Foam on the surface of "Espresso"

Foam on the surface of "Espresso":

Foam: coffee fat (Cream Crema), also known as aromatic oil, exists in the reddish brown foam on the surface of coffee, uniform color, about 3 mm ~ 5 mm thick.

It consists of vegetable oils, proteins and sugars.

Coffee fat has the combination of emulsion and foam colloid.

If the emulsion is dark brown or even black, the coffee is overextracted.

If it is yellowish, it means that the coffee has not been fully extracted.

Function: lock incense, heat preservation, increase alcohol.

Lock incense: can lock the volatile chemical molecules of coffee aroma.)

Color: hazel, dark brown, reddish