When I toured Italy in 1989 and 1991 I was reminded by roasters and food critics that one sign of an expertly made espresso was long lasting, thick crema. And at the time in our shops, crema remained thick and persistent for 90 seconds or more.
Then when we stabilized brewing water temperature to within one degree F in 2001 I noticed that along with all the sweetness we had preserved into the cup, crema became a light, delicate chiffon that dissapated quickly in the cup. If you were quick, however, it had a lovely, silky mouth-feel. Years have passed since then and I have learned that the sweet extraction we can now produce has a fundamentally different quality, probably due to the presence of the sugars. I trust it is here to stay.
Foam is composed of what are called long-chain surfactant molecules. Persistent foam is present when the molecules remain in unbroken chains, trapping the gas in the liquid. (Perkowitz “Foam”) I telephoned food scientist Carl Staub when this phenomenon first occured, and he suggested that the presence of more sweetness in the espresso might be the reason for this breakdown occuring more quickly in the crema.
It is important to consider this in enjoying caffe espresso as a culinary art, for the full flavor and silky texture: you must enjoy it immeadiately. Two quick sips from the hand of the barista, at the bar. The first sip is bracing, all the sass with lighter body, in the final sip are the sugars, which invariably sink to the bottom of the cup.