Crema, noun: Thick, golden-brown froth that forms on top of correctly prepared espresso. Consists of coffee bean oil, proteins, sugars and carbon dioxide. More crema forms on Robusta espressos than on pure Arabicas. This is why blends are frequently made from both varieties. The beans need to be ground very finely so that crema can form. Inexpensive espresso machines, fully automated coffee machines and machines with pads produce an artificial crema with coffee frothed with air through a valve. You can recognize this through its coarse bubble structure. Test: Poor one teaspoon of granulated sugar on top of an espresso that hasn’t been stirred yet. It should remain on top for 3-5 seconds if the crema is real. Note that it does not form immediately after the espresso has been poured, but rather rises from the espresso a few seconds afterwards.