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What Is Espresso Channeling & How to Avoid it?

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Espresso channeling is when water doesn’t flow through your coffee grounds evenly. Resulting in espresso that tastes sour or bitter from under- or over-extraction. Keep reading to learn what causes it and how to prevent it.

As an espresso enthusiast, I’ll sometimes run into espresso channeling. That inspired me to write this guide on identifying and preventing it to help those who frequently experience it.

This guide will cover what it is, signs, causes, and prevention steps to take. Once you finish reading, you’ll have better-tasting, channeling-free espresso.

Here is an overview:

Let’s get to it.

Key Takeaways

  • Espresso channeling is the uneven flow of water through coffee grounds.
  • It can result in bitter- or sour-tasting espresso.
  • Uneven tamping & distribution could lead to channeling.
  • Prevent channeling with pre-infusion, better grounds distribution, & other methods.

What Is Espresso Channeling?

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What Is Espresso Channeling & How to Avoid it? 2

Espresso channeling is an uneven water flow through the coffee grounds during espresso extraction. This irregular flow can happen when there are weak spots in the coffee bed, such as air pockets or large particles.

The water will flow through these weak spots more easily, creating a wider and faster channel than the rest of the bed. This can lead to over-extraction and under-extraction in the rest of the bed. Resulting in a sour or bitter shot.

Over-extraction means you’ll have an Extraction Yield (EY) of more than 22%, which leads to a bitter shot. Under-extraction results from having EY under 18% and will result in sour shots [1]. The ideal Extraction Yield is between 18% and 22% [2].

Signs of Espresso Channeling

The following are signs of espresso channeling:

  • Hole in coffee puck: Remove the portafilter & inspect coffee puck, if you see holes, there’s uneven extraction.
  • Espresso firing from filter: Espresso will shoot at you from different parts of your filter where there’s more pressure.
  • Pouring espresso isn’t centered: Your coffee won’t pour from the center of your portafilter.
    • It could also pour from one or multiple sides of your portafilter.
  • Turning pale (blonding) too fast: Coffee that blonds too fast is a sign of under-extraction.
  • Donut extraction: Espresso pours from edges of your portafilter instead of center.

Get a bottomless portafilter to help you diagnose whether you have espresso channeling. Since it doesn’t have a bottom, you’ll have a visual indicator of what part of your espresso puck has more pressure. Such a visual will help you identify gaps.

Causes of Espresso Channeling

Here are the likely culprits of espresso channeling:

  • Too fine grinds.
  • Uneven grounds saturation.
  • Overfilling portafilter.
  • Side tamping
  • Bad coffee grounds distribution.

The following sections will explain many of the potential causes of espresso channeling. Use this information to help you understand what not to do when brewing espresso to prevent channeling.

1. Too Fine of Grind

Coffee grounds ground too fine can lead to espresso channeling because they create a more dense puck. This can make it difficult for the water to flow through the puck evenly, and can lead to the formation of channels.

Some suggest the ideal grind size for espresso is 0.3 millimeters [3]. Grounds finer than this may result in channeling.

2. Uneven Grounds Saturation

Uneven grounds saturation can lead to espresso channeling because it creates areas of the puck that resist water flow more. This can cause the water to flow through the puck unevenly, creating channels.

3. Overfilling the Portafilter

Overfilling the portafilter can lead to espresso channeling because it can create an uneven puck of coffee grounds. This can make it difficult for the water to flow through the puck evenly, leading to channel formation.

Overfilling your portafilter will also lead to a dry espresso puck, which results in under-extraction. Or sour-tasting coffee.

4. Side Tamping

Side tamping is the most common type of espresso channeling.

Side tamping is when you tamp the coffee grounds in the portafilter from one side only. This can lead to side channeling. An event when water flows through a small portion of the coffee grounds, resulting in a weak and uneven extraction.

When you tamp the coffee grounds from one side only, you create a high-pressure area on that side. This can cause the water to flow through that area more quickly. Meanwhile, the water on the other side of the puck has a harder time flowing.

To avoid side channeling, tamp the coffee grounds evenly. Do this by using a tamper that is the same size as your portafilter and by tamping the grounds in a circular motion.

