What Is Crema?
One of the aspects that defined the coffee produced by Achille Gaggia's patented espresso machine design in 1938 was the thick crema produced by the pressure brewing process. Rich crema has since become a desirable aspect among modern espresso drinkers, but what exactly is crema? In truth, crema is a foam, created by suspended solids and CO2 and is a phenomenon that only occurs in espresso, which was originally dubbed caffÃ¨ crema (cream coffee).
Unlike brewing drip coffee, where gravity pulls hot water through ground coffee at regular atmospheric pressure, espresso is ideally brewed at 9 bars of pressure, the key factor which allows for crema to be produced. The high pressure environment inside of the portafilter allows for the water to become supersaturated with CO2. When the water exits the portafilter in the form of espresso, the CO2 forms into thousands of tiny bubbles which are coated by parts of the oil extracted from the coffee, thus becoming the foam the floats on top of your espresso, aka, the crema.