Q: What causes the froth on espresso?A:...

Q: What causes the froth on espresso?

A: The brownish froth on espresso is sugar that has been caramelized by the heat and pressure inside the espresso machine. The caramel becomes aerated as it is expelled from the machine, making it frothy. Too low a pressure or temperature inside the machine, or a dirty pot, will prevent the sugar from caramelizing.