Anyone who delves deeper into espresso preparation will inevitably encounter the term channeling. This refers to channel formation in the portafilter, which prevents even extraction and negatively impacts coffee enjoyment.
In coffee forums and video tutorials, you might think channeling is some 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 coffee world – a secret saboteur hell-bent on ruining our perfect espressos!
We advocate for a more relaxed approach to the topic of channeling! In the last 50 years, before bottomless portafilters were used, nobody thought twice about channeling. Yet most espresso brews tasted absolutely delicious and didn't cause anyone any problems.
Since the Third Wave of Coffee and increased interest in the origin and production of coffee, every aspect of preparation has been analyzed more closely and scrutinized. Channel formation in the coffee cake does negatively affect the taste of the coffee, but it can be minimized extremely 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 your espresso.
What happens during channeling from a physical perspective?
During espresso brewing, the brewing water is forced through the coffee cake 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 powder, 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 cake too quickly, the espresso is under-extracted. It then tastes sour and has a watery texture.
By adjusting the grind setting of your grinder, we change the physical resistance to the water. The 9 bars press on the coffee cake and the coffee cake prevents water from getting through. The water wins this battle and the espresso comes out slowly and creamy from the portafilter.
Water takes the path of least resistance. Especially when water is under pressure, it shoots out wherever a small hole appears or a boundary is too thin.
This exact effect happens with channeling. If the coffee cake has a small crack in its surface during grinding, distribution, and tamping, or if a hidden hole is hidden in the cake, the water will take exactly this path during extraction under pressure. Instead of evenly extracting the entire coffee cake in 30 seconds, part of the brewing water shoots directly through this fracture into the cup.
Even though your grind setting might be perfectly adjusted, the coffee is extracted incorrectly at this point in the coffee cake. The areas around the crack in the coffee cake become highly over-extracted, as all the water flows through there. The other areas of the coffee cake become under-extracted. The result in the cup is unbalanced and sometimes barely drinkable.
How do I recognize channeling in my espresso?
If your coffee tastes sour, bitter, or simply unbalanced, it could be a sign of channeling. Of course, there could be other reasons as well. First, we recommend you watch our video on 20 typical mistakes in espresso preparation. If you've avoided all sources of error and your espresso suddenly tastes undrinkable at irregular intervals, that's a clear sign that you occasionally have channeling.
You can recognize channeling even better by looking more closely at the outlet of your portafilter. If the espresso comes out immediately in a dark color and creamy consistency and distributes evenly into two espresso cups, you definitely don't have a channeling problem.
However, if you see very light, almost transparent water coming out at the beginning of the extraction, you can be sure that unwanted channels have formed in the coffee cake. The water then hasn't properly extracted the coffee but has simply flowed past it. It can also happen that a fracture in the coffee cake only breaks open during extraction. In such a case, water gurgles out of the outlets in the middle of the extraction, and the even flow is interrupted. With espresso machines like the Decent or Maro, a faster water flow becomes visible in the graph.
Bottomless portafilter?
However, you can recognize channeling best with a bottomless portafilter. By looking at the underside of the basket, you can see whether the entire coffee is extracted evenly and flows down creamily, or whether there are individual spots where water literally spurts out.
Ideally, espresso flows from the bottomless portafilter initially evenly from all basket holes. Then the espresso comes together into a medium stream in all shades of brown. This looks so good that the espresso must also taste good.
We recognize channeling when thin water sprays break out of the stream and, like from a water gun, spray around the cup and even onto the back wall of the espresso machine. These sprays are often much more watery than the main flow of the espresso.
But be careful: a small spray to the side during extraction doesn't necessarily mean strong channeling. Micro-cracks during extraction always occur. What matters most 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've found that you should be very cautious when searching for traces of channeling. Not every small hole in the coffee cake is a sign of channeling. The escape of CO2, for example, can create superficial holes. Such small, superficial holes don't negatively affect the taste and are completely normal.
