espresso percolation – New research links espresso quality to percolation physics—quantifying how fast water flows through tamped grounds and how grain size changes permeability.
A great espresso can feel like art, but the mechanics of how water moves through coffee are governed by physics.
Coffee starts with ground beans packed into a puck by tamping.. Then hot, pressurized water moves through that dense layer, pulling out compounds that create flavor, bitterness and caffeine.. Misryoum reports that researchers have turned the coffee puck into a system that behaves like other “percolation” problems seen in nature—where fluids find pathways through complicated. porous material.
The new work draws inspiration from volcanology, where scientists study how gases and fluids travel through rock.. Fabian Wadsworth. an earth scientist. says he became interested in percolation physics partly as a teaching tool—using coffee as a way to make fundamental ideas more engaging for students.. The approach is simple in concept: if you can describe how fluid speed changes as it passes through a porous bed. you can connect process choices to taste.
A key message is that “quality” begins before water arrives.. Wadsworth argues that the grounds must be even and the puck should be tamped uniformly.. If one region of the puck is looser or clumped. water will preferentially flow through it. bypassing other areas and reducing extraction.. In other words, unevenness doesn’t just change appearance or texture—it changes where water spends time.
The second lever is time.. The model emphasizes controlling how long water remains in contact with the coffee particles.. In a denser puck, water moves more slowly, extending contact time.. Too long can push extraction toward bitterness; too short leaves flavor and caffeine underdeveloped.. Misryoum highlights that these outcomes aren’t random: they follow from how flow speed and contact duration interact inside the packed grounds.
Turning volcanology equations into espresso guidance
After establishing the assumption that the grounds are evenly distributed and tamped with equal pressure. the researchers propose an equation that can calculate flow speed through the coffee bed.. The point isn’t to replace barista skill with a single number. but to give the process a quantitative language—one that can describe percolation in the same way other studies describe gas flow in magma pathways or water transport through sandstone.
To test whether the equation holds up. Wadsworth and colleagues examined coffee from two origins—Tumba from Rwanda and Guayacán from Colombia.. They prepared samples by grinding each roast at 11 different settings, producing 22 total ground materials.. Instead of relying only on brew outcomes. they used imaging and modeling: software that converts multiple X-ray cross sections into three-dimensional renderings to track how fluid moved through the samples.
Why grind size could matter more than you think
The results point to a broader implication for espresso and beyond: the physics-based model can describe percolation through coffee grounds with similar clarity to how it describes other porous media.. That matters because coffee is not uniform.. Particle size, packing structure, and the resulting permeability—how easily fluid passes through the bed—shape the brewing pathway.
Grain size, in particular, can strongly affect permeability, which Misryoum notes as a direct route to changes in taste.. The researchers report that doubling grain size increases permeability by a factor of four.. That kind of relationship is exactly what a percolation framework is built to capture: small changes in the structure of a porous medium can produce larger shifts in fluid motion.
This also helps explain why “same recipe, different grinder” can yield very different cups.. If coarser grounds alter permeability dramatically, then water speed through the puck changes, and with it the effective extraction time.. The model offers a way to think about those differences without treating them as mysterious craftsmanship alone.
From barista technique to measurable percolation
Wadsworth suggests the equation will be most useful when paired with equipment capable of measuring pressure and flow rates during brewing.. Many espresso machines don’t currently communicate that level of detail to users.. But in the future. pressure and flow data could make it easier to translate technique variables—like grind adjustment and tamp consistency—into measurable changes in percolation speed.
This is where the research feels unusually practical.. Instead of debating only roast profiles or “feel. ” baristas could use a shared framework to interpret what happens inside the puck.. A machine that measures flow and pressure would effectively let the espresso process speak in the same terms as the model: how quickly water moves through a porous bed under pressure.
The human impact is straightforward: improved repeatability.. Espresso is famously sensitive to tiny changes. and that can frustrate people who want stable results at home or in a café.. A physics-based approach won’t eliminate nuance. but it can reduce guesswork by linking observable process choices to the underlying transport dynamics.
And there’s an environmental angle worth keeping in view.. Better process control can mean fewer wasted attempts. less trial-and-error grinding. and more efficient use of coffee—an increasingly important consideration as supply chains face volatility.. Physics won’t solve sustainability by itself, but it can make consumption more deliberate.
For coffee science. Misryoum sees this as part of a broader trend: methods developed in one field—here. volcanology’s understanding of fluid pathways through complex materials—finding their way into everyday technologies.. The percolation equation is not just a curiosity.. It’s a reminder that the most memorable moments. from the crema topping a morning cup to the quiet swirl of a portafilter. are built on systems that can be measured. modeled and improved.