The glass rod has a rough surface where it fits into the top bowl. The force of the heated water rising into the upper bowl prevents the coffee in the upper bowl from falling into the lower bowl as long as the pot remains over heat. Once the brewing time is up and the pot is removed from the source of heat the lower bowl will begin to cool. This change in temp. creates the vacuum that draws the coffee down into the pot. As the brewed coffee is "pulled" down to the pot below the wet coffee grounds collect against the glass rod's rough surface and only the liquid coffee passes thru into the lower pot. If another type of filter is used, such as a frame with a cloth filter attached the process is essentially the same with the exception that the wet coffee grounds are instead filtered out of the finished brew by the cloth or wire mesh if used. This is a rather simplfied explanation of the process. That being said, the Cory Glass Rod is an ingenious invention. Some people don't care for them,but if you use a grind coffee that is med. rather than very fine these filters work very well.
Eddie[this post was last edited: 12/8/2015-22:58]
Eddie[this post was last edited: 12/8/2015-22:58]