Under Pressure: Poroelastic Regulation of Flow in Espresso Brewing

A University of Warsaw team has shown that the coffee puck behaves as a poroelastic material under the six-to-nine-atmosphere pressures typical of espresso extraction. The study, soon to appear in *Physics of Fluids*, shows that elastic compaction creates a nonlinear pressure-flow relationship, contradicting the linear Darcy-law model long used to describe water movement through coffee. This feedback loop generates channeling, where water follows weakened pathways and produces uneven flavor extraction.

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The work was led by physicist Maciej Lisicki with co-authors R. Waszkiewicz, F. Myck, L. Bialas, M. Puciata-Mroczynska, M. Dzikowski and P. Szymczak of the University of Warsaw. It was accepted for publication on 23 June 2026 in *Physics of Fluids*. Experiments involved hundreds of 30–40 second brews recorded with real-time pressure sensors. Results revealed that increasing pressure beyond the typical range yields diminishing increments in flow rate, confirming a nonlinear pressure-flow curve driven by poroelastic compaction.

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The findings suggest that baristas could improve consistency by adjusting tamping pressure, grind size, or extraction time according to poroelastic principles rather than relying solely on pressure magnitude. Manufacturers may adopt adaptive pressure profiles that respond to real-time flow feedback, reducing channeling. Outside the coffee sector, the research offers a concrete example of fluid-structure interaction in soft porous media, relevant to geophysics, biomedical engineering and chemical processing.

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The authors describe their approach as “a systematic series of espresso brews with real-time pressure sensing that illuminates how poroelastic compaction governs extraction dynamics.” They emphasize that their coarse-grained model “captures the nonlinear relationship between applied pressure and flow through the coffee puck.” The team notes plans to use transparent bead-packed analogues to visualize compaction patterns and extend the theoretical framework.

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• “As Maciej Lisicki, lead author, eloquently puts it: coffee provides mysteries as profound as galaxies, inviting scientific curiosity and innovation alike.” — Maciej Lisicki, lead author

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• “Each cup of espresso embodies a delicate balance of forces and material properties, orchestrated through precise timing, pressure, and flow.” — Research team (article conclusion)

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• “The interplay between flow-induced deformation and fluid dynamics is a classic problem in porous media, relevant to geophysics, biomedical engineering, and chemical processing.” — Article text

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• “Machine manufacturers might optimize pressure profiles or introduce adaptive controls that modulate applied force to maintain ideal flow conditions, mitigating channeling and promoting uniform extraction.” — Research outlook

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The researchers intend to build transparent experimental cells filled with glass beads that mimic coffee grounds, enabling direct imaging of flow channels and compaction zones. Successful visualization would refine the model and guide design of next-generation espresso machines with feedback-driven pressure regulation.

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