Anyone who delves deeper into espresso preparation will inevitably encounter the term "channeling." This refers to the formation of channels in the portafilter, which prevents even extraction and negatively impacts the coffee experience.
In coffee forums and video tutorials, you might almost think that channeling is a malicious monster in the closet, just waiting to sneak around the corner and turn our beloved coffee into a bitter or sour nightmare. It seems as if channeling is the root of all evil in the world of coffee—a secret saboteur hell-bent on ruining our perfect espressos!
We urge you to remain calm when it comes to channeling! In the past 50 years, before bottomless portafilters were used, no one gave channeling a second thought. And yet, the vast majority of espresso brews tasted delicious and didn't knock anyone's socks off.
Since the third wave of coffee and the increased interest in the origin and production of coffee, every aspect of preparation is being analyzed and scrutinized more closely. Channeling in the coffee cake negatively impacts the taste of the coffee, but it can be greatly minimized with simple steps! In our blog, we'll show you why channeling actually affects the taste, how to recognize channeling in your espresso, and which mistakes you should avoid when preparing espresso.
What happens during channeling from a physical perspective?
When brewing espresso, the brewing water is forced through the coffee cake and portafilter at approximately 9 bar of pressure. As you already know, the extraction time of the espresso determines its flavor. The longer the water is in contact with the ground coffee, the more particles are extracted from the coffee. If the coffee is extracted for too long, it is over-extracted, tastes bitter, and has an unpleasant mouthfeel. If the water passes through the coffee cake too quickly, the espresso is under-extracted. It then tastes sour and has a watery texture.
By adjusting the grinder's grind size, we change the physical resistance to the water. The 9 bars press against the coffee cake, which prevents the water from passing through. The water wins this battle, and the espresso emerges slowly and creamily from the portafilter.
Water seeks the path of least resistance. Especially when water is under pressure, it hisses out wherever a small hole opens up or a barrier is too thin.
This is precisely the effect that occurs with channeling. If the coffee cake develops a small crack in its surface during grinding, dispensing, and tamping, or if there's a hidden hole in the cake, the water will take exactly that path during the pressurized extraction. Instead of evenly extracting the entire coffee cake in 30 seconds, a portion of the brewing water will shoot through this crack into the cup.
Even though your grind may be perfectly adjusted, the coffee is being extracted incorrectly at this point in the coffee cake. The areas around the break in the coffee cake are being extracted very heavily because all the water flows through there. The other areas of the coffee cake are being underextracted. The result in the cup is unbalanced and, in some cases, barely drinkable.
How do I recognize channeling in my espresso?
If your coffee tastes sour, bitter, or simply unbalanced, this could be a sign of channeling. Of course, there can be other reasons as well. First, we recommend watching our video with 20 common espresso brewing mistakes. If you've avoided all possible mistakes and your espresso suddenly tastes undrinkable at irregular intervals, this is a clear sign that you're occasionally experiencing channeling.
Channeling is even easier to spot if you take a closer look at the spout of your portafilter. If the espresso comes out dark and creamy and is evenly distributed between two espresso cups, then you certainly don't have a problem with channeling.
However, if you see very light, almost transparent water flowing out at the beginning of the extraction, you can be sure that unwanted channels have formed in the coffee cake. The water hasn't extracted the coffee properly, but has simply flowed past it. It can also happen that a crack in the coffee cake only breaks during the extraction. In such a case, water bubbles out of the spouts in the middle of the extraction, interrupting the smooth flow. With espresso machines like the Decent or Maro , a faster water flow is visible in the graph.
Bottomless portafilter?
However, channeling is best detected with a bottomless portafilter. By looking at the underside of the filter, you can see whether all the coffee is being extracted evenly and runs down smoothly, or whether there are isolated spots where the water is practically spurting out.
Ideally, the espresso from the bottomless portafilter initially flows evenly from all the holes. Then, the espresso settles into a medium-sized stream in all shades of brown. This looks so good that the espresso must taste good, too.
Channeling occurs when thin splashes of water erupt from the stream, squirting like a water pistol, scattering around the cup and even landing on the back of the espresso machine. These splashes are often much more watery than the main espresso stream.
But be careful: a small splash to the side during extraction doesn't necessarily indicate severe channeling. Micro-cracks during extraction always occur. The most important thing 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 careful when looking for traces of channeling. Not every small hole in a coffee cake is a sign of channeling. The escape of CO2, for example, can also 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 run from the top to the bottom of the sieve, you can be sure that this channel has negatively influenced the flavor during extraction.
How can I avoid channeling?
Whether you're preparing espresso in a restaurant or at home, we'll show you some classic mistakes that encourage channeling. If you avoid these mistakes, you'll significantly reduce the risk of channeling!
