We present a theoretical model of the flow of an ideal espresso shot through a portafilter, accounting for its non-Newtonian behavior, time-dependent viscosity, and anisotropic puck property. The dynamics are described using the incompressible Navier-Stokes equation simplified under laminar and low-Reynolds number conditions, and Darcy's Law and the Brinkman equation for porous media, and its time-evolving viscosity modeled as a function of temperature and time. Anisotropy in the coffee puck is modeled via a permeability tensor, allowing directional variations in flow to be considered. We consider thermal energy relations through a heat equation with viscous dissipation, ensuring consistency with the first and second law of thermodynamics. We discuss analytical solutions for idealized isotropic pucks and numerical approaches for anisotropic cases, with a normalized flux variance introduced as a quantitative factor to measure uniformity. This framework suggests how anisotropy affect flow distribution and highlights methods for predicting channeling in espresso extraction.
Roy Kim (2026) studied this question.