In a coffee machine, the ground coffee beans are separated from the coffee solution by using a/an ______.
Ground coffee beans are mixed with hot water, and the molecules in the beans dissolve into solution. But the solid residue of grounds is still mixed in with the coffee. To remove it, we pour the coffee through a special piece of paper called a "coffee filter." The liquid and any dissolved molecules pass through the material of the paper, while the larger, solid particles are caught and stay inside the filter. In this way, the coffee is purified from the grounds.