Many coffee enthusiasts swear by the pour-over coffee process. (Photo by Auttapol Sangsub on Shutterstock)
In a nutshell
- Higher pours = stronger coffee: Pouring from greater heights creates more turbulence and better mixing, yielding stronger brews without using more beans.
- Avalanche physics: Water jets create “avalanche dynamics” in coffee grounds, causing waves of mixing that continuously expose fresh grounds to water.
- Pour slower for better results: Thinner, slower water streams allow longer contact time between water and coffee, potentially improving extraction efficiency.
PHILADELPHIA — Your morning coffee ritual might be getting a scientific upgrade. Researchers from the University of Pennsylvania have found that simply changing how high you hold your kettle can dramatically improve your pour-over coffee’s strength—without using more precious beans.
Pour-over coffee brewing—where hot water flows from a specialized kettle onto coffee grounds in a cone-shaped filter—has exploded in popularity among coffee enthusiasts. While baristas and home brewers have developed theories about the “perfect pour,” scientific evidence for these methods has been largely missing until now.
The study, published in the journal Physics of Fluids, uncovers the physics behind what makes pour-over coffee extract more efficiently. The team discovered that pouring water from greater heights increases granular agitation, leading to stronger mixing and extraction.
Coffee, of course, is one of the most popular drinks around the world, with over 10.5 billion kilograms consumed in 2021-2022 alone. For many, it’s as necessary to get through the day as air. But the Arabica coffee plant, which accounts for most high-quality coffee, is increasingly threatened by rising global temperatures.
“With the changing climate, it is becoming more difficult to grow coffee. However, this paper demonstrates a potential method to decrease the quantity of coffee beans required to brew a pour-over coffee, simply by changing the way in which one pours the liquid jet,” the researchers write in their paper.
Study authors weren’t just interested in making better coffee. They wanted to find ways to get more flavor out of fewer beans—potentially helping address looming shortages in coffee supply. Using a combination of transparent models and real coffee experiments, they revealed surprising physics at work beneath the surface of your morning brew.
“Instead of increasing the amount of beans, the sensory profile and the strength of the beverage can be adjusted by varying the flow rate and the pour height,” the researchers explain. In other words, how you pour actually matters just as much as what you pour.
The scientists substituted clear silica gel particles for opaque coffee grounds to visualize exactly what happens when water hits coffee. Using high-speed cameras and laser imaging, they tracked particle movement as water flowed into their model coffee maker at various heights.
What they discovered was unexpected. When water is poured from higher positions, it creates what scientists call “avalanche dynamics” in the coffee bed. This avalanching effect constantly stirs the coffee particles in waves, allowing water to extract more flavor compounds.
The team found that with a standard-thickness water jet (like what comes from most gooseneck kettles), higher pour heights consistently produced stronger coffee. With thin water streams, the height mattered less—but the slower flow rate still yielded excellent extraction.
Perhaps most surprising was their discovery that the common “floating raft” of coffee grounds—those annoying bubbles and floating particles during brewing—doesn’t significantly affect the mixing process. The physics happening beneath the surface matters far more.
The experiment also shows what happens at the bottom of the coffee cone. For thicker water streams, lower pour heights could dig deeper into the bed of grounds. However, this didn’t translate to better extraction efficiency, as measured by total dissolved solids. The researchers determined that the overall mixing and avalanching throughout the brewing process had a much greater impact on the final cup.
The team verified their findings by brewing actual coffee at different pour heights and measured the total dissolved solids—essentially, how much coffee got extracted into the water. The results confirmed their model: higher pours with standard water flow produced significantly stronger brews without using additional coffee.
This research offers insights that go well beyond the kitchen counter. The same physics applies to environmental concerns like dam erosion, waterfall impact on rocks, and even wastewater treatment. But for coffee lovers, the takeaway is simple: how you pour matters.
As climate change continues threatening coffee production globally, these findings offer a practical way to get more flavor with fewer beans. By slightly adjusting your morning ritual—holding your kettle higher and pouring more slowly—you might help conserve a beloved but increasingly vulnerable resource while enjoying a more flavorful cup.
