To maintain the smooth surface of the Bottle Grinder Set, we recommend cleaning them gently in lukewarm water mixed with soap flakes, using a soft sponge. Avoid detergents that contain sulfur compounds, which can damage the grinders surface. This will clean the grinder and make the smooth surface reappear. Wipe off with a clean damp cloth and thoroughly dry off before refilling it with salt/pepper. Avoid placing bottle grinders in direct sunlight. To avoid screeching sound whilst grinding, make sure the grinder is properly dry before refilling.