How to appreciate a perfect Italian coffee espresso common sense

Look at:

The standard amount of a perfect Single Espresso is to extract an ounce of coffee essence in 25 seconds.

Look at the appearance Crema:

A perfect Italian coffee espresso, the surface is always thick, brown red Krima crema, Krima crema is the protein, oil and other aromatic components extracted from the coffee under high pressure, is the essence of coffee concentrate.

Perfect espresso, perfect Krima crema must be at least as thick as 4mm, and can't be broken by blowing gently. In the case of correct operation, if it becomes yellowish, or even white, it means that the coffee has been put for too long, expired; floating on the surface of Krima crema can also judge the situation of espresso operation, if the color is a little yellowish, white, the amount of coffee is too fast, which indicates that the extraction pressure is too small, insufficient extraction, the need for finer grinding, tighter and more uniform filling pressure to increase the resistance of coffee cakes. If the color is too dark, the outflow is not coherent, or even drips out, which indicates that the extraction resistance is too high and the pressure is too high for the extraction transition, but for the whole cake, it is not enough extraction, which is caused by too fine powder, too tight powder and too much powder.

Smell:

The perfect espresso should have a pleasant aroma and should never have a charred taste. If there is a charred taste, it is a pity that what you drink is a cup of over-extracted espresso.

Product:

The perfect espresso should be thick, not simply bitter, but a combination of aroma or sour taste, which is mainly related to the variety and combination of coffee beans.