What is Channeling Effect? How to Determine if Espresso is Over-Extracted?
A good espresso is the foundation of all espresso-based coffee drinks. Espresso can amplify the various strengths of coffee beans, while poorly made espresso will inevitably magnify their flaws. Therefore, learning how to properly craft a shot of espresso has become an essential path for baristas and coffee enthusiasts alike.
FrontStreet Coffee frequently mentions the term "channeling effect" in our articles because its occurrence during coffee extraction can negatively impact the taste of the coffee. Moreover, its frequency of occurrence is quite significant! So today, FrontStreet Coffee will share with you what exactly this channeling effect is and how to prevent it from happening.
What is the Channeling Effect?
The channeling effect in coffee refers to the uneven distribution of hot water during the extraction process. To obtain a delicious cup of coffee, besides ensuring stable parameters, we need hot water to evenly penetrate most of the coffee grounds so they can release an appropriate amount of flavor compounds.
In an ideal scenario, water would be influenced by gravity and actively seep downward, allowing coffee grounds to receive uniform extraction. However, water, being inherently lazy, will prioritize finding paths of least resistance and concentrate its flow through these easier channels.
What does this mean? Imagine watering a dry patch of land that has cracks in it. The water you pour will concentrate and seep primarily through these cracks. Once you understand this principle, it becomes quite easy to comprehend when applied to hot water extracting coffee!
This leads to a situation where areas receiving concentrated water flow become over-extracted, dissolving undesirable compounds that shouldn't be extracted! Meanwhile, areas not receiving sufficient water flow become under-extracted, meaning they don't dissolve enough compounds. These under-saturated coffee liquids then affect the entire cup, resulting in deficiencies in concentration and flavor.
Espresso extraction is most affected by the channeling effect! This is because espresso extraction requires hot water to dissolve about two-thirds of the soluble compounds from a coffee puck in an extremely short time, making all extraction parameters highly efficient. If channeling occurs under these extreme conditions, its impact on the coffee's flavor becomes quite significant.
Although we cannot directly observe the flow patterns of hot water during extraction, this isn't problematic. The manifestations of channeling effects are quite apparent after they occur. Even before tasting the coffee, you can identify whether channeling has occurred through the following indicators.
1. Holes in the Coffee Puck
The cause of channeling is the uneven distribution of coffee grounds in the puck, leading to inconsistent water flow resistance in different areas. This causes hot water to concentrate and break through areas with weaker resistance. Therefore, when channeling occurs during extraction, we will notice numerous dense holes on the surface of the removed coffee puck—these are the "channels" created by hot water penetrating through! This phenomenon is what we call "perforation."
2. Splashing During Extraction
The use of a bottomless portafilter helps us observe this phenomenon more directly, as bottomless portafilters were invented specifically for this purpose. Therefore, if we use a bottomless portafilter for extraction, channeling during the process will likely cause splattering as the espresso is released, as shown in the image below.
How to Solve the Channeling Effect?
Since the main issue is uneven coffee ground distribution, we only need to optimize the distribution step. FrontStreet Coffee has detailed the key points to pay attention to during the distribution step in our article "The Importance of Proper Coffee Distribution," where you can click the blue text to jump to detailed explanations.
Finally, FrontStreet Coffee suggests that those wearing light-colored clothes should maintain a certain distance during bottomless portafilter extraction. Otherwise, the channeling effect won't just make your espresso taste "all mixed up" and confusing—
Important Notice :
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