estimating the steady-state permeability of coffee grounds

Article Review

Overview

The authors of this article were investigating the permeability of beds of spent coffee grounds. They measured pressure drop at various flow rates and determined the permeability using Darcy’s law (reporting permeability values in the range of 10-13-10-14 m2. They also estimated a “theoretical permeability” from particle size distributions using the Kozeny-Carman equation, but found that these did not correlate well with the empirical values. The author’s suggested that this might be explained if bed consolidation had effect on the packing structure beyond merely decreasing the bed bulk porosity. They modified Kozeny-Carman equation to include a porosity-dependent tortuosity factor which was reported to provide a better fit of the empirical permeability data.

 

My thoughts

I really enjoyed reading this article, although at 61 pages it’s not a quick read! The introduction presents some views of the coffee science literature surrounding espresso brewing parameters which I completely agree with – I lot of other papers I have read have failed to address a key variable (flow) and often ignore the interdependence between it, grind size and pressure.

 

Details

Title: A new methodology to estimate the steady-state permeability of roast and ground coffee in packed beds
Author(s): B.R. Corrochano, J.R. Melrose, A.C. Bentley, P.J. Fryer, S. Bakalis
Published: November, 2015
Link: View the full article on ResearchGate.net

Citation

Corrochano, B.R., Melrose, J.R., Bentley, A.C., Fryer, P.J., Bakalis, S., A new methodology
to estimate the steady-state permeability of roast and ground coffee in packed beds, Journal of Food Engineering
(2014), doi: http://dx.doi.org/10.1016/j.jfoodeng.2014.11.006

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