So you’ve upgraded to a bottomless portafilter, but instead of being rewarded with beautiful streams of Instagram-worthy espresso flowing from the bottom of your filter basket, you're now face-to-face with uncontrollable channeling, random spurting, and unbalanced shots. What gives?
A bottomless portafilter, as gorgeous as it may be, is primarily a diagnostic tool to help you learn how to improve your technique. If you're seeing channeling and spurting from your bottomless, this is the tool giving you feedback that you have extraction issues happening inside your filter basket, ultimately leading to not only a messy counter, but a poorly extracted shot as well.
What is channeling?
Water will follow the path of least resistance, and this is particularly true when water is under pressure (ie. during an extraction). If your coffee is unevenly ground, or improperly distributed and/or tamped, water will not flow uniformly through your grounds. If there are gaps or inconsistencies in your grounds, the high pressure water will flow faster through these areas, creating what's called "channeling."
Channeling inside of your grounds will typically lead to spurting, which is visible in the form of streams or jets of liquid spraying from the filter basket. After brewing, you might also be able spot holes or cracks in the spent coffee grounds, which can be a sign that channeling has occurred.
Not only is channeling messy, but it's also a sign that you're extracting your grounds unevenly. The areas of high flow (in the channels) will tend to be over extracted, while the rest of your grounds will tend to be under extracted. This leads to improper flavors and an unbalanced espresso in your cup.
How to stop bottomless portafilter channeling
In a perfect world, your coffee will be evenly extracted and the stream will align beautifully in the middle of your bottomless portafilter every time. Achieving this super smooth shot and deliciously balanced cup is not impossible, but it does require a bit of experimentation and technique. We recommend making one adjustment at a time, not overhauling your entire process. Adjusting too many variables at once can leave you spinning in circles. Take your time to discover what works and what doesn’t. And if you're complete new to espresso, make sure to check out our beginner's guide to dialing in your shots. Once you've familiarized yourself with the general process, dive deeper into fine tuning your technique with the tips below.
Fresh Beans, Grind Size and Puck Prep
First and foremost, always use fresh roasted, whole bean coffee. You might be surprised how much of a difference this can make. If possible, try aiming for coffee roasted within the past 30 days, or even sooner, and never use beans from the grocery store shelf (unless it's from a fresh, local source).
Weigh your dose. We suggest single dosing and weighing your beans before grinding, but whether you weigh before or after grinding, make sure you're using the same amount of coffee into your portafilter each time.
De-clump your grounds. Some grinders, particularly grinders that are built into the espresso machine, will leave behind clumps while grinding. These clumps, if left alone, can cause inconsistencies in the coffee puck once tamped. One simple method of de-clumping your grounds is to shake them in a dosing cup, like the ones found here.
Use a WDT Tool. This simple, yet effective tool uses thin wires to gently rake through the coffee bed, breaking up clumps, closing gaps, and evenly distributing the grounds before tamping. This can be used in conjunction with, or completely separate from, the dosing cup mentioned above. Make sure to drop a dosing funnel on top of your portafilter before raking your grounds, which will help stop grounds from overflowing during the process.
Use a distribution tool before tamping. A distribution tool will help level out the grounds, preparing them for tamping. Make sure you're only applying light pressure while distributing. Applying pressure should be reserved for the tamping process.
Perfect your tamping technique. Straight/level tamping is key. Even a small shift in the angle of your tamping can ruin your work. Apply firm, even pressure to create a level surface on the coffee bed. Using a tamper with a collar, such as the one found here, can help ensure that you're tamping perfectly level, every time.
Try using a puck screen. A puck screen is a simple, effective and affordable tool to help control the flow and distribution of water through the grounds. Placed on top of the grounds after tamping, puck screens are used to disrupt the high-pressure flow of water from the group head and spread it across the bed of coffee.
Try manual pre-infusion. Pre-infusion is the process of pre-soaking your coffee grounds under low pressure, which can help to expand the grounds in your basket and provide a more even extraction. Most machines (including Breville) will automatically pre-infuse before every shot, but the automatic pre-infusion is often not quite long enough to soak the entire bed of coffee. If you're using a Breville machine, you can manually pre-infuse each shot by simply pressing and holding the single or double shot button. The machine will continue to pre-infuse until you let go of the button. When using pre-infusion, we typically hold the pre-infusion for around 10 seconds (give or take), or until the bottom of the filter basket fills with coffee. This is something you can experiment to see what works best for you. Keep in mind that extended pre-infusion can often cause your shot to extract slightly quicker than it otherwise may have without pre-infusion, so you may need to account for this while dialing in your other variables, such as grind size and tamping pressure.
Additional troubleshooting and caveats
Make sure your filter basket is clean and clear. A clogged filter is a surefire way to disrupt the flow of water.
Clean your group head and shower screen. Shower screens can also become blocked and clogged if not cleaned regularly, which can cause an uneven flow of water into the grounds.
Pressure output from the group head / machine itself can be a contributing factor to channeling and spurting. Most commercial machines will apply around 9 bars of pressure during extraction, which tends to be the sweet spot. Most Breville machines, however, have a higher pressure output, pushing upwards of 14-15 bars. These machines were set up this way for a reason, but one caveat is that the higher pressure output tends to exploit inconsistencies in the prepared coffee grounds. This in mind, puck prep tends to be more crucial to avoid channeling and spurting with these machines.
Practice, practice, practice
If you’ve tried all these tricks but your bottomless portafilter is still channeling and spraying, keep at it! Crafting espresso is as much an art as it is a science. Take your time while experimenting with different techniques, and make sure not to change too many variables all at once.
Just remember, at the end of the day (or more likely the beginning of the day), what matters most is that you're enjoying what's in your cup. Honing a new craft is a journey. Enjoy the ride along the way, and #LoveEveryShot.