How will bubbles appear when steaming hand-brewed coffee affect extraction? How does the channel effect occur? How to solve uneven extraction?

You should have seen it more or less. In the process of steaming, there will be a lot of bubbles in some place of the powder bed, just like a little goldfish or a little crab hiding at the bottom and constantly exhaling. Although it is a very healing picture, but for some players, the emergence of this phenomenon is not a good thing!

As we all know, "stuffy steaming" is a process by injecting a small amount of hot water into the coffee powder bed to exhaust and expand the coffee powder! The hamburger produced by steaming is the appearance supported by the expansion of coffee powder and carbon dioxide. Due to the lack of hot water and short contact with coffee powder, most of the carbon dioxide of coffee powder can only be discharged slowly, so our steaming time is often as long as 30 seconds! But this is limited to normal-sized coffee powder. If, at the bottom, there happen to be some very fine powder hugged into a ball, then they are as small as having "sensitive muscles" in general, ready to trigger! When exposed to hot water, it expands rapidly and releases large amounts of carbon dioxide from the body, even if they are moistened by hot water that has cooled down (it's actually coffee liquid). And because the carbon dioxide released is too large, so under the package of oil, it will form one small bubble after another! Then these bubbles will continue to rise to the surface and be seen by us: one, two, three, one after another. Subsequently, the space in which the supply bubble rises forms a channel. We can see such a deep hole on the surface of the powder bed after the bubble is broken.

Why is this kind of situation unpleasant? Because water is inert, it tends to choose places with larger gaps and easier flow. And when there is such a hole when steaming, then it is possible to appear: uneven extraction! Most of the hot water injected during steaming may flow out of this gap, because the gap is larger and the water has better space to flow. This will lead to other coffee powder not fully infiltrated by water exhaust is not sufficient, in the back of hot water injection, because of the different degree of steaming, resulting in different extraction efficiency! And this is the channel effect that we often talk about!

In addition to the fine powder, the uneven injection of water during steaming and the uneven distribution of coffee powder will lead to the generation of channels! There is a good saying that there may not be a channel in the bubbling place, but the place where bubbles are constantly bubbling will certainly form a channel. When the channel is formed, the exhaust of the powder bed will be different, which will lead to uneven extraction. So many friends do not want to see a lot of bubbles after steaming. However, for hand-brewed coffee, the impact of the channel is not very great. Because the extraction process of hand washing for a long time can slow down the extraction difference caused by the channel, and what we often say "the channel effect is serious" refers to the extraction of Italian coffee! Because the coffee machine needs to quickly extract the substances from the coffee powder in a short time, it will be affected by the channel effect because of its high extraction efficiency.

Of course, many friends are perfect people who strive for improvement, so in order to reduce the impact of channel effect on cooking, we can reduce the generation of channels from these aspects!

First, spray a small amount of water before grinding if it is due to too fine grinding or too much static electricity caused by dry weather. So, what we need to do is to eliminate static electricity and prevent fine powder from huddling! And this is very simple! You only need to spray a small amount of water before grinding the coffee beans to reduce the clumping phenomenon of fine powder during grinding.

But it should be noted that do not spray too much water to prevent the bean grinder cutter head from rusting because of the residual moisture, then the loss outweighs the gain!

2. To distribute coffee powder evenly before brewing. If it is caused by the uneven distribution of coffee powder, we can use cloth powder needles or other needles to break up the powder bed before brewing, so that coffee powder can be evenly distributed! In this way, we can reduce the formation of the channel!

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