The (developed by Dr. Ernest Lockhart at MIT in the 1950s) remains the standard graphical solution linking TDS, EY, and strength.
One of the most common defects in filter coffee is . When water finds a path of least resistance, it bypasses large sections of coffee grounds. This creates:
Freshly roasted coffee contains CO₂ trapped in the cellular matrix. When water hits the grounds, CO₂ escapes (the “bloom” phase). This gas blocks water from reaching particle surfaces. the physics of filter coffee pdf full
The coffee bed acts as a porous medium. Fluid dynamics within this medium are governed largely by , which describes the flow of a fluid through a porous material. $$Q = \frac-k A (P_b - P_a)\mu L$$ Where:
As grind size decreases, ( k ) drops dramatically. To maintain the same flow rate, you must either increase pressure (not possible in gravity brewing) or decrease the bed height (use less coffee). This is why espresso requires 9 bars of pressure—it forces water through fine particles. The (developed by Dr
The packing density of the coffee bed affects the resistance to flow and the extraction efficiency.
References:
Water has a high specific heat capacity (~4.18 J/g°C), meaning it carries significant thermal energy. When cold water first hits room-temperature grounds, a "thermal shock" occurs. The slurry temperature drops, slowing extraction. Thus, preheating the brewing device (e.g., ceramic dripper) and using a gooseneck kettle to maintain steady temperature are physical strategies to minimize heat loss.