You should also avoid applying too much pressure when tamping—over 30 lbs of pressure—as this can also lead to side channeling.

5. Bad Coffee Grounds Distribution

When the coffee grounds are not evenly distributed, some puck areas will have more dense(ness). These denser areas make it more difficult for water to flow through. The less-dense areas make it easier for water to flow through.

Effects of Espresso Channeling on Espresso Quality

Espresso channeling can have a significant impact on the quality of espresso. It can cause the espresso to be unevenly extracted, resulting in a sour or bitter taste. Channeling can also lead to a weak or watery shot.

How to Prevent Espresso Channeling

Here are ways to prevent channeling with your espresso:

  • Grind coffee beans evenly.
  • Use the right amount of coffee.
  • Pre-infusion.
  • Use a puck screen.
  • Distribute coffee grounds evenly.

The following sections will dive further into each prevention method. And they’ll provide more information on how they’ll prevent channeling.

1. Grind the Coffee Evenly

When filling your portafilter with coffee grinds from a grinder, move the portafilter in small circles when filling.

Also, avoid using blade grinders for espresso. These won’t provide consistent grinds, which may also lead to channeling. Use conical or flat burr grinders instead. The latter burr grinder will provide even more consistent grinds, but costs much more than the former.

2. Use the Correct Amount of Coffee

Use the amount of coffee that your manufacturer recommends. Lower doses will leave too much space at the head of your basket, which could decrease pressure and increase chances of channeling.

Using too less of coffee grounds will also lead to a soggy espresso puck, which will result in an over-extracted beverage.

Read through your espresso machine’s manual and see what the manufacturer recommends. If you lose the manual, you could likely find it online.

3. Pre-infuse Your Coffee

Uneven grounds saturation is part of what causes espresso channeling. In that scenario, we’d want to pre-infuse your coffee grounds to wet your coffee beans.

Pre-infusion is applying low pressure (2–5 bars) to coffee grounds before brewing. Some machines will automatically do this for you. While the rest require you to pre-infuse manually.

If your machine doesn’t include a pre-infusion feature, you’ll need a gauge to know how much pressure you’re applying.

Start by pre-infusing your beans for around 2 to 8 seconds. Depending on your preference, you could adjust for whatever amount of time.

Pressure manipulation, the process of using varying amounts of pressure, may also help. This involves pre-infusion and other amounts of pressure (e.g., 3, 6, 9, 6, and 3 bars).

4. Use a Puck Screen

A puck screen is a thin, perforated metal disc that sits on top of the coffee grounds in the portafilter. It helps to prevent channeling, which is when water flows through a small part of the coffee grounds, resulting in a weak and uneven extraction.

Here’s how a puck screen helps prevent channeling:

  • Holes in the puck screen help distribute the water over the coffee grounds, preventing it from flowing through a small portion of the puck.
  • Creates a barrier between the coffee grounds & the group head, preventing the coffee grounds from expanding.
  • Helps to prevent the coffee grounds from clogging the showerhead, which is the part of the group head that distributes the water.

Puck screens are a relatively inexpensive and easy way to improve the quality of your espresso. They are especially helpful if you are a beginner or if you are experiencing channeling problems.

5. Distribute Coffee Grounds Evenly

Here are a few ways to distribute coffee grounds more evenly:

  • Use tools (easiest): Get a coffee ground leveling tool to rake, de-clump, & distribute coffee grounds.
  • Tap method: Tap & knock portafilter against counter to remove air pockets.
  • Stockfleth method: Use index finger to distribute grounds & level them with basket rim.

I recommend using a WDT distribution tool. It acts like a rake to break down and distribute coffee grounds in your portafilter. It doesn’t cost too much and ensures you’re thorough with distributing coffee grounds.

Or use a paperclip to de-clump coffee grounds. Using this will take much longer than using a tool and may not properly de-clump your grounds.


Espresso channeling results from an area of your espresso puck having uneven pressure. Uneven distribution, too fine of grinds, or other factors could lead to it and result in over- or under-extracted coffee.

Explore our other guides to learn more about factors that’ll affect your espresso’s taste.

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Tim Lee is, as you might have guessed the founder of He is a former barista and a professional web publisher. He has now combined his knowledge and expertise in both subjects to create
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