The technique used by Rome’s renowned Caffè Sant’Eustachio to produce an astoundingly thick, foamy head of crema atop its signature Gran Caffè is a closely guarded secret. Screens on each side of the Astoria espresso machines block the view of nosey cafenatics seeking a peek at any covert manoeuvres performed by the baristas. Author/blogger David Lebovitz suspects that a small amount of sodium bicarbonate (baking soda) is added to the water to agitate the foaming action as espressos are pulled. My contacts at illy in Trieste and the incomparable Caffè Terzi in Bologna agree that some form of foaming agent is used. If so, the powder is likely added out of view and the screens are merely props in a theatrical illusion.