Finer grinds increase exposed surface area, speeding extraction; coarser grinds slow it. Uniform particle size gives even extraction; a wide distribution causes under- and over-extracted pockets. Burr grinders yield better control than blades.
The physics of filter coffee can be modeled using mathematical equations, such as Darcy's law, which describes the flow of fluid through a porous medium. These models can be used to predict the optimal brewing conditions, such as the grind size, water temperature, and flow rate, to achieve the desired flavor and aroma.
The rate of chemical reactions (extraction of oils, acids, sugars) is temperature-dependent. This is described by the Arrhenius equation: The Physics Of Filter Coffee Pdf
The movement of solutes from the coffee particle to the water is governed by (steady-state diffusion):
The essay of physics continues into . The temperature of the water doesn't just affect how fast solids dissolve; it changes the viscosity of the water itself. Hotter water is less viscous, meaning it flows through the coffee bed faster. Gagné emphasizes that maintaining a stable temperature is vital because even a slight drop can shift the extraction profile, altering the delicate balance of flavors. Conclusion The physics of filter coffee can be modeled
The Physics of Filter Coffee - Jonathan Gagné - Google Books
The coffee grounds themselves also play a critical role in the brewing process. The size and distribution of the grounds affect the flow of water through the filter, as well as the surface area available for extraction. A finer grind will result in a slower flow rate and a more even extraction, while a coarser grind will produce a faster flow rate and a less even extraction. This is described by the Arrhenius equation: The
For a gooseneck kettle (D ≈ 0.005 m) pouring at 0.1 m/s, Re ≈ 500. This is well below the turbulent threshold (Re > 2000), resulting in a coherent, laminar stream. A laminar stream prevents air entrainment. If air bubbles are introduced into the slurry, they cause local chilling and inconsistent pressure gradients, leading to uneven extraction.