The pestle and Ziploc bag method is a simple and effective way to grind coffee without a grinder. It involves using a Ziploc bag and a rolling pin or pestle to crush the beans into a fine powder. To use this method, place your coffee beans in a Ziploc bag and seal it, use a rolling pin or pestle to crush the beans until they are finely ground, and repeat the process until you have the desired amount.