Mistake 1: Tamping without spreading
The coffee grounds aren't flowing evenly from the grinder to the portafilter. There's always a spot in the portafilter where a small mound of coffee grounds forms during grinding. If you now remove the portafilter from the grinder and compact the coffee grounds with the tamper, there will be spots in the coffee cake where there's significantly more coffee grounds than in others. The coffee cake may appear smooth and even at first glance, but the water will force its way through the spots where there's less coffee grounds, as there's less resistance there.
Therefore, it's absolutely essential to distribute the coffee grounds after grinding. You can, for example, gently tap the portafilter on the countertop to allow the grounds to settle. You can also gently tap the portafilter sideways with karate moves. A good WDT tool with a good distribution technique is a good tool for closing underground holes.
Mistake 2: Ignoring the peculiarity of the mill
Depending on the type of espresso grinder you use, different practices for puck preparation and distribution are required. Some cheaper grinders, in particular, tend to clump the coffee heavily at finer grinds. Others tend to pile the ground coffee more heavily on one side. When distributing the grounds, you should consciously work against this phenomenon.
Lumps are a persistent phenomenon that can almost only be broken up with a WDT tool. Where lumps aren't loosened but instead pressed down, they almost always create a predetermined breaking point for the brewing water.
Mistake 3: Knocking the portafilter with the tamper
Some courses or online tutorials recommend tapping the portafilter again after tamping. The idea is that particles that have become trapped on the edge of the portafilter due to static electricity will be pushed onto the coffee puck. Don't do this under any circumstances! The vibration will break up the already prepared coffee cake and create channels, especially at the edge of the portafilter, through which the water will shoot.
Mistake 4: Too much speed when clamping
Even if it looks cool, please handle the portafilter with care when clamping it in place. Don't hammer it into the brewing group—after all, you're not reloading a gun! Banging the portafilter against the brewing group will have the same effect as tapping it with a tamper. The coffee cake will break up, creating channels that can ruin your espresso. Instead, take an extra two seconds to clamp it in gently and enjoy a perfect extraction!
Mistake 5: Sloppy work
Working cleanly is one of the most important aspects of espresso making. You should always rinse the portafilter thoroughly, both to preheat it and to remove any old coffee grounds. Afterward, you need to clean the portafilter. Use our Barista Cloths , for example, for this. Due to the hydrophobic properties of coffee grounds, a damp portafilter can promote channeling.
Mistake 6: Using unsuitable dosing cups
Those who prefer single-dosing grinders 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 poorly designed dosing cups, causes significantly more channeling than grinding directly into the portafilter.
Poorly made dosing cups sink completely into the portafilter, leaving a crater at the edge that can't be filled back to the bottom of the portafilter, even with the best WDT technology. Some dosing cups are particularly prone to static buildup. Others have hard edges at the bottom where the sides of the cup meet the grounds. This shape then leaves an imprint, like a pound cake mold, in the grounds when they are placed into the portafilter.
This is one reason why our KM dosing cup has a rounded base 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 are suitable for the Delonghi Dedica, for example, as well as for 58mm portafilters.
Other factors that favor channeling
When grinding coffee, the coffee particles become electrostatically charged. As a result, the coffee grounds don't fall evenly into your portafilter, but often form small clumps. These clumps vary in size depending on the grinder. These clumps can make it difficult to tamp evenly. If your grinder produces such large clumps, you can try tapping the portafilter on a tabletop or using a WDT tool to break up the clumps to create a homogeneous ground coffee.
The problem with many espresso gadgets, however, is that they need to be used correctly and adjusted properly. If a leveling tool is incorrectly adjusted or you dig too hard into the coffee grounds with the WDT tool, you may end up creating the very channels you were trying to avoid.
This is how WDT works
The Weiss Distribution Technique (WDT) was developed by John Weiss to break up coffee lumps in the portafilter and ensure even distribution before tamping. This technique involves gently stirring the ground coffee with thin needles (0.3–0.5 mm) to prevent channeling and achieve better extraction. Ideally, the movement is slow and even, without over-disturbing the coffee bed. WDT can be combined with the Ross Droplet Technique (RDT) to reduce static buildup during grinding. A leveling tool can be used after WDT to even out the surface and further optimize extraction.
In our view, a leveling tool is more of a visual tool. We've listed the most important steps for preventing channeling above.
Conclusion: The most important thing about espresso is the barista
It's very difficult to avoid channeling 100 percent of the time. And as we already told you in the introduction, espresso can taste delicious even with a little channeling.
Furthermore, there's no need for expensive WDT tools, levelers, or even a minute-long puck preparation routine. Far more important than these things is you, as a confident barista.
Choose a good, solid grinder. When filling the portafilter, make sure the ground coffee settles well and doesn't form mounds. Tamp straight and don't let the portafilter zip into the brewing group faster than Lucky Luke can draw his Colt.
All of these tips are easy to integrate into your workflow, take only a few seconds, and are completely free! Because the most important thing when brewing espresso is you, the barista!
