Thermal Crema

For millions of people, a morning espresso is a simple daily ritual, but inside the portafilter of the espresso machine, a chaotic and incredibly precise physics experiment is taking place. The defining characteristic of a perfect espresso-the rich, golden layer of foam known as "e;crema"e;-is not actually liquid at all. It is a highly unstable emulsion of carbon dioxide gas and coffee oils. Whe...