When the surface of the coffee grounds is unevenly tamped during espresso preparation—whether due to inconsistent pressure, uneven distribution of grounds, or an unsteady hand—distinct pathways or narrow channels are naturally formed within the compressed coffee puck. These irregular channels act as shortcuts for water flow, allowing the hot, pressurized water (typically between 9 and 10 bars of pressure in espresso machines) to pass through certain areas of the coffee bed far more quickly than others during the extraction process.

As a result, water distribution becomes highly inconsistent: some portions of the coffee grounds are over-extracted, releasing bitter compounds and astringent flavors, while other sections remain under-extracted, leaving behind sour or underdeveloped notes. Visible splashes often occur as the turbulent water forces its way through these uneven pathways, and the overall extraction becomes unbalanced, with the final espresso shot lacking the smooth, well-rounded character that defines a quality brew. This common yet problematic phenomenon in espresso preparation is technically referred to as the "channel effect" by coffee professionals, and it remains one of the most frequent challenges faced by both novice home baristas and experienced café operators alike.

How to mitigate the problem?

Tamper better

To effectively minimize this brewing issue and achieve the consistent, balanced extraction that is essential for a perfect espresso shot. Baristas can focus on developing and refining their tamping techniques: using a calibrated tamper to apply consistent pressure (usually between 30 and 35 pounds), ensuring the tamper is held perfectly level to create an even surface, and taking the time to inspect the puck from multiple angles before brewing to identify any potential uneven areas. Additionally, pre-tamping distribution methods, such as gently shaking the portafilter to settle the grounds or using a distribution tool to level the surface, can significantly improve the uniformity of the coffee bed and reduce the likelihood of channeling before tamping even begins.

Use a puck screen

Alternatively, there are several practical and proven solutions available to baristas of all skill levels. One highly recommended approach is to use a specially designed puck screen—a thin, precisely engineered mesh disk typically made from food-grade stainless steel—that is placed directly on top of the tamped coffee grounds before locking the portafilter into the machine. This simple yet ingenious tool acts as a barrier that diffuses the initial force of the water jet, ensuring that pressure is distributed evenly across the entire surface of the coffee puck and preventing the formation of destructive channels. 

Pre-infusion

Pre-infusion function also serves as an effective technique for baristas to minimize and counteract the channeling effect that often occurs during espresso extraction. This preliminary wetting stage allows the coffee grounds to expand uniformly and create a more consistent surface before the full pressure extraction begins. By evenly saturating the coffee puck with a controlled amount of hot water at low pressure, the pre-infusion helps prevent uneven water distribution that could lead to channeling - where water finds paths of least resistance through the coffee bed. This method enables baristas to achieve better extraction quality, as it reduces the likelihood of both under-extracted and over-extracted areas in the final brew. Many professional espresso machines now incorporate adjustable pre-infusion settings, allowing skilled baristas to fine-tune this important preparation phase based on specific coffee characteristics and desired flavor profiles.

 
HiBREW is here for the beginners

HiBREW meticulously designs and thoughtfully provides its professional-grade 51mm portafilter system, which includes a complete set of premium accessories. This comprehensive system comes equipped with a high-performance, precision-engineered puck screen that ensures optimal water distribution during extraction. The carefully designed portafilter system is particularly well-suited for coffee beginners who are taking their first steps into the world of specialty coffee, offering them an accessible yet professional-level brewing experience. 

Additionally, many of HiBREW's  machines, such as the popular HiBREW H10A model, incorporate pre-infusion technology that allows both home baristas and coffee professionals to achieve cafe-quality results. These pre-infusion functions help gradually saturate the coffee grounds before full pressure extraction, resulting in more balanced and flavorful espresso shots that showcase the full potential of specialty coffee beans.

So if you are just starting out and feeling a bit overwhelmed by the world of Espresso coffee, don't worry - HiBREW is here to guide you every step of the way! Whether you're a complete beginner looking to learn the basics or someone who wants to improve their home brewing skills, our friendly team at HiBREW has all the expert advice, quality equipment recommendations, and helpful tips you need to make perfect espresso at home. We understand that getting into espresso can seem daunting at first, but with HiBREW by your side, you'll be pulling delicious shots like a pro in no time! Let us help you begin this exciting coffee journey today!