What is the effect of grindability on the taste of hand-brewed coffee? What is the appropriate thickness of coffee powder for making coffee?

Some friends complained to the front street that they often couldn't find the grinding degree of the coffee, and the coffee was either too sour or too bitter. Coffee grinding degree of this knowledge point because the variable is too large, for beginners, in most cases lies in the state of blind people touching the elephant. So Qianjie intends to combine the extraction time to help you understand the degree of grinding.

For the first time, coffee will become bitter when it is ground fine, and its taste will become lighter when it is roughened, which I believe we all know. But why is it that when it is ground fine, it will be bitter, and when it is roughened, the taste will become lighter? There are actually two reasons. The first layer is that the total surface area of the finely ground coffee powder is relatively large, and the distance between the surface and the interior of the coffee powder is relatively short, so the water is more permeated into the coffee powder to extract coffee substances. The total surface area of coarse ground coffee powder is relatively small, and the distance from the surface to the interior is relatively long, so the extraction efficiency is relatively weak because it takes a relatively long time for water to fully infiltrate into the surface. (of course, there are exceptions, that is, when coffee powder is ground to the thickness of flour, it is easy to lump and stick together. In this way, the extraction efficiency of caked coffee powder is relatively low. )

The second layer is that in drip coffee, coffee powder has another "identity", which is to block the rapid passage of water. In fact, we often talk about pressurized extraction Italian coffee machine, in fact, strictly speaking, it should be pressure filter type, the same water through the coffee powder layer through the filter pores of the powder bowl to extract coffee liquid. Friends who have read the article in Qianjie should be very familiar with it. Qianjie is first of all based on time when teaching you to adjust the degree of grinding. The reason is that when the coffee powder is rougher, the gap between the coffee powder will be larger, and the effect of blocking the flow of water is relatively weak, so the time consumed is relatively short. When the coffee powder is ground finer, the gap between the coffee powder is relatively small, the water is not easy to pass through, and the consumption time is longer.

When we go back to making coffee by hand, the same is true. When the coffee is ground finely, first of all, it is easy to be infiltrated into the internal extract by water, and then the effect of blocking the passage of water is strong. If you do not go underwater, you will soak the coffee powder for a long time, then the coffee made out is prone to bitterness. When the coffee powder is ground thicker, it takes a long time for the water to fully penetrate the coffee powder, at the same time, the gap between the coffee particles is large, and the water is relatively easy to pass through, so part of the water will flow through the powder layer without fully extracting the coffee material, resulting in the reason that the coffee is thin and tasteless.

So the appropriate hand grinding degree can also be verified by the time, which is a variable that we can't directly control. Qianjie to give an example for everyone to understand: when verifying the relationship between grinding degree and time, other parameters should be fixed, such as our amount of cooking powder (15g), powder-water ratio (1:15), water injection technique (three-stage type) and filter cup (V60), because the change of these parameters will also affect the change of extraction time. In the degree of grinding recommended in Qianjie, lightly roasted coffee beans are calibrated with a sieve number 20 to 80%, which is what we often call hand-pulverized fine grinding. The extraction time is about 1 minute 50 seconds to 2 minutes 10 seconds. In other words, if you follow the parameters of Qianjie and do it with the same amount of powder, ratio of powder to water, method, and degree of grinding, the extraction time is theoretically the same as that of Qianjie, between 1 minute 50 seconds and 2 minutes 10 seconds. If there is a difference, then it is likely that the degree of grinding is wrong, because other parameters are easier to judge right or wrong, and the degree of grinding is more difficult. The friend said: "my grinding degree can not be wrong, I also use the No. 20 screen to calibrate, which is also 80%!" There are two reasons that may make you misjudge. The first is the way the screen is used.

Qianjie recommended calibration operation method is to use 10 grams of coffee beans (or a multiple of 10, easy to calculate, the more powder, the more accurate the data), choose a grinding scale, grind the coffee powder and put it into a sieve, and then shake horizontally. until the particles no longer fall obviously (usually shake for 3-5 minutes). Then weigh the weight of the fallen powder, and then divide by the total amount of powder to get the over-screening rate. For example, if the amount of powder through the screen is 5g, then the over-screening rate is 50%. If you want to reach the standard of 80%, you need to adjust to a finer degree of grinding. re-grind to measure the over-screening rate until 80%. The second reason is the limitation of No. 20 screen and the grinding quality of bean grinder. The aperture of the No. 20 sieve is 0.85mm, so it can only tell which coffee powder is larger than 0.85mm and which is less than 0.85mm. As for the finest coffee powder and the thickest coffee powder, it cannot tell. Grinding quality better bean grinder, powder diameter distribution is more concentrated, coarse powder and fine powder are less, then there will be no problem. However, if the grinding quality of the bean grinder is not very good, the diameter gap of the coffee powder is large, and there are many fine and coarse powders, then the problem of long extraction time will occur even if the sieve passes through 80%.

Therefore, the extraction time is also a reference to judge whether the coffee grinding degree is accurate or not. When brewing coffee, if the extraction time is longer and more time is exceeded, you can taste the coffee first. There is indeed a problem that needs to be improved. You can appropriately adjust the grinding degree, for example, to 75% of the screening rate. See if the coffee flavor has improved. When sharing the knowledge of making coffee, Qianjie often said that the data is dead, and you can never copy other people's data to restore other people's taste. But the reason is the same, only to understand the principles behind other people's use of these data, and then combined with their own reality, summed up suitable for their own data, in order to make a good coffee.

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