Porosity ($\epsilon$) is the fraction of the total bed volume that is void space: $$ \epsilon = \fracV_voidsV_total $$ In a dry bed, this is inter-particle porosity. Upon wetting, the bed swells (hydraulic expansion), altering the geometry. The permeability ($k$) of this porous medium dictates the ease with which fluid passes, described by the Kozeny-Carman equation: $$ k = \frac\epsilon^3K (1-\epsilon)^2 S_v^2 $$ Where $K$ is the Kozeny constant. This equation highlights a critical non-linear relationship: a small decrease in particle size (increasing $S_v$) drastically reduces permeability, leading to increased brew time or stalling.
: Bitterness, astringency (tannins and heavier compounds dissolved). 🛠️ Key Variables for Research Physical Effect Grind Size Surface Area Smaller grinds = faster diffusion. Water Chemistry Ion Interaction Magnesium and Calcium ions pull more flavor. Turbulence Kinetic Energy Stirring breaks the stagnant boundary layer. Contact Time Longer time = more heavy-molecule extraction. the physics of filter coffee epub work
Enter The Physics of Filter Coffee by astrophysicist (and coffee obsessive) Jonathan Gagné. This isn’t your typical glossy coffee table book. It’s a 300-page love letter to fluid dynamics, thermodynamics, and particle size distribution. And yes, it works brilliantly as an EPUB. Porosity ($\epsilon$) is the fraction of the total