Coffee beans contain certain carbohydrates and proteins that act as surfactants. Surfactants lower the surface tension of water. The same material that allows for the formation of the tiny bubbles in the crema on top of an espresso also lowers the surface tension in a way that encourages brewed coffee to penetrate into recesses that even water cannot reach. A buildup of coffee residue quickly acquires a taint reminiscent of rancid butter and smoke.
Cleaning-coffee equipment requires the application of a solvent that is designed specifically for coffee. Commercial filter coffee equipment benefits from a daily soak in water and coffee-cleaning soap, just as we recommended for cleaning espresso equipment in our Barista One course. Domestic filter coffee equipment may not need a daily application of cleaning soap, but once-a-week use will help remove tannins and oils that build up on the surfaces of the equipment.