In a drip filter machine the brewing process consists of three stages. Initially in the filling stage, hot water is poured on the dry coffee grounds and begins to fill the filter, but doesn’t leave. In the steady state stage the bed is saturated, water is still entering the filter, but also leaving at the same rate. Finally in the draining stage no more water enters the bed but still drains out. Only the steady state stage is considered in this study. grind size: "The really surprising thing to us is that there are really two processes by which coffee is extracted from grains. “Initially, the concentration of coffee in the bed is determined by the balance between a rapid extraction from the surfaces of coffee grains and the rate at which coffee is removed from the coffee bed by the extracting water. Later in the process, the extraction is dominated by slow diffusion of coffee from the kernels of larger grains, which was initially negligible.” It had previous...