Surprising! Even Pour-Over Coffee Can Experience Channeling Effects!

"Channel effect" refers to a phenomenon where water, due to its inertia, finds a shortcut during the extraction process and passes through it. Since this portion of water taking the shortcut doesn't contribute to complete extraction, it ultimately results in uneven extraction. Whenever FrontStreet Coffee mentions the channel effect, it's mostly in articles related to espresso coffee! But in fact, not just espresso, pour-over coffee extraction can also produce channel effects!

The reason why channel effects in pour-over extraction are almost always mentioned in the context of espresso is that when this effect occurs, it has a relatively large impact on the taste and flavor of espresso coffee, whereas the impact on pour-over coffee is not as significant. Additionally, due to the visualization of its extraction process, we can sometimes provide timely remedies when channel effects occur.

Why Channel Effects Occur in Pour-Over Brewing

Generally, drippers like V60 and Origami that use rib supports to hold up the filter paper and create water flow gaps are more prone to producing channel effects. Because these drippers are specifically designed with gaps to avoid over-extraction caused by prolonged soaking during brewing, the purpose is to allow water to pass through more quickly!

Therefore, when pouring water, not all hot water flows downward completely. Instead, while flowing downward, it also flows out from the gaps created by the surrounding rib supports, significantly speeding up the drainage! Generally, the periphery will be covered with coffee particles due to the impact of water, so when hot water passes through these gaps, it will first "carry away" the soluble substances hidden in the coffee powder wall!

How Channel Effects Affect Extraction

However, if the injected hot water doesn't hit the coffee powder wall, this portion of hot water will directly seep out from the gaps, playing no extraction role, and instead dripping directly into the server, affecting the coffee's extraction and taste - this is what we call the channel effect. A milder case occurs when too much hot water is injected, flooding over the powder bed! Since the amount of coffee powder is limited and won't completely cover the filter paper, when hot water floods over the powder wall boundary, this portion of hot water will directly escape through the top gaps without participating in any extraction!

But as we mentioned, this is a situation with relatively minor impact. Because only a small portion of hot water at the top layer is affected, other hot water within the powder bed still plays a good extraction role. If using multi-stage brewing, we only need to adjust the pouring method in subsequent brewing to avoid some negative sensations! Then there are situations that cannot be remedied: when we finish brewing, if you find a relatively large gap in some parts of the powder wall, allowing direct visibility of the filter paper, it indicates that due to improper brewing methods (continuous large circular movements, or fixed-point pouring at corners), channel effects occurred during the extraction process! Since this state is observed after extraction ends, it's almost impossible to remedy!

Severe Channel Effects and Their Consequences

But the above channels are still relatively mild in degree. For severe cases, you can see very abrupt fault lines!

This is caused by excessive impact force of the water stream during pouring, which collapses the powder wall. This type of situation is more serious, as large amounts of hot water that haven't undergone extraction directly drip into the server, with their only effect being to impact the final coffee taste! Thinness, astringency, and impurity are the most common manifestations of coffee with such powder walls!

Preventing Channel Effects

Of course, not all powder walls subjected to strong impact will show fault lines! For example, at the beginning, although the powder wall was subjected to greater impact force and produced fault lines, due to subsequent brewing causing the water level to rise, the coffee particles at the top will re-cover this broken powder wall as they descend, creating the illusion of normal extraction! Therefore, when we observe channel effects occurring during the extraction process, be sure to correct the brewing method next time: reduce large circular pouring to avoid hitting the cup edge, lower the pouring height to reduce water flow impact force, etc. These can effectively reduce the occurrence of channel effects~

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