New equation predicts espresso coffee puck permeability
Get the Health newsletter
Daily health & science — research, biotech, public health, the studies worth knowing. Free.
- Fabian B. Wadsworth and colleagues published a permeability model in Royal Society Open Science (DOI: 10.1098/rsos.252031) that predicts how water flows through the bed of tightly packed coffee grounds used to pull an espresso shot
- Tumba (Rwanda) and Guayacán (Colombia) coffee samples were ground into 11 sizes and scanned with X-ray computed micro-tomography to build 3D maps of the pore tunnels and gaps between grains
- The model applies percolation theory from physics, finding permeability depends on connected pore space, total grain surface area, average grain size, and how tightly the grounds are packed
- Permeability sets flow rate and water-ground contact time, which the researchers say directly determines how much flavor ends up in the cup
- The team acknowledged that particle swelling once coffee gets wet remains unmodeled and flagged it as needing further study
- The researchers suggested the framework could eventually help engineers design smart espresso machines that automatically adjust grind and packing to different beans
Why it matters: Espresso preparation has long been managed by feel — baristas tweak grind and tamp to hit a target flow rate without a predictive model. This study delivers the first equation grounded in XCT imaging of real coffee pucks and percolation theory, giving the specialty coffee industry a physics-based tool to standardize extraction. The caveat: the team admits wet-grain swelling is still unmodeled, so practical adoption in cafes or machines is not imminent.
