Dynamics of liquid infiltration into an espresso bed using time-resolved micro-computed tomography: Insights from experiment and modeling

In espresso brewing, soluble content is extracted from a bed of ground coffee beans by forcing hot water through the bed at high pressure. An important part of this process is the infiltration stage in which water permeates the initially dry bed. This process is investigated by a combination of x-ray tomography and fluid mechanical modeling. Tomography is used to track the infiltration front of the water via the contrast in density. The experimental data are compared with a one-dimensional unsaturated porous medium flow model, which divides the bed into wet and dry regions and incorporates the espresso pump dynamics. Good agreement is seen between the experimental data and the model predictions.