How to determine the thickness of ground beans?

When grinding beans, the size of the powder depends on the way it is cooked. Generally speaking, the shorter the cooking time, the finer the ground powder; the longer the cooking time, the thicker the ground powder. In terms of actual cooking, the Espresso machine takes a very short time to make coffee, so the grinding is the finest, and the coffee powder is as fine as flour; it takes more than a minute to cook coffee in the "plug air" way, and the coffee powder is medium-sized grinding; American filter coffee takes a long time to make, so the coffee powder is the thickest, one by one like Beijing grains on a shell beach. Grinding coffee powder with the right thickness is very important for making a good cup of coffee, because the extraction of water-soluble substances in coffee powder has its ideal time, if the powder is very fine and cooked for a long time, resulting in excessive extraction, the coffee may be very bitter and lose its aroma. On the other hand, if the powder is coarse and cooked too fast, resulting in insufficient extraction, the coffee will be tasteless because it is too late to dissolve the water-soluble substance in the powder.