However, if you see large holes in your coffee cake that extend from the top to the basket bottom, you can be sure that this channel negatively affected the taste during extraction.
How can I avoid channeling?
Whether you're preparing espresso in a commercial establishment or at home, we show you below classic mistakes that promote channeling. If you avoid these mistakes, you 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 mound forms during grinding. If you now take the portafilter out of the grinder and compress the ground coffee with the tamper, there are spots in the coffee cake where there's much more coffee powder than in others. The coffee cake may look smooth and even at first glance, but under pressure, the water will shoot through the spots where there's less coffee powder, since the resistance is lower there.
Therefore, it's absolutely necessary to distribute the ground coffee after grinding. For example, you can gently tap the portafilter on the work surface to settle the ground coffee. You can also give the portafilter a gentle sideways karate chop. A good WDT tool with good distribution technique is a useful tool for closing underground holes.
Mistake 2: Ignoring your grinder's characteristics
Depending on which espresso grinder you use, different practices are necessary in puck preparation and distribution. In particular, some cheaper grinders clump the coffee heavily at finer grind settings. Others tend to heap the ground coffee more strongly to one side in a tower. When distributing, you should consciously work against these phenomena.
Clumps are a persistent phenomenon that can almost only be broken up with a WDT tool. Wherever clumps are not loosened and instead compressed, 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 advised to tap the tamper against the portafilter one more time after tamping. The idea behind this is that particles stuck to the side of the portafilter by static charge are pushed onto the coffee puck. Don't do this at all! The vibrations break apart the already prepared coffee cake 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 handle it with care. Don't ram 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 cake breaks apart, and channels form that can ruin your espresso enjoyment. Take another two seconds for careful locking and enjoy a perfect extraction!
Mistake 5: Sloppy work
Clean work is one of the most important disciplines in making espresso. You should always rinse the portafilter thoroughly, both to preheat it and to remove old coffee grounds. After that, you must clean out the portafilter. Use, for example, our barista towels for this. Due to the hydrophobic properties of coffee powder, a damp portafilter can promote channeling.
Mistake 6: Using unsuitable dosing cups
Those who like to work with single dosing grinders first grind into a dosing cup and then pour the coffee from there into the portafilter. This 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 can't be closed again to the bottom of the basket, even with the best WDT technique. There are also dosing cups that particularly promote static charge. Others have hard edges at the bottom where the side walls of the cup meet the bottom. This shape then creates an imprint in the ground coffee when it's poured into the portafilter, like a bundt cake mold.
This is why our KM dosing cup is rounded at the bottom and sits on the portafilter with side wings, so it doesn't sink into the cake.
The KM dosing cup is available for 51mm portafilters, which fit Delonghi Dedica machines, for example, as well as for 58mm portafilters.
Other factors that promote channeling
When grinding coffee, the coffee particles become electrostatically charged. The ground coffee doesn't fall homogeneously into your portafilter but often forms small clumps. These are more or less pronounced depending on your grinder. The clumps can make even 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 produce 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 incorrectly adjusted or you stir too aggressively in the ground coffee with the WDT tool, you might end up creating exactly the channels you were 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. The ground coffee is gently stirred with thin needles (0.3–0.5 mm) to avoid channeling and achieve better extraction. Ideally, the movement is slow and even, without vigorously agitating the coffee bed. WDT can be combined with the Ross Droplet Technique (RDT) to reduce static charge already during grinding. After WDT, a leveling tool can be used to level the surface and further optimize extraction.
In our opinion, a leveling tool is more of a visual tool. We've listed the most important steps to prevent channeling 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 a little channeling.
Moreover, you don't need expensive WDT tools, levelers, or even minutes-long "puck preparation routines." Much more important than these things is you, as a confident barista.
Choose 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 snap into the brew group faster than Lucky Luke can draw his Colt.
All these tips can be easily integrated into your workflow, take only a few seconds, and are completely free! Because the most important thing in espresso brewing is you, as a barista!
