For a better cup of coffee, look to physics

Researchers from Penn have found new cost-effective ways to make a great cup of pour-over coffee using fewer beans. Their findings could potentially provide insights into similar systems such as waterfalls and surface erosion.

University of Pennsylvania

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A high-speed camera catches water penetrating the simulated coffee bed. By modeling how the jet interacts with the grounds, the team found the most efficient flow pattern for extracting flavor with fewer beans.

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Credit: Ernest Park

The cost of raw arabica beans, the core component of most coffee, has spiked in recent years due to four consecutive seasons of adverse weather. Climate change has added further strain, threatening the delicate temperature balance required by the Coffea arabica plant. This growing pressure has inspired physicists at the University of Pennsylvania to ask: Can we make great coffee with fewer beans?

“There’s a lot of research on fluid mechanics, and there’s a lot of research on particles separately,” says Arnold Mathijssen, assistant professor in the School of Arts & Sciences. “Maybe this is one of the first studies where we start bringing these things together.”

Their findings, published in the journal Physics of Fluids, provide a scientific approach to improving extraction efficiency so fewer coffee grounds can go further without diminishing overall quality.

“We tried finding ways where we could use less [or] as little coffee as possible and just take advantage of the fluid dynamics of the pour from a gooseneck kettle to increase the extraction that you get from the coffee grounds—while using fewer grounds,” says coauthor Ernest Park, a graduate researcher in the Mathijssen Lab.

The experiment required making the invisible visible, explains coauthor Margot Young, a graduate researcher in the Mathijssen Lab.

“Coffee’s opacity makes it tricky to observe pour-over dynamics directly, so we swapped in transparent silica gel particles in a glass cone,” Park explains.

A laser sheet and high-speed camera allowed them to watch water streams create “miniature avalanches” of particles—revealing the flow’s inner workings. Water poured from a height produces the avalanche effect that stirs the bed of particles and enhances extraction.

A key factor in this process is laminar, or smooth and nonturbulent flow—made possible by a gooseneck kettle, even with a gentle pour-over flow. “If you were just to use a regular water kettle, it’s a little bit hard to control where the flow goes,” says Park. “And if the flow isn’t laminar enough, it doesn’t dig up the coffee bed as well.”

The team discovered that when water is poured from a height, it creates a stronger mixing effect.

“When you’re brewing a cup, what gets all of that coffee taste and all of the good stuff from the grounds is contact between the grounds and the water,” explains Young. “So, the idea is to try to increase the contact between the water and the grounds overall in the pour-over.”

They found that if poured from too great a height, the water stream breaks apart into droplets, carrying air with it into the coffee cone, which can actually decrease extraction efficiency.

The researchers conducted additional experiments with real coffee grounds to measure the extraction yield of total dissolved solids. Their results confirmed that the extraction of coffee can be tuned by prolonging the mixing time with slower but more effective pours that utilize avalanche dynamics.

For thicker water flow, they found that higher pours resulted in stronger coffee, confirming their observations about increased agitation with higher pour heights. When using a thinner water jet, the extraction remained consistently high across different pour heights, possibly due to the longer pouring time required to reach the target volume.

Broad implications that extend beyond the kitchen

The study is a love letter to coffee—and it’s also a window into the team’s broader research. “We weren’t just doing this for fun,” Mathijssen says. “We had the tools from other projects and realized coffee could be a neat model system to explore deeper physical principles.”

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Those principles extend well beyond the kitchen, notes Young. “This kind of fluid behavior helps us understand how water erodes rock under waterfalls or behind dams,” she says. Even wastewater treatment and filtration systems involve similar dynamics, Mathijssen adds.

The project also reflects ongoing research in the lab, as Park is working on microscale active surfaces that use rotating magnetic fields to clean biofilms from medical devices.

Young, meanwhile, is investigating ultra-fast biological flows, using the same high-speed imaging setup to study how tiny vortices generated by lung cilia help clear pathogens.

