Coffee extraction is the process of chemical release from a compound-rich (i.e. caffeine, trigonelline etc.) porous solid phase (the coffee bed, Fig. 1) into a pressure-driven flowing fluid. It involves many complex physical and transport processes extremely difficult to model. Among the many factors that will affect the final quality of coffee, the microstructure of the coffee matrix is one of the most critical ones. This is not simply because of the multiscale topological features of the coffee bed geometry, but also several other physical effects. For example, during the 30s espresso brewing time the porous medium undergoes geometric changes due to coffee fragments migration, the particle erosion, as well as particle swelling. In addition, there is solubilization of hydrophilic substances, emulsification of insoluble coffee oils, suspension of solid coffee cell-wall fragments (fines) and CO2 degassing involved in foam formation. These physical processes are all interconnected, rendering the modelling of coffee extraction very challenging. In this research line, we explore some of these processes by mean of theory, particle-based fluid dynamics simulations as well as X-ray micro-computed (microCT) techniques.
Particle migrations
Ellero, M. and L. Navarini (2019). Mesoscopic modelling and simulation of espresso coffee extraction. Journal of Food Engineering 263, 181194. doi
Particle erosion
Mo, C., R. Johnston, L. Navarini, and M. Ellero (2021). Modeling the flow through erodible porous media with smoothed dissipative particle dynamics. Physics of Fluids 33 (9), 093101. doi
C Mo, R Johnston, L Navarini, FS Liverani, M Ellero (2023), Exploring the link between coffee matrix microstructure and flow properties using combined X-ray microtomography and smoothed particle hydrodynamics simulations, Scientific Reports 13, 16374. doi
Particle swelling
Mo, C., R. Johnston, L. Navarini, and M. Ellero (2022). Modelling swelling effects during coffee extraction with smoothed particle hydrodynamics. Physics of Fluids 34 (4), 043104. doi
C Mo, L Navarini, F Suggi-Liverani, M Ellero (2023), Modelling swelling effects in real espresso extraction using 1-dimensional coarse-grained model, J. Food Engng. 111843 . doi