Title: How Earth Science Inspired a New Equation for Coffee Water Flow Speed

Researchers have developed a physics-based equation to help baristas and coffee enthusiasts achieve the perfect espresso shot by optimizing water flow through ground coffee.

The discovery, reported in the April 1 issue of Royal Society Open Science, draws inspiration from earth science principles governing how gases move through volcanoes and how water flows through the Earth’s crust. Fabian Wadsworth, an earth scientist at Ludwig-Maximilians-Universität München in Germany, led the research after recognizing that coffee brewing offered an accessible way to teach fundamental concepts of percolation to students.

According to Wadsworth, crafting a quality espresso requires two key factors. First, the ground coffee must be evenly distributed and uniformly tamped into a compact puck to prevent uneven water flow. An uneven puck creates channels where water flows more quickly through some areas while bypassing others, leading to under-extraction in dense regions and over-extraction in channels.

The second critical factor is controlling the time water spends in contact with the coffee particles. The equation developed by the research team calculates the speed of water percolation through the coffee bed, allowing precise adjustment of brewing variables. When the coffee puck is too densely packed, water moves slowly, increasing contact time and risking a bitter brew from over-extraction. Conversely, if the puck is too loose, water passes through too quickly, resulting in under-extraction that fails to draw out sufficient flavor and caffeine.

The research builds on established principles of fluid dynamics and granular material behavior, fields that have long studied how liquids interact with packed particles in geological and industrial contexts. By applying these concepts to coffee brewing, the scientists have created a practical tool that translates complex physics into actionable guidance for both professional baristas and home enthusiasts seeking consistency in their espresso preparation.

While the equation provides a scientific framework for optimizing extraction, Wadsworth emphasizes that achieving the perfect shot still requires attention to bean quality, roast level, and water temperature—factors that interact with the physical dynamics of percolation. The research does not claim to eliminate the artistry of coffee making but rather to enhance it with a deeper understanding of the underlying physical processes.