What does the coffee channel effect mean? What is the impact of the espresso channel?

I recall that when I was learning espresso, I was tortured by the "channel". A lucky E person, really every time the extraction of coffee appears in the channel, the old master will suddenly appear behind you, a cold sound into the ear, "you ~ pierced ~".

What is this channel effect? If we use bottomless handle to extract espresso, the normal state of extracted coffee liquid is that the flow rate is uniform, and the coffee liquid gathers from the surrounding to the center and flows out in a column.

The most obvious feature of the channel effect is that it will produce a spray, that is, it will intermittently spit out small coffee liquid, or several coffee columns can not be gathered together for a long time, and in more serious cases, the flow rate of coffee liquid will be unstable, suddenly fast and then slow.

Why is there a channel effect? It turns out that water is inert and always chooses the easy way to go. In our process of extracting espresso, the pressed powder is like a wall that prevents water from passing through. When the density of the coffee pressed powder is the same, the water can not find a loophole breakthrough, but can only be "hard", then the water can only work together and slowly infiltrate the coffee pressed powder, so that the extracted coffee will be very rich, not a drop of water will sneak out. But if the density of this piece of coffee pressed powder is inconsistent, some parts are very loose, so that the water can easily break through this part to form a small channel, and the subsequent water can be "lazy" to drill into the hole. And then there's the coffee spray we've observed. This lazy water does not honestly extract coffee, so espresso will appear thin and sour. Maybe we can find ways to prevent from some problems that will lead to the channel effect. 1. Cloth powder problem. We know that the function of cloth powder is to distribute the coffee powder evenly and avoid the emergence of channels, but it often backfires. Now many baristas rely on cloth dispensers to assist with cloth powder. In fact, the one-word, three-leaf and four-leaf powder dispenser does not play a significant role in the overall uniform distribution of coffee powder, on the contrary, because extrusion will make a greater difference in powder density between the upper layer and the lower layer. If you insist on choosing this kind of powder dispenser, there is also a solution, that is to increase the amount of powder.

2. Coffee powder agglomerates. More static electricity, rich coffee bean oil and heavy moisture may cause coffee powder to agglomerate. And coffee caking is easy to make the density of the whole coffee pressed powder inconsistent, it is easy to produce channels. The solution is also simple: you can break up the agglomerated powder with a toothpick, or you can use a needle dispenser. 3. The problem of pressing powder. The powder layer after the cloth powder is still relatively fluffy, and the pressing powder is to turn the fluffy powder layer into a wall that blocks the passage of water. The direction of pressing powder should be vertically downward, and it should be "set the tone with one shot, do not hesitate". In front of the street, many friends are always hesitant when pressing powder, as if one side is crooked, so the other side makes the force press and becomes the other half crooked, repeated 3-4 times, so it is easy to produce channel effect.

4. The distribution of effluent of boiling head. Before extraction, you can open the boiling head and observe the distribution of water flow. under normal circumstances, the water coming out of the cooking head will have 5-6 water columns evenly distributed. If the water column is concentrated in one strip, the extraction of espresso will easily concentrate on the pressed powder and cause perforation (channel).

If the cooking head shows a water column, then the powder water net may be blocked by fine powder residue, and it is necessary to backwash or disassemble the powder water net for cleaning.