“You can start small, like with coffee,” Mathijssen says. “And end up uncovering mechanisms that matter at environmental or industrial scales.”

Arnold Mathijssen is an assistant professor in the Department of Physics & Astronomy in the School of Arts & Sciences at the University of Pennsylvania.

Ernest Park is a Ph.D. candidate in the School of Arts & Sciences.

Margot Young is a Ph.D. candidate in the School of Arts & Sciences.

The research was supported by the Charles E. Kaufman Foundation (Award KA2022-129523).

In the Arnold Mathijssen lab, researchers used a gooseneck kettle, coffee grinder, and a pour-over setup alongside precise measurements and high-speed analysis to study the fluid dynamics and mechanics of coffee brewing to uncover ways to maximize flavor with fewer grounds. The findings could help researchers understand fluid dynamics.

To pinpoint pour-over variables affecting taste, the team recorded each brew’s temperature, weight, grind size, and extraction time—then rated the results for flavor. Precision scales and detailed lab notes were key to translating fluid dynamics into a better cup of coffee.

Slow-mo pour-over coffee 2 [VIDEO] | 

A high-speed camera catches water penetrating the simulated coffee bed. By modeling how the jet interacts with the grounds, the team found the most efficient flow pattern for extracting flavor with fewer beans.

Credit

Ernest Park

Journal

Physics of Fluids

DOI

10.1063/5.0257924 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Pour-over coffee: Mixing by a water jet impinging on a granular bed with avalanche dynamics featured

Article Publication Date

8-Apr-2025

 

Light that spirals like a nautilus shell

‘Optical rotatum’ describes new structure of light

Peer-Reviewed Publication

Harvard John A. Paulson School of Engineering and Applied Sciences

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The optical rotatum's logarithmic spiral follows a pattern found often in nature, including nautilus shells.

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Credit: Capasso Lab / Harvard SEAS

Beams of light that can be guided into corkscrew-like shapes called optical vortices are used today in a range of applications. Pushing the limits of structured light, Harvard applied physicists in the John A. Paulson School of Engineering and Applied Sciences (SEAS) report a new type of optical vortex beam that not only twists as it travels but also changes in different parts at different rates to create unique patterns. The way the light behaves resembles spiral shapes common in nature. 

The researchers borrowed from classical mechanics to nickname their never-before-demonstrated light vortex an “optical rotatum,” to describe how the torque on the light’s corkscrew shape gradually changes. In Newtonian physics, “rotatum” is the rate of change in torque on an object over time.

The optical rotatum was created in the lab of Federico Capasso, the Robert L. Wallace Professor of Applied Physics and the Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS. “This is a new behavior of light consisting of an optical vortex that propagates through space and changes in unusual ways,” Capasso said. “It is potentially useful for manipulating small matter.” The research is published in Science Advances.

In a peculiar twist, the researchers found that their orbital angular momentum-carrying beam of light grows in a mathematically recognizable pattern found all over the natural world. Mirroring the Fibonacci number sequence (made famous in The Da Vinci Code), their optical rotatum propagates in a logarithmic spiral that is seen in the shell of a nautilus, the seeds of a sunflower, and the branches of trees.  

“That was one of the unexpected highlights of this research,” said first author Ahmed Dorrah, a former research associate in Capasso’s lab, now an assistant professor at Eindhoven University of Technology. “Hopefully we can inspire others who are specialists in applied mathematics to further study these light patterns and gain unique insights into their universal signature.”

The research builds on previous work in which the team used a metasurface, a thin lens etched with light-bending nanostructures, to create a light beam with controlled polarization and orbital angular momentum along its propagation path, converting any input of light into other structures that change as they move. Now, they’ve introduced another degree of freedom to their light, in which they can also change its spatial torque as it propagates.

“We show even more versatility of control, and we can do it continuously,” said Alfonso Palmieri, a graduate student in Capasso’s lab and co-author of this research.

Potential use cases for such an exotic beam of light include the control of very small particles, such as colloids in suspension, by introducing a new type of force in accordance with the light’s unusual torque. It could also enable a precise optical tweezer for micro-manipulation of small things.

