The best espresso is characterized by foam (crema) of a light brown color (with a reddish shade), with light stripes evenly distributed in the foam.

Espresso foam can be very dense, homogeneous, and steady, with very few bubbles. The foam should have neither big bubbles or white spots (allocation of fractions of heavy caffeine), and should not have ruptures in the surface of the foam through which the coffee underneath can be seen.

A gray shade means that more Robusta beans than recommended have been used. A white shade, on the other hand, signifies an insufficient extraction during the brewing (quantity of coffee ground less than 6 grams, coarse grinding, insufficient pressure in the device, a water temperature less than 88 C °, water pressure below 9 atmospheres, time of extraction less than 20 seconds)

Black tops in crema and white bubbles breaking the foam signify too much extraction during the brewing (The quantity of coffee being more than 12 grams, fine grinding, high pressure in the device, water temperature more than 92 Degrees Celsius, water pressure above 9 atmospheres, extraction time more than 28 seconds). If the extraction is either insufficient or excessive, you’ll end up with practically no crema, due to the use of blends with limited quantities of oils and high-molecular glucids, or old ground coffee. The same also holds true for crema that disappears quickly.