What Causes Pour-Over Coffee Blockage and Poor Water Flow? Why Shouldn't You Tap the Dripper? How Do Fine Particles Cause Coffee Over-Extraction?

The Coffee Brewing Perfectionist's Dilemma

I believe some friends might share FrontStreet Coffee's tendency toward temporary "perfectionism" when brewing coffee! Whenever we spot irregularities during the process, we feel compelled to "fix" them into a neat, orderly appearance. For example, during the preparation before brewing coffee - wetting the filter paper! When the filter paper doesn't perfectly adhere to the dripper, we want to press down the protruding parts to make it fit completely against the dripper!

Or during the waiting time after the second pour of hot water, when we notice the gradually emerging coffee bed is uneven, we deliberately add more water to the area with more coffee grounds, hoping to create a more symmetrical coffee bed at the end. Additionally, when pouring coffee grounds and finding them distributed unevenly - more on the left side than the right - we might tap the dripper to level the grounds! We believe this allows hot water to extract all coffee grounds more evenly, resulting in more delicious coffee.

However, in reality, this approach may backfire because it can trigger probability events: clogging tends to occur during extraction, producing undesirable over-extracted flavors.

FrontStreet Coffee's Experiment

FrontStreet Coffee previously conducted an experiment: pouring two portions of coffee grounds from the same angle, then brewing one directly while tapping the other several times before brewing. The results were very clear - the untapped group completed extraction in 2 minutes, while the tapped group finished in 2 minutes and 21 seconds with a bitter taste due to clogging during the process.

Why Tapping Creates Problems

Why does leveling the coffee bed create such consequences? Because coffee grounds ground by a grinder are not absolutely uniform! Just like extraction, they can only make most particles similar, not all identical. Therefore, in a portion of coffee grounds, there are both large particles and fine ones. (Large and small particles separated from the same portion of coffee grounds)

When we tap the dripper, it creates vibrations throughout the entire coffee layer. These vibrations cause larger coffee particles to move to the upper layer while fine particles sink to the bottom - this phenomenon is what FrontStreet Coffee often refers to as the Brazil nut effect. When fine particles accumulate at the bottom, they more easily clog the filter paper, thereby extending extraction time and causing unexpected extraction results.

Additional Risks of Excessive Tapping

Furthermore, if tapping is done excessively, once fine particles reach the bottom, their smaller particle size reduces the gaps between coffee particles! With multiple taps, these gaps become increasingly smaller, making it more difficult for hot water to pass through! We can clearly see the consequences of this during the bloom phase: a small amount of hot water cannot quickly penetrate the coffee layer and flows along the edges due to inertia, making uneven extraction more likely to occur!

Proper Coffee Ground Distribution Techniques

Therefore, FrontStreet Coffee suggests everyone pay attention to how they pour coffee grounds - aim for the center point of the dripper and pour slowly to reduce uneven distribution of coffee grounds. This way, you won't need to bear the risks caused by tapping! However, if you're not careful and the grounds distribution still appears uneven, don't worry. We only need to pick up the dripper and gently shake it to achieve relative evenness! The number of shakes should not be excessive, otherwise the same problems will occur. (The image below is exaggerated - please do not imitate)

Alternative Solutions

Tapping is not entirely unacceptable, but the force and frequency need to be properly controlled to avoid the Brazil nut effect! Using a distribution tool can also be an excellent choice - not only can it help level the coffee bed, but it can also break up clumped fine particles, giving hot water more flow space and making extraction more uniform~

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473