While others have demonstrated torque-changing light using high-intensity lasers and bulky setups, the Harvard team made theirs with a single liquid crystal display and a low-intensity beam. By showing they can create a rotatum in an industry-compatible, integrated device, the barrier to entry for their technology to become reality is much lower than previous demonstrations.

The paper was co-authored by Lisa Li in the Capasso Group. Federal funding for this research came from the Office of Naval Research MURI program under grant No. N00014-20-1-2450 and the Air Force Office of Scientific Research under grant No. FA9550-22-1-0243.

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Journal

Science Advances

DOI

10.1126/sciadv.adr9092 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Rotatum of light

Article Publication Date

11-Apr-2025

 

New research shows evidence of children’s gender biases reflected in their facial emotional expressions

University of Toronto

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New research recently published in Archives of Sexual Behavior suggests children’s gender biases can be reflected in their facial emotional expressions.   

Psychology professor Doug VanderLaan and his colleagues at the University of Toronto Mississauga, studied 296 children (148 boys and 148 girls) in Canada between the ages of four and nine years old while Wang Ivy Wong, Karen Kwan and their colleagues at the Chinese University of Hong Kong, and The Hong Kong Polytechnic University studied 309 children (155 boys and 154 girls) in Hong Kong. All children watched four short stories that included five illustrations with pre-recorded audio narratives. The stories were presented in random order and showed peers who were in the same grade as the participant and displayed behaviours that either did or did not follow gender stereotypes. While viewing the stories, FaceReader software was used to code the intensities of participants’ emotions, including angry, disgusted, happy, sad, scared, and surprised.  

The study found a small effect for one emotional expression (fear), but little to no difference in emotion with the other five. Participants displayed more scared emotion when viewing a boy who wasn’t following societal gender stereotypes in the types of toys, activities, clothes, hairstyles, and friends he preferred. This fear was correlated with one of five verbal questions, in particular a question related to emotion perception, where children shared that they perceived the feminine-behaving boy as being less happy when compared with the boy who conformed with masculine gender stereotypes.“These results provide evidence that children’s gender biases are reflected in their facial emotional expressions – specifically showing signs of being scared when it comes to boy peers whose behaviours don’t follow gender stereotypes,” said Doug VanderLaan, an associate professor with the Department of Psychology at the University of Toronto Mississauga. “Developmentally, children may learn to imitate such fear responses from those who are around them like their peers, family members, and media.” 

VanderLaan noted the finding is consistent with other studies highlighting that less positive characteristics are assigned to children whose behaviours don’t follow gender stereotypes, especially when it comes to feminine-behaving boys. However, for this study in particular, examining facial emotional expressions provided unique insights into the emotional component of peer appraisals. Overall, the research contributes toward more complete understanding when it comes to children’s gender biases while assessing their peers.   

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Journal

Archives of Sexual Behavior

DOI

10.1007/s10508-025-03113-6 

Method of Research

Observational study

Subject of Research

People

Article Title

Children’s Facial Emotional Expressions to Gender-Nonconforming Hypothetical Peers

Article Publication Date

10-Apr-2025

 

Crustal brines at an oceanic transform fault

New research explores geological processes along plate boundaries

Woods Hole Oceanographic Institution

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Assembling an ocean-bottom electromagnetometer, a receiver that records electric and magnetic fields.

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Credit: ©Paige Koenig, co-author

Woods Hole, Mass. (April 11, 2025) - Being a geophysicist can sometimes feel like being a detective —uncovering clues, and then building a case based on the evidence.

In a new article published in Science Advances, a collaborative team led by the Woods Hole Oceanographic Institution (WHOI), presents a never-before-seen image of an oceanic transform fault from electromagnetic (EM) data collected at the Gofar fault in the eastern Pacific Ocean. The National Science Foundation funded work reveals unexpected brine deposits beneath the seafloor near the fault, which could change the way we conceptualize oceanic transform faults.

