ABSTRACT

Espresso extraction is a complex process involving water flow through a porous medium undergoing time-dependent geometric changes, solubilisation of hydrophilic substances, emulsification of insoluble coffee oils and suspension of coffee cell-wall fragments ("fines"). In this talk I will discuss the effects of changing porous bed micro-morphology on the extraction kinetics. We devise mesoscopic flow models in the framework of smoothed particle hydrodynamics (SPH) [1] to model fines migration, particle erosion, and particle swelling. It is found that fines migration leads to a transient permeability for the porous matrix, and results in an increase of compound content in the cup [1]. Particle erosion induced by the mechanical force of flow leads to channelisation phenomenon and, if the erosion is pressure-dependent, heterogeneity in the filtration direction will also be induced [2]. These findings have been recently reported in X-ray microCT analysis of coffee capsules pre/post extraction and fully-resolved SPH simulations [3]. Another feature that must be considered in coffee extraction is particle swelling which can affect both the intra-granular and inter-granular transport of the soluble compounds. Even a very small degree of coffee particle swelling will significantly enhance the compound content in the cup, potentially altering taste and aroma of the espresso. I will discuss a swelling model incorporated in SPH to describe the above mentioned phenomenology [4]. Finally, a reduced-order 1D model of coffee extraction will be proposed for fast simulations, retaining the main physical mechanisms of the extraction process, and allowing the study of extraction kinetics under pressure or flow-rate controlled conditions [5].

References

1. M Ellero, L Navarini. "Mesoscopic modelling and simulation of espresso coffee extraction" J Food Engng, 263, 181–194 (2019).

2. C Mo, L Navarini, FS Liverani, M Ellero, "Modeling the effect of flow-induced mechanical erosion during coffee filtration" Physics of Fluids, 33(9) (2021).

3. C Mo, R Johnston, L Navarini, FS Liverani, M Ellero, "Exploring the link between coffee matrix microstructure and flow properties using combined X-ray microtomography and smoothed particle hydrodynamics simulations", Sci. Rep. 13, 16374 (2023).

4. C Mo, L Navarini, FS Liverani, M Ellero, "Modeling swelling effects during coffee extraction with smoothed particle hydrodynamics". Physics of Fluids, 34(4), 043104 (2022).

5. C Mo, L Navarini, FS Liverani, M Ellero, Modelling swelling effects in real espresso extraction using a 1-dimensional coarse-grained model" J Food Engng 365, 111843 (2024)

SPEAKER CV

Marco Ellero is Ikerbasque Professor of Computational Fluid Dynamics at the Basque Center for Applied Mathematics in Bilbao where he is the main coordinator of the Area “Computational Mathematics” and Head of the research line “CFD: modelling and simulation”. He is also currently Honorary Professor in the Zienkiewicz Centre for Computational Engineering (ZCCE) and Complex Fluids Research Group at Swansea University as well as member of the Institute of Non-Newtonian Fluid Mechanics (INNFM, UK). His research interests deal with the theoretical modelling and numerical simulation of complex fluids, particulate systems and multiscale flow phenomena with particular focus on biofluid mechanics, microfluidics and rheology. The main goal of Prof. Ellero’s work is the development of new models based on Lagrangian multiscale particle-methods and the design of efficient parallel algorithms for the analysis of complex flows.