Why grind coffee last before extraction?

The barista's decision on the grind size, water temperature, and powdered water pen used for a bean basically determines the flavor of the coffee in the cup, not the impact that the brewing itself has on the coffee.
　　The impact of the grind on the extraction is huge, which is why some grinders sell for two or three hundred dollars, while others can sell for twenty or thirty thousand dollars, showing the subtle differences in the details of the flavor.
　　Home bean grinders basically choose small grinding discs, such as small Fuji, small Pegasus, small Pegasus, such as this kind of grinder, while commercial bean grinders usually choose the grinding disc will be bigger, like EK43, Ditting804, and so on.
　　We can compare the size of the disc on the flavor of the impact, I believe that many practitioners are impressed, in the case of insufficient financial budget, would rather buy a cheap large disc grinder, not willing to buy expensive brands of small disc grinder, the main reason is actually in the small disc grinder due to the small disc, the number of times of repetitive grinding, the disc is more likely to heat up, and therefore resulting in a high rate of fine powder.
　　We use a small grinding machine is very easy to appear when the grinding of coffee powder, the last drop a lot of fine powder down, these are because the grinding disk is too small repeated grinding caused by the results. The larger grinders do not have this problem, so the aroma is more likely to stay in the coffee cup.
　　A professional barista, in the coffee brewing process, will have their own very skillful set of processes, boil water, warm pot, wash filter paper ...... to all the things are ready, you will find that every barista to grind coffee beans to the last step to operate.
　　This is because the coffee beans after roasting, the cell walls will become hard and brittle, and we after grinding, is to make coffee similar to granulated sugar-like particles and then start extraction, but unlike raw beans, after roasting the coffee beans only need to apply a little force can be easily crushed.
　　After the coffee beans have been ground, we can observe through a microscope that the sticky part of the cell wall gap will be exposed on the surface of the ground coffee powder, and this sticky part is a mixture of coffee's soluble aromatic substances and oils. During extraction, these soluble aromatic substances will come into contact with hot water, so that the aroma and oils of the coffee are fully dissolved, which constitutes the flavor and taste of the coffee.
　　While coffee beans are easier to extract after grinding, it will also make the aroma disperse or speed up the oxidation of coffee powder, which will oxidize dozens of cups faster than coffee beans after being ground into powder.
　　Therefore, among the many "coffee extraction tips", it is important to start grinding before extraction as much as possible to retain the aroma better.
　　The choice of grinding particle size of the grinder is the most important step affecting coffee extraction, so the choice of grinder will also affect the overall taste and flavor of the coffee towards the grinder, in addition to electric or hand-cranked grinding points, different grinding discs also have different grinding structure, but from a microscopic point of view, even if the same scissors will be the same coffee beans cut into the general, the incision is not able to show the same incision state.
　　This is because the hardness of each part of the cell wall of the coffee bean itself is different, and during roasting, due to the caramelization reaction, the coffee bean hardens and expands, making the cell wall, which has different hardnesses, create even bigger gaps, so as long as there is a certain amount of force, the coffee bean will be broken from the most fragile place, which makes the coffee bean, after grinding, have an irregular shape. This is especially noticeable in coarse grinding.
　　This is why the different blades on the market, such as flat blades, conical blades, and ghost tooth blades ...... are all designed to grind the coffee beans more uniformly, thus realizing an even extraction.
　　A good cup of coffee is determined by many parameters and data to determine the flavor, and grinding is only one of the very important links!