were introduced to the market.The coffee filter rings were designed for use in percolators, and each ring contained a pre-measured amount of coffee grounds that were sealed in a self-contained paper filter.The sealed rings resembled the shape of a doughnut, and the small hole in the middle of the ring enabled the coffee filter ring to be placed in the metal percolator basket around the protruding convection tube.

Prior to the introduction of pre-measured self-contained ground coffee filter rings, fresh coffee grounds