Fresh roasted coffee beans let off carbon dioxide in a "de-gassing" process. To keep beans fresh for as long as possible, they must be stored in a container which allows this carbon dioxide to escape as necessary, without allowing oxygen to get at the beans and cause them to go stale. MasonTops created Coffee Caps to transform any wide mouth mason jar into the ideal coffee bean storage vault. With Coffee Caps, you can keep beans fresh with jars you already have around the house. Just screw the Coffee Cap into place with any standard screw band (not included) and store your beans in a dark spot, like a cupboard.