Anyone who delves deeper into espresso preparation will inevitably have to deal with the concept of channeling. This refers to the formation of channels in the portafilter, which prevents even extraction and negatively affects the enjoyment of coffee.
In coffee forums and video tutorials, one might almost think that channeling is the evil monster from the closet, just waiting to creep 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 intent on ruining our perfect espressos!
We advocate for composure when it comes to channeling! In the last 50 years, when bottomless portafilters were not yet used, no one worried about channeling. And yet, most 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 has been more closely analyzed and scrutinized. Channeling in the coffee puck negatively affects the taste of the coffee, but it can be extremely minimized through simple steps! In our blog, we'll show you why channeling actually influences the taste, how to recognize channeling in your espresso, and what mistakes you should avoid when preparing espresso.
What happens during channeling from a physical perspective?
When brewing espresso, brewing water is forced through the coffee puck and portafilter at about 9 bar pressure. As you already know, the extraction time of the espresso decisively determines its taste. 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 is 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 presses on the coffee puck, and the coffee puck prevents the water from passing through. The water wins this battle, and the espresso slowly and creamily emerges from the portafilter.
Water seeks 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.
Exactly this effect happens with channeling. If the coffee puck has a small crack in its surface during grinding, distributing, and tamping, or if a hidden hole is concealed within the puck, the water under pressure will take precisely this path during extraction. Instead of evenly extracting the entire coffee puck in 30 seconds, a portion of the brewing water will shoot directly through this weak point into the cup.
Even if your grind size is perfectly set, the coffee at this point of the coffee puck will be incorrectly extracted. The areas around the break in the coffee puck will be very strongly extracted because all the water flows through them. The other areas of the coffee 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 could be other reasons too. First, we recommend watching our video on 20 typical mistakes in espresso preparation. If you've avoided all these potential errors and your espresso occasionally tastes undrinkable, that's a clear sign that you sometimes experience channeling.
You can recognize channeling even better if you look closely at the spout of your portafilter. If the espresso comes out directly in a dark color and creamy consistency and spreads evenly over two espresso cups, then you certainly have no problem with channeling.
However, if you see very light, almost transparent water running out at the beginning of the extraction, you can be sure that unwanted channels have formed in the coffee puck. The water has then not properly extracted the coffee, but has simply passed it by. It can also happen that a break in the coffee puck only opens up 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 flow of water 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, you can see whether the entire coffee is extracting evenly and flowing down creamily, or if there are individual spots where the water is practically squirting out.
Ideally, with a bottomless portafilter, the espresso first flows evenly from all the filter holes. Then, the espresso comes together in a central stream of various shades of brown. It looks so good that the espresso must taste good too.
We recognize channeling when thin splashes of water break out of the stream, and, as if sprayed with a water pistol, land scattered around the cup and even on the back wall of the espresso machine. These splashes are often much more watery than the main flow of the espresso.
But beware: a small splash to the side during extraction does not necessarily mean severe channeling. Micro-cracks during extraction always occur. The most important thing is always the result in the cup.
Is reading coffee grounds worthwhile?
There are indeed people who can even predict the future from coffee grounds. However, we have found that you should be very careful when searching for traces of channeling. Not every small hole in the coffee puck is a sign of channeling. For example, the escape of CO2 can also create superficial holes. Such small, superficial holes do not negatively affect the taste and are completely normal.
However, if you see large holes in your coffee puck that extend from the top to the bottom of the filter, you can be sure that this channel has negatively affected the taste during extraction.
How can I avoid channeling?
Whether you're making espresso in a gastronomic establishment or at home, we'll show you classic mistakes below that encourage channeling. If you avoid these mistakes, you'll significantly reduce the risk of channeling!
Error 1: Tamping without distributing
The coffee powder does not land evenly from the grinder into the portafilter. 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 coffee powder with the tamper, there are spots in the coffee puck where there is much more coffee powder than in others. The coffee puck may look smooth and even at first glance, but the water will shoot through the areas where there is less coffee powder under pressure, as the resistance there is lower.
Therefore, it is absolutely necessary to distribute the coffee powder after grinding. You can, for example, gently tap the portafilter on the countertop to settle the coffee powder. You can also nudge the portafilter with gentle, sideways karate moves. A good WDT tool with a good distribution technique is a good tool to close subsurface holes.
Error 2: Ignoring the grinder's quirks
Depending on the type of espresso grinder you use, a different approach to puck preparation and distribution is necessary. Especially some cheaper grinders clump the coffee together significantly at finer grind settings. Others tend to heap the ground coffee more on one side into 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 and are instead pressed together, a weak point for the brewing water almost always forms.
Error 3: Tapping the portafilter with the tamper
In some courses or internet tutorials, you are advised to tap the portafilter with the tamper again after tamping. The idea behind this is that particles that have adhered to the edge of the portafilter due to static electricity are pushed onto the coffee puck. Do not do this at all! The vibrations will break up the already prepared coffee puck and create channels, especially at the edge of the portafilter, through which the water will shoot.
Error 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 reloading 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. Take two more seconds for careful locking in and enjoy a perfect extraction!
Error 5: Untidy work
Cleanliness is one of the most important disciplines in espresso making. You should always rinse the portafilter well, partly to preheat it and partly to remove old coffee grounds. Afterwards, you need to wipe out the portafilter. For example, use our barista cloths . Due to the hydrophobic properties of coffee powder, a damp portafilter can promote channeling.
Error 6: Using unsuitable dosing cups
Those who like to work with single-dosing grinders first grind into a dosing cup and then transfer 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 direct grinding into the portafilter.
Poor dosing cups sink completely into the portafilter and leave a crater at the rim, which cannot be sealed back to the bottom of the sieve 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 base. This shape then forms an impression in the ground coffee, like a sand-cake mold, when it is inserted into the portafilter.
This is one reason 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 are suitable for the Delonghi Dedica, for example, and for 58mm portafilters.
Other factors that promote channeling
When grinding coffee, the coffee particles become electrostatically charged. This means the coffee powder doesn't fall homogeneously into your portafilter, but often forms small clumps. These vary in severity depending on the grinder. These clumps can make homogeneous tamping difficult in the portafilter. If your grinder produces such large clumps, you can try to break them up by tapping the portafilter on the table or using a so-called WDT tool to create a homogeneous coffee powder.
The problem with many espresso gadgets, however, is that they need to be used correctly and well-adjusted. If a leveler tool is incorrectly set or you stir too aggressively in the coffee grounds with a WDT tool, you might actually create the channels you were trying to avoid.
How to do 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. This involves gently stirring the coffee grounds with thin needles (0.3–0.5 mm) to avoid channeling and achieve better extraction. Ideally, the movement should be 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 even out the surface and further optimize extraction.
From our perspective, however, a leveling tool is more of an optical tool. We have listed the most important steps to prevent channeling above.
Conclusion: The most important thing about espresso is the barista
It is very difficult to always avoid channeling 100 percent. 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 are you, as a confident barista.
Choose a good and solid grinder. When filling the portafilter, make sure the coffee grounds settle well and don't form mounds. Tamp straight and don't let the portafilter snap into the brew group faster than Lucky Luke can draw his gun.
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 brewing espresso is you, the barista!
