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Coffee extraction involves many complex physical and transport processesextremely difficult to model. Among the many factors that will affect the finalquality of coffee, the microstructure of the coffee matrix is one of the mostcritical ones. In this article, we use X-ray micro-computed (microCT) techniqueto capture the microscopic details of coffee matrices at particle-level andperform fluid dynamics simulation based on the smoothed particle hydrodynamicsmethod (SPH) with the 3D reconstructured data. Information like flowpermeability and tortuosity of the matrices can be therefore obtained from oursimulation. We found that inertial effects can be quite significant at thenormal pressure gradient conditions typical for espresso brewing, and canprovide an explanation for the inconsistency of permeability measurements seenin the literature. Several types of coffee powder are further examined,revealing their distinct microscopic details and resulting flow features. Bycomparing the microCT images of pre- and post-extraction coffee matrices, it isfound that a decreasing porosity profile (from the bottom-outlet to thetop-inlet) always develops after extraction. This counterintuitive phenomenoncan be explained using a pressure-dependent erosion model proposed in our priorwork. Our results show that microCT scan can provide useful microscopic detailsfor coffee extraction modelling and establish the basis for a data-drivennumerical framework to explore the link between coffee powder microstructureand extraction dynamics. The latter is the prerequisite to study the timeevolution of both volatile and non-volatile organic compounds and then theflavour profile of coffee brews.

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Exploring the link between coffee matrix microstructure and flow  properties using combined X-ray microtomography and smoothed particle  hydrodynamics simulations