The Gofar fault operates much like the San Andreas, in that two tectonic plates slide sideways past each other. Unlike the San Andreas, large earthquakes on this fault have been strangely predictable, with large ruptures occurring every five to six years. That predictability has made Gofar an ideal place to study earthquake mechanisms, with a variety of data collected at the fault, including a number of small earthquakes measured on ocean bottom seismographs.

In contrast to seismic data, EM measurements tell researchers how well a material can conduct electricity. This is useful because one of the models for why Gofar behaves as it does is related to differences in the amounts of seawater present in the seafloor: fluids influence how faults stick, slide, and slip, causing earthquakes of various magnitudes. The salt in seawater makes it conduct electricity well, far better than the surrounding rocks, and so EM data provide clues as to where seawater or other fluids are hiding beneath the seafloor.

Using state of the art instruments, the study’s authors were able to create a snapshot of the electrical properties beneath the Gofar fault. They expected that one portion of the fault would be slightly more conductive than its surroundings based on prior models of such faults. Instead, the team was surprised to find that extremely conductive blobs reside beneath the seafloor on one side of the fault but not the other. To make matters more perplexing, other geophysical data from the area did not reveal similar anomalies.

“It was shocking to see such a stark contrast across the fault,” said Christine Chesley, a WHOI postdoc in Geology & Geophysics, and lead author of the study. “The conductivity structure defied all of our expectations based on what we thought we knew about oceanic transform faults.”

Oceanic transform faults have historically been thought of as simple, predictable features. They represent the least well-studied of the three major plate boundaries, which include divergent boundaries, like East Africa, where plates move apart forming new crust; and convergent boundaries, like the Himalayas, where two plates collide and recycle crust. However, recent findings like this necessitate a new framework for understanding oceanic transform faults.

“Whenever we go out and make these kinds of EM measurements, we see the seafloor through a different lens, and it almost always changes our views on the processes that shape the earth,” explained Rob Evans, Senior Scientist at WHOI in Geology & Geophysics and co-author of the study.

Determining why the conductive blobs appeared in the EM data, but did not present as other kinds of geophysical anomalies, required some deductive reasoning.

“We needed a self-consistent mechanism that could help explain why these conductive masses are existing under only one side of the fault and where seismic velocities seem unaffected,” Chesley explained. “Something with conductivities this high isn’t normally seen beneath the seafloor, except where magma is involved.”  

Working with these puzzle pieces, the authors realized that the conductive blobs required salt—a lot of salt—to account for their high conductivity values. This suggested the anomalies represented brine accumulations.

“And in order to create brines, you need a source of heat,” added Chesley. “We think this heat source is magma near the transform fault.”

The authors hypothesized that some magma is present on the side of the fault where the conductive blobs of brine are found. This would be a remarkable shift in our understanding of transform faults, which have generally not been considered to host magmatic or hydrothermal activity.

“We have this amazing image of this particular section of the Gofar fault, but we haven’t yet been able to see how it connects to the adjacent mid-ocean ridge. We are hopeful that additional project funding will support additional research,” said Evans.

The National Science Foundation’s Division of Ocean Sciences supported this project.

The following institutions contributed to this research: University of Delaware; Boise State University; ‎Scripps Institution of Oceanography, University of California San Diego; Western Washington University; University of Texas Austin; MIT-WHOI Joint Program in Oceanography/Applied Ocean Science and Engineering; University of Southern Maine; Columbia University; ‎University of New Hampshire.

About Woods Hole Oceanographic Institution

Woods Hole Oceanographic Institution (WHOI) is a private, non-profit organization on Cape Cod, Massachusetts, dedicated to marine research, engineering, and higher education. Established in 1930, its mission is to understand the ocean and its interactions with the Earth as a whole, and to communicate an understanding of the ocean’s role in the changing global environment. WHOI’s pioneering discoveries stem from an ideal combination of science and engineering—one that has made it one of the most trusted and technically advanced leaders in fundamental and applied ocean research and exploