots where water is practically squirting out.
Ideally, the espresso flows out of the bottomless portafilter evenly from all screen holes. Then the espresso gathers into a medium stream in all shades of brown. That looks so good that the espresso must taste good too.
We recognize channeling when thin water spritzers break out of the stream and, like with a water gun, spray around the cup and even land on the back wall of the espresso machine. These spritzers are often much more watery than the main flow of the espresso.
But be careful: a small spritzer to the side during extraction doesn't necessarily mean strong channeling. Micro-cracks during extraction always occur. What's most important is always the result in the cup.
Is it worth reading coffee grounds?
There are supposedly people who can even predict the future from coffee grounds. However, we have found that you should be very careful when searching for clues about channeling. Not every small hole in the coffee puck is a sign of channeling. For example, CO2 escape can also create superficial holes. Such small, superficial holes don't negatively affect taste and are completely normal.
However, if you see large holes in your coffee puck that extend from the top to the screen bottom, then you can be sure that this channel negatively affected the taste during extraction.
How can I prevent channeling?
Whether you're preparing espresso in a commercial operation or at home, we'll show you classic mistakes that promote channeling. If you avoid these mistakes, you'll significantly reduce the risk of channeling!
Mistake 1: Tamping without distributing
The ground coffee doesn't land evenly from the grinder into the portafilter. There's always a spot in the portafilter where a small coffee mountain forms during grinding. If you now remove the portafilter from the grinder and compress the ground coffee with the tamper, there are places in the coffee puck where there is much more ground coffee than in others. The coffee puck may look smooth and even at first glance, but under pressure, water will shoot through the places where there is less ground coffee, as resistance is lower there.
That's why it's absolutely necessary to distribute the ground coffee after grinding. For example, you can gently tap the portafilter on the work surface to allow the ground coffee to settle. You can also nudge the portafilter with gentle, sideways karate moves. A good WDT tool with good distribution technique is a good way to close underground holes.
Mistake 2: Ignoring the peculiarities of your grinder
Depending on what espresso grinder you use, different practices are needed in puck preparation and distribution. Some cheaper grinders especially clump the coffee heavily at finer grind sizes. Others tend to heap the ground coffee more to one side in a tower. When distributing, you should consciously work against these phenomena.
Clumps are a stubborn phenomenon that can almost only be broken up with a WDT tool. Wherever clumps aren't loosened and are pressed instead, a breaking point for the brewing water almost always forms.
Mistake 3: Tapping the tamper against the portafilter
In some courses or internet tutorials, you're recommended to tap the tamper against the portafilter once more after tamping. The idea is that particles stuck to the edge of the portafilter by static charge get shoved onto the coffee puck. Don't do this under any circumstances! The vibrations break up your already prepared coffee puck and create channels, especially at the edge of the portafilter, through which water shoots.
Mistake 4: Too much speed when locking in
Even if it looks cool: when you lock in the portafilter, please treat it carefully. Don't jam it abruptly into the brew group – after all, you're not loading a revolver! If you bang the portafilter against the brew group, it has the same effect as tapping with the tamper. The coffee puck breaks up and channels form that can spoil your espresso enjoyment. Instead, take a couple extra seconds for careful locking in and enjoy perfect extraction!
Mistake 5: Sloppy technique
Clean technique is one of the most important disciplines when making espresso. You should always rinse the portafilter thoroughly, on one hand to preheat it, and on the other hand to remove old coffee grounds. After that, you need to wipe out the portafilter. For example, use our barista cloths . Due to the hydrophobic properties of coffee grounds, a damp portafilter can promote channeling.
Mistake 6: Using unsuitable dosing cups
If you like working with single dosing grinders, you first grind into a dosing cup and then pour the coffee from there into the portafilter. It sounds trivial, but it's a step that, especially with poor dosing cups, provokes significantly more channeling than grinding directly into the portafilter.
Poor dosing cups sink completely into the portafilter and leave a crater at the edge that even the best WDT technique can't close all the way to the bottom of the screen. There are also dosing cups that promote strong static charge. Others have hard edges at the bottom where the cup's side walls meet the bottom. This shape then leaves an impression in the grounds, like a cake mold, when it's poured into the portafilter.
This is why our KM dosing cup has a rounded bottom and sits on the portafilter with side wings, so it doesn't sink into the puck.
The KM dosing cup is available for 51mm portafilters, which fit machines like the Delonghi Dedica, as well as for 58mm portafilters.
Other factors that promote channeling
When grinding coffee, the coffee particles are charged electrostatically. The ground coffee doesn't fall homogeneously into your portafilter, but often forms small clumps. These are more or less pronounced depending on the grinder. The clumps can make homogeneous tamping difficult in the portafilter. If your grinder produces such large clumps, you can try to destroy them by tapping the portafilter on the table surface or with a so-called WDT tool to create homogeneous ground coffee.
However, the problem with many espresso gadgets is that they need to be used correctly and adjusted well. If a leveler tool is set incorrectly or you dig too hard in the coffee grounds with a WDT tool, you might end up creating exactly the channels you were actually trying to avoid.
How to do WDT
The Weiss Distribution Technique (WDT) was developed by John Weiss to dissolve coffee clumps in the portafilter and ensure even distribution before tamping. This involves gently stirring the ground coffee with thin needles (0.3–0.5 mm) to avoid channeling and achieve better extraction. Ideally, the movement is slow and even, without vigorously disturbing the coffee bed. WDT can be combined with the Ross Droplet Technique (RDT) to reduce static charge during grinding. After WDT, a leveling tool can be used to level the surface and further optimize extraction.
However, a leveling tool is in our view more of a visual tool. We've listed the most important steps to prevent channeling further above.
Conclusion: The most important thing in espresso is the barista
It's very difficult to completely avoid channeling 100% of the time. And as we told you in the introduction, espresso can taste delicious even with small amounts of channeling.
Furthermore, you don't need expensive WDT tools, levelers, or lengthy "puck preparation routines." Much more important than these things is you, as a confident barista.
Decide on a good and solid grinder. When filling the portafilter, make sure the ground coffee can settle well and doesn't form mountains. Tamp straight and don't let the portafilter shoot into the brew group faster than Lucky Luke can draw his Colt.
All these tips can easily be integrated into your workflow, take only a few seconds, and are completely free! Because the most important thing when brewing espresso is you as a barista!
Channeling is one of several points where a shot can go wrong. You'll find the complete process in preparing espresso.
