When you pour water from a gooseneck kettle into a coffee bed, you are injecting kinetic energy into a porous medium. The physics begins with the jet break-up.
The Physics of Filter Coffee: Understanding the Science Behind the Perfect Brew
However, a grind that is too fine can lead to over-extraction and a bitter taste, while a grind that is too coarse can result in under-extraction and a weak flavor. The optimal grind size depends on factors such as the brewing method, the type of coffee beans, and the desired flavor profile.
Extraction is the physical process of moving soluble compounds from the solid coffee matrix into the liquid solvent (water). This occurs via two primary physical mechanisms: and diffusion . The Physics Of Filter Coffee Pdf
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After conducting a thorough search, I was able to find a few articles and research papers that discuss the physics of filter coffee. Here's a summary of one such article:
The definitive resource on this topic is the 2021 book The Physics of Filter Coffee When you pour water from a gooseneck kettle
Water must penetrate the microscopic pore network of the coffee cell walls, dissolve the trapped solubles, and transport them back out to the main fluid stream. Fick’s First Law of Diffusion
The rate of mass transfer depends on factors such as the surface area of the coffee particles, the flow rate and pressure of the water, and the solubility of the flavor compounds and oils. Optimizing these factors is crucial for achieving the perfect balance of flavor and aroma in the final brew.
Paper filters consist of cellulose fibers packed tightly together. Water moves through these microscopic gaps via capillary action, driven by surface tension and adhesive forces between the water and the cellulose. Chemical Adsorption The optimal grind size depends on factors such
Water displaces air within the porous coffee particles. Dissolution: Soluble compounds dissolve into the water.
Gravity pulls the coffee-enriched water through the filter. ⚖️ Key Physical Variables
For filter coffee, you want We < 10 to avoid droplet formation. A high We (caused by pouring from too high a height) creates micro-droplets that cool below optimal extraction temperature (90–96°C) before even reaching the coffee.
If you do not allow the bloom to finish (~30–45s of gas release), the trapped CO₂ prevents water from wetting the interior pores. The result is a gas-locked extraction—low TDS, high sourness.
) is rarely uniform across the entire coffee bed. If the coffee grounds are packed unevenly, or if the water is poured violently in one spot, the fluid will seek the path of least resistance.