As air flows through the NutriMill, the filter keeps flour inside the canister where it belongs, for virtually dust-free milling. For best results, do not wash the filter, because flour water = glue! After each milling session, remove the filter and simply tap out the flour it has collected. Brush away any excess flour from the bowl with a pastry brush, then replace the filter. When you keep the filter dry, it should last for several years. Replacement filter for the NutriMill Plus grain mill only. This filter is NOT compatible with the NutriMill Classic or NutriMill Harvest mills.