The technique of brewing coffee is about the technology of pressing coffee powder.

I thought it had been described in my early diary, but later I found that it seemed simple and clear. I was negligent.

Yes, it's easy to explain the problem. But I like the way this friend asks questions, because he mentioned in his email that many authoritative baristas suggested not to do so, but I don't know why.

Let me explain a little bit now that this is actually related to the problem of uniform extraction. But before I begin, I want you to refer to my previous diary about powder pressing. (http://www.douban.com/note/177204875/)

I never tire of mentioning extraction in the extraction article. One of the principles of extraction is that the extraction is uniform. What is extraction? The process by which water is mixed into water through powder, or powder, and water absorbs coffee soluble matter. What is uniform extraction? It is not difficult to understand that as far as possible, each particle of powder is given the same proportion of soluble matter.

If there is something wrong with the grinder, the particles vary greatly, which will lead to uneven extraction. We all know this better.

If we press the powder askew, the part with less powder is infiltrated by too much water, and the part with more powder is not permeated enough, this will also lead to uneven extraction. This is more intuitive for us to see.

As in the picture

In many coffee shops, there is such a phenomenon, that is, after pressing the powder, there is some powder on the inner wall of the edge, so you need to knock on it to shake it off. This is what we call percussion. Points will be deducted in WBC. I would like to explain to you in the picture:

The purpose of pressing powder is not only to make the powder and powder tight, but also to seal the coffee powder and the filter bowl. The aim is to let the water produce uniform resistance to the powder bowl, as shown below:

However, in order to shake down the loose powder on the inner wall, you will see that the seal is broken. You think, if the water is too powdered (I encourage you to think of this scene once you think of the extraction, it is very helpful for you to make coffee, because it is very vivid), the water is inert and will first pass through the edge of the filter bowl. And this channel is opened, commonly known as the channel effect (channeling).

To make matters worse, even if you add powder, the channel still exists as shown in the following two pictures:

I press the powder again.

This crack cannot be remedied.

This will happen if you use a pedestal-less handle.

Through the picture, I think everyone will be more intuitive. So people will ask, what about the powder on the inner wall? The only effective way is to choose a powder press of a more suitable size. Of course, it is impossible to guarantee that the inner wall is completely clean. But the cleanliness of the inner wall has little effect on coffee production, and the coffee machine will be cleaned every day after use, which is not a major problem. But the harm of channel effect is obvious.

That's all I said, I just made a latte from the espress that may have a channel effect. Enjoy:)