Channeling in Espresso

What Causes Channeling in Espresso?

By Coffeenated Stories | 4 min read

Updated On: OCT 23 2023

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Channeling in espresso happens when water finds a path to travel more easily through only one spot of the coffee puck. That specific path will have a much lower water resistance than the rest of the puck.

A place in the puck with lower resistance has a greater flow rate throughout the brewing process. The coffee grounds in the area of greater flow rate are becoming more extracted than the rest of the coffee, contributing to an unbalanced taste of the espresso shot.

Ideally, we want the entire volume of the puck to see an even amount of water, lengthwise and depthwise, resulting in every coffee particle having the same amount of soluble material extracted.

Since channeling cause some areas to get more water flow and over-extract the coffee, other parts will get less water flow and under-extract the coffee, which will decrease our extraction rate in general.

When water passes through the channel, it will eventually take all the soluble materials from the coffee there. When nothing soluble is left there, the water that runs through it will dilute the espresso in the cup, causing our overall extraction to drop.

How to Spot Channeling in Espresso?

The best way to visually see channeling in brewing espresso is to use a bottomless portafilter. There are few warning signs to look for, and there are most convenient to spot them by looking at the underside of the basket.

The Underside of a Bottomless Portafilter
The Underside of a Bottomless Portafilter
Charles Sims by Unsplash - https://unsplash.com/photos/k-w7laFKa0g

Watching the first drops of espresso flow from the bottom of the basket is a great way to see how evenly water moves through and exits the puck. We should not look for a perfectly even occurrence of drops throughout the bottom of the basket, but if we note a clear preference of one area vs. another, we may have channeling happening.

After the first drops fall into the cup and streams are formed, the next thing to look for is gaps at the bottom of the basket. When all is good, we will not be able to see any of the holes in the metal floor of the basket. The lovely colors of the crema will cover the entire bottom of the basket.

Sign of Possible Channeling
Sign of Possible Channeling
Tyler Nix by Unsplash - https://unsplash.com/photos/Z5-KxulzaPo

The areas where channeling happens will get plenty of flow, and the areas surrounding it will not get enough water flow, resulting in spots on the basket where no espresso is dripping.

The last sign of channeling is also the most obvious when using a bottomless portafilter. Some types of channeling can cause tiny and short squirts of espresso through the bottom of the basket, making a mess. While this is a clear indication of channeling, it doesn't mean that it is very intense channeling formed inside the basket.

How to avoid Channeling in Espresso?

When trying to avoid channeling in espresso brewing, we need to consider our equipment and techniques. Namely, playing a role in channeling takes our:

  • Espresso Basket
  • Coffee grind size
  • The distribution of the coffee and tamping method

Espresso Basket

There are many kinds of espresso baskets today. And almost all of them look identical, especially those with similar shapes.

The most crucial difference between them is not apparent to the naked eye. That difference is in the holes at the bottom of the basket.

Under the microscope, the basket holes should be identical and perfectly circular. We want a basket with perfectly round holes because the coffee particles could get stuck if the edges of the holes are jagged and create a clog of coffee in the area.

It is not a problem if a few holes get clogged here and there, but if many holes get blocked in the same place, that will restrict the water flow, and under extraction will occur.

Often, the manufacturers of premium baskets, in the packaging of the basket, include an image of the holes taken under the microscope.

Coffee Grind Size

Making espresso with coffee that is too finely ground will result in channeling. When the pressure of 9 bars of water hits the puck, the finer the coffee grounds are, the more compressed the coffee puck will become.

Finely Ground Coffee
Finely Ground Coffee
KATY TOMEI by Unsplash - https://unsplash.com/photos/PX6t5jB5I7k

And in that case, the tiny coffee particles will become so densely packed together that the water flow may stop entirely, or the puck will split under pressure and create channels in the basket. So the grind size of the coffee should be considered when trying to avoid channeling in espresso brewing.

For the puck to hold its integrity and compactness through the brewing process, we can use preinfusion. Preinfusion is a technique that soaks the grounds with a small amount of water before brewing, making them swell and saturated, which will better hold the puck during the brewing process.

The distribution of the coffee and the tamping method

The distribution of the ground coffee inside the basket is essential in avoiding creating channels in brewing espresso.

Pouring ground coffee into the basket directly from the exit of the grinder, we'll end up with a mound of ground coffee either in the center or on the side of the basket.

mound of ground coffee
Mound of Ground Coffee
Nguyen Tong Hai Van by Unsplash - https://unsplash.com/photos/pkj935eY62A

Before we temp the coffee down, we need to distribute it evenly through the basket and break apart any grounded coffee that might lump together. There are various tools for that, but sometimes a simple wine cork with a few needles stuck may do the job.

ready to distribute and tamp
The Coffee Before Distribution and Tamping
Distributing the Coffee Inside the Basket
Distributing the Coffee Inside the Basket
Tamping the Ground Coffee
Tamping the Coffee Puck
Noora AlHammadi by Unsplash - https://unsplash.com/photos/WI6tU-VbdBE
Ryan Spaulding by Unsplash - https://unsplash.com/photos/uJ9F3H7pkac
Simon Takatomi by Unsplash - https://unsplash.com/photos/Ef9mVxPg-30

After we distribute the coffee in the basket, we'll proceed with tamping. To tamp the coffee, we need to hold the portafilter rested on a solid surface and press the coffee inside the basket evenly with a tamper. We must be careful not to push one side more than the other because that will make the water run through the coffee unevenly.