Espresso machine group heads can get clogged with spent coffee grinds. To prevent the buildup, baristas must flush hot water through the shower screen after removing the portafilter. Volumetric machines can be programmed to do automatic flushing with a single button press. This saves time and energy, since the heating of water can be costly. If your machine isn’t volumetric, aim for a manual flush time of less than 2 seconds.