Anyone who takes espresso preparation seriously will eventually have to come to terms with the concept of 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 channeling is a monster in the closet, just waiting to jump out 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 out to ruin our perfect espressos!
When it comes to channeling, we advocate for staying calm! In the last 50 years, before bottomless portafilters were used, no one worried about channeling. And yet, the vast majority of espresso shots tasted delicious and didn't offend anyone.
Since the Third Wave of Coffee and the increased interest in the origin and production of coffee, every aspect of preparation is analyzed and scrutinized more closely. Channeling in the coffee puck does negatively affect the taste of the coffee, but it can be extremely minimized with simple steps! In our blog, we show you why channeling affects the taste, how to detect it in your espresso, and which preparation mistakes you should avoid.
What happens during channeling from a physical perspective?
When brewing espresso, hot water is pushed through the coffee puck and portafilter at a pressure of about 9 bars. As you already know, the extraction time of the espresso is the deciding factor for its taste. The longer the water is in contact with the ground coffee, the more particles are extracted. If the coffee is extracted for too long, it becomes over-extracted, tastes bitter, and has an unpleasant mouthfeel. If the water runs through the puck 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 for the water. The 9 bars press on the coffee puck, and the puck resists the water's passage. The water wins this battle, and the espresso slowly and creamily flows out of the portafilter.
Water takes the path of least resistance. Especially when water is under pressure, it hisses out wherever a small hole appears or a boundary is too thin.
This is exactly the effect that occurs during channeling. If the coffee puck has a small crack in its surface during grinding, distribution, or tamping, or if a hidden hole is concealed within the puck, the pressurized water will take exactly that path during the shot. Instead of evenly extracting the entire coffee puck in 30 seconds, a portion of the brewing water shoots right through this fracture point into the cup.
Even though your grind size might be perfectly set, the coffee at that specific part of the puck will be incorrectly extracted. The areas around the fracture in the puck will be extracted much more intensely because all the water is flowing through there. The other areas of the puck will be 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, that could be a sign of channeling. Of course, there can be other reasons as well. First, we recommend watching our video on 20 typical espresso preparation mistakes. If you have avoided all sources of error and your espresso tastes undrinkable at irregular intervals, that is a clear sign that you are occasionally experiencing channeling.
Channeling is even easier to recognize if you look closely at the spout of your portafilter. If the espresso comes out in a dark color with a creamy consistency and distributes evenly into two espresso cups, then you certainly do not have a problem with channeling.
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 puck. The water did not extract the coffee properly, but simply bypassed it. It can also happen that a fracture in the coffee puck only opens during the extraction. In such a case, water bubbles out of the spouts in the middle of the extraction, and the even flow is interrupted. With espresso machines like the Decent or Maro, a faster water flow is then visible in the graph.
Bottomless portafilter?
However, the best way to detect channeling is with a bottomless portafilter. By looking at the underside of the filter basket, you can see if all the coffee is being extracted evenly and flowing down in a creamy stream, or if there are individual spots where water is literally spraying out.
Ideally, the espresso will flow evenly from all the holes in the filter basket. Then, the espresso joins into a single, medium-thick stream in all shades of brown. This looks so good that the espresso is bound to taste good too.
We recognize channeling when thin water sprays break out of the stream, shooting like a water pistol and landing all around the cup or even on the back wall of the espresso machine. These sprays are often much more watery than the main espresso flow.
But beware: a small spray to the side during the shot does not necessarily mean 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 said to be people who can even predict the future from coffee grounds. However, we have found that you should be very careful when hunting for signs of channeling. Not every small hole in the coffee puck is a sign of channeling. The escape of CO2, for example, can also create superficial holes. Such small, superficial holes do not negatively influence the taste and are completely normal.
However, if you see large holes in your coffee puck that stretch from the surface to the bottom of the filter, then you can be sure that this channel negatively influenced the flavor during extraction.
How can I avoid channeling?
Whether you are preparing espresso in a commercial setting or at home, we show you the classic mistakes that promote channeling below. If you avoid these mistakes, you will significantly reduce the risk of channeling!
