Keeps Brew Head Clean - Protects the brew head from grounds being sucked up when Lever is lifted. Easy Rinse to Clean - Easily flushed out under the tap to remove any grounds from within. Perfect Addition to Espresso Brewing - Improve water distribution and channeling. Note: Given the thermal mass of the screen, it is recommended that it is placed in the portafilter and locked in just before turning on the preheat controller.