影響咖啡風味的「通道效應」 What causes the channeling effect?
手沖咖啡萃取過程產生「通道效應」，會讓咖啡萃取不均勻。導致這杯咖啡混合了萃取不足與過度萃取的風味或口感。
The process of pour over brewing coffee creates a “channeling effect” that can cause the uneven extraction. This results in a mix of under- and over-extracted flavors or textures in the coffee.
什麼是通道效應呢？
依據水會挑輕鬆的路走(阻力較小處)的物理特性，若讓咖啡粉中造成「通道」的產生，水會優先選擇這樣的通道流動，這將使靠近通道的咖啡被萃取得較多；其他部分流量過低或者根本不流水而造成萃取不足，產生咖啡萃取不均勻的問題，這就是所謂的「通道效應」。
What is the channeling effect? According to the physical characteristics of water taking an easy path (where the resistance is low), if a “channel” is created in the coffee powder, the water will preferentially choose such a channel to flow, which will make the coffee near the channel more extracted. The flow rate of other parts is too low or there is no water flow at all, resulting in insufficient extraction and uneven coffee extraction, which is the so-called “channeling effect.”
通道效應怎麼造成？
What causes the channeling effect?
1.佈粉不均勻或是過於緊實
The powder is uneven or too tight
佈粉是容易被很多人忽略的細節，卻也重要的影響著後續萃取成功與否。咖啡粉在倒入濾杯內時，將粉平均分佈成小山丘狀即可，不需要做拍平的動作，經過拍打容易讓粉與粉之間空隙變小而扎實，易阻斷後續悶蒸所需的水流濕潤空間，達不到同時浸潤咖啡粉的目標。
Pouring coffee powder is a detail that is easily overlooked by many people, but it also has an important impact on the success of subsequent extraction. When the coffee powder is poured into the filter cup, the powder can be evenly distributed into small hills. There is no need to make a flat action. After beating, it is easy to make the gap between the powder and the powder smaller and firmer, and it is easy to block the subsequent steaming. The required water flow to wet the space cannot achieve the goal of infiltrating the coffee powder at the same time.
2. 咖啡粉無均勻濕潤
Coffee powder is not evenly moist
a.乾的咖啡粉會比浸濕的咖啡粉更排斥水，這與水分子的相互結合有關，乾燥的咖啡粉具有較低的親水性，因此沖煮一開頭的悶蒸越成功，達到將咖啡粉完整浸潤，對於均勻萃取越理想。
Dry coffee powder will repel water more than soaked coffee powder, which is related to the mutual combination of water molecules. Dry coffee powder has lower hydrophilicity. Therefore, if blooming at the beginning of brewing is more successful, the coffee grounds are fully soaked, ideal for even extraction.
b.沖煮過程，繞圈柔和注水，幫助水流穩定且均勻的浸濕咖啡粉。
During the brewing process, gently pour water in a circle to help the water flow stably and evenly wet the coffee powder.
3.咖啡豆中排氣旺盛的二氧化碳，阻絕水與咖啡粉的接觸
The strong exhaust carbon dioxide in the coffee beans prevents the contact between water and coffee powder
豆子新鮮或是焙度越重的咖啡豆，二氧化碳排氣越旺盛，二氧化碳會阻絕咖啡粉與水的接觸，而造成萃取不均勻，因此透過悶蒸讓咖啡粉充分浸潤並透過均勻注水，讓氣體排出，有助於後續較能完整的溶解出咖啡的芳香物質。
The fresh beans or the heavier roasted coffee beans, the more vigorous the carbon dioxide exhaust, the carbon dioxide will block the contact between the coffee powder and the water, resulting in uneven extraction. Therefore, through blooming the coffee powder is fully infiltrated and water is poured evenly and gas is discharged, which helps to dissolve the aroma substances of coffee more completely in the follow-up.
4. 注水時注到了濾紙和咖啡的交界邊緣
The water is poured to the junction edge of the filter paper and the coffee
若注水注到了邊緣，注入的水會直接經過濾紙，並未經過咖啡粉就流到分享壺中。
If the water is poured to the edge, the water will directly pass through the filter paper and flow into the sharing pot without passing through the coffee grounds.
是不是發現，原來我們平時所作的沖煮細節，就是為了避免通道效應的產生。跟著我們一步步了解萃取的運作原理，越熟悉越有助於將咖啡沖煮帶進好球帶，有了穩固的基礎概念，再透過變因的調整，找出心目中對味的咖啡。
Did you find that the brewing details we usually do are to avoid the channelinf effect? Follow us to understand the working principle of extraction step by step. The more familiar you are, the better it will help you to brew good coffee. With a solid basic concept, you can brew the coffee with the right taste by adjusting the factors.
│延伸閱讀：手沖咖啡黃金比例
│Futher reading：Perfect Pour-Over Coffee Golden Ratio
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