Mistake 1: Tamping without distributing
Coffee grounds do not land evenly in the portafilter from the grinder. There is always a spot in the portafilter where a small mountain of coffee forms during grinding. If you then remove the portafilter from the grinder and compress the grounds with the tamper, there are spots in the coffee puck where there is much more coffee than in others. The coffee puck might look smooth and even at first glance, but under pressure, the water will shoot through the areas with less coffee because the resistance there is lower.
That is why it is absolutely necessary to distribute the grounds after grinding. You can, for example, carefully tap the portafilter on the countertop to help the grounds settle. You can also give the portafilter gentle, lateral taps with your hands. A good WDT tool with a good distribution technique is a great tool for closing up subsurface holes.
Mistake 2: Ignoring the grinder's quirks
Depending on what kind of espresso grinder you use, a different approach to puck preparation and distribution is necessary. Especially some cheaper grinders clump the coffee heavily at finer settings. Others have a tendency to pile the ground coffee more on one side, creating 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. Where clumps are not loosened but instead just pressed down, a weak point for the brewing water almost always forms.
Mistake 3: Tapping the portafilter with the tamper
In some courses or internet tutorials, you are advised to tap the portafilter again with the tamper after tamping. The idea behind this is that particles that have stuck to the edge of the portafilter due to static electricity will be knocked onto the coffee puck. Do not do this under any circumstances! Through these vibrations, you break up the already prepared coffee puck and create channels—especially at the edge of the portafilter—through which the water will shoot.
Mistake 4: Too much speed when locking in
Even if it looks cool: when you lock the portafilter into the group head, please treat it with care. Don't slam it into the group head jerkily—you aren't loading a revolver after all! If you bang the portafilter against the group head, it has the same effect as tapping with the tamper. The coffee puck breaks, and channels are created that can ruin your espresso experience. Take two seconds longer to lock it in gently and enjoy a perfect extraction!
Mistake 5: Working uncleanly
Working cleanly 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, to remove old coffee grounds. Afterward, you must wipe the portafilter out. For this, use our barista cloths, for example . Due to the hydrophobic properties of coffee grounds, a damp portafilter can promote channeling.
Mistake 6: Using unsuitable dosing cups
Anyone who likes working with single-dosing grinders grinds into a dosing cup first and then fills the coffee from there into the portafilter. It sounds trivial, but it is a step that—especially with poor-quality dosing cups—provokes significantly more channeling than grinding directly into the portafilter.
Bad dosing cups sink completely into the portafilter and leave a crater at the edge that cannot be closed back up to the bottom of the filter, even with the best WDT technique. There are also dosing cups that promote static charge particularly strongly. Others have hard edges at the bottom where the sidewalls meet the base. This shape then acts like a sandcastle mold, leaving an impression in the grounds when it is put into the portafilter.
This is a reason why our KM dosing cup is rounded at the bottom and sits on the portafilter with side wings, preventing it from sinking 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 become electrostatically charged. The coffee grounds therefore do not fall homogeneously into your portafilter but often form small clumps. These are more or less pronounced depending on the grinder. These clumps can make a homogeneous tamp difficult. If your grinder creates such large clumps, you can try to break them up to create a homogeneous bed of grounds by tapping the portafilter on the table or using a so-called WDT tool.
The problem with many espresso gadgets, however, is that they must be used correctly and adjusted well. If a leveling tool is set incorrectly or you stir too vigorously in the coffee bed with a WDT tool, it may be that you are creating exactly the channels you actually wanted to avoid.
How to WDT
The Weiss Distribution Technique (WDT) was developed by John Weiss to break up coffee clumps in the portafilter and ensure even distribution before tamping. The coffee grounds are 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 stirring up the coffee bed too much. 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 smooth the surface and further optimize extraction.
In our view, however, a leveling tool is more of a visual tool. We have listed the most important steps for preventing channeling above.
Conclusion: The most important part of the espresso is the barista
It is very difficult to avoid channeling 100 percent of the time. And as we told you in the introduction, espresso can taste delicious even with minor channeling.
Furthermore, you don't need expensive WDT tools, levelers, or a minute-long “puck preparation routine.” Much more important than these things is you, as a confident barista.
Choose a good, solid grinder. When filling the portafilter, ensure that the coffee grounds can settle well and do not form mountains. Tamp straight, and don't let the portafilter fly into the group head faster than Lucky Luke can draw his colt.
All 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!
