Why do you want freshly ground coffee before brewing?

If the diameter of the coffee powder is doubled, the volume of a single particle is reduced by 1 × 8, and the surface area of the corresponding total coffee powder is doubled. After the coffee bean is ground into coffee powder, its surface area increases exponentially, and the area of contact with air increases hundreds of times.

Once the extremely important acidic and volatile fats in roasted coffee beans come into contact with the air, the chemistry will change and the taste will become worse. The esters and aldehydes in the aromatization table of coffee are the most volatile, and the volatilization will make the coffee taste worse.

Not only is the volatile loss of aromatic substances, the oxygen in the air will also oxidize the aromatic components, especially the fat, resulting in the flavor of F. B. Freshly ground coffee powder quickly absorbs moisture from the air, increases weight and reduces the effectiveness of extracting coffee ingredients, complicating matters under internal molecular pressure.

Therefore, coffee powder bought in the store for a long time can only be used as "mummy fragments" of coffee, because the flavor of coffee powder loses a lot. In order to make a good cup of coffee, you must not buy coffee powder conveniently. It is the best way to use it now.

In addition, even when roasting coffee beans, the aroma of coffee is very easy to give off. Coffee beans that are well preserved for more than a week or two after roasting are not fresh, so not only should they be ground freshly, but also choose freshly roasted coffee beans that are well preserved as far as possible.