Paper Summary
Methodology
To understand what happens during a pour-over, the researchers created a laboratory setup that allowed them to see inside the brewing process. They used a transparent glass funnel similar to popular V60 brewers and replaced the opaque coffee grounds with transparent silica gel particles with similar size distributions to actual coffee grounds (0.2-1 mm). A high-speed camera captured the action at 200 frames per second while a laser sheet illuminated the particles, allowing researchers to visualize the internal dynamics of the brewing process.
The scientists controlled water flow using a carboy with tube outlets of different diameters (1/4-inch and 1/8-inch) to simulate different pour rates typical of gooseneck kettles. They varied the pour height by adjusting the position of the funnel relative to the water outlet while maintaining consistent water levels. For experiments involving a floating layer of grounds, they added small polystyrene beads to mimic the floating coffee grounds often seen during brewing. In the final phase, they conducted experiments with actual coffee (Simply Nature Organic Honduras beans) to measure total dissolved solids in the resulting brew under different pouring conditions.
Results
The researchers discovered several key findings that coffee enthusiasts might find surprising. First, they established that the “mixing index” (a measure of agitation in the water layer above the coffee bed) generally increased with pour height, contradicting the common belief that higher pours might be less effective due to increased air entrainment in the water stream. For a typical gooseneck kettle with a 1/4-inch outlet, higher pours consistently produced more agitation and mixing.
Second, the team found that the floating layer of grounds that often forms during brewing had minimal impact on mixing patterns, despite conventional wisdom suggesting it might interfere with water flow. Their experiments with and without a floating granular raft showed similar mixing patterns at various pour heights.
Third, they discovered that lower pour heights were actually better at “digging” into the coffee bed and reaching the bottom of the cone, which they measured as a “density index.” This creates a counterintuitive trade-off between mixing at the top (better with higher pours) and erosion at the bottom (better with lower pours).
Most importantly, they observed a rhythmic “avalanche dynamic” where the water jet would erode the granular bed, hollow it out, cause grounds to accrete at the edges, and then trigger periodic collapses that would restart the cycle—a previously undescribed mechanism that promotes continuous mixing throughout brewing.
When testing with real coffee beans, they confirmed that higher pours with thicker water jets produced stronger brews with more dissolved solids. With thinner water jets (slower pours), the extraction was generally high across all pour heights, likely due to the longer brewing time required to reach the target volume.
Limitations
This research, while groundbreaking, does have several limitations worth noting. The study focused primarily on a single size distribution of particles and a specific cone angle (60 degrees), which might not perfectly represent all pour-over setups. The researchers acknowledged that different grind sizes could potentially change the dynamics, requiring further investigation.
Temperature effects, which can significantly impact extraction chemistry, were not fully explored in this study. The researchers noted that while brew temperature affects which compounds are extracted, the physical dynamics of the avalanche effect likely operate independently of temperature.
The model system using silica gel particles, while visually informative, couldn’t perfectly replicate the absorption, blooming, and chemical extraction properties of actual coffee grounds. Additionally, the experiments were conducted with a plugged outlet rather than allowing continuous flow through a filter, which might alter the dynamics in typical brewing scenarios.
Finally, the study didn’t fully explore the full range of pouring parameters that might affect extraction, such as pouring patterns (circular versus center pours), different filter materials, or the impact of the initial bloom time on subsequent extraction.
Funding and Disclosures
The research was funded by the Charles E. Kaufman Foundation through an Early Investigator Research Award (KA2022-129523). This study was part of the “Kitchen Flows 2024” special topic collection in Physics of Fluids, highlighting the intersection of fluid dynamics and everyday food preparation. The authors declared no conflicts of interest.
Publication Details
The paper titled “Pour-over coffee: Mixing by a water jet impinging on a granular bed with avalanche dynamics” was authored by Ernest Park, Margot Young, and Arnold J.T.M. Mathijssen from the Department of Physics and Astronomy at the University of Pennsylvania. It was published in Physics of Fluids (Volume 37, Issue 043332) on April 8, 2025. The paper was submitted on January 13, 2025, accepted on February 11, 2025, and published online on April 8, 2025. It can be accessed using the DOI: 10.1063/5.0257924.
Or, you can keep a spoon nearby your pouring over station and agitate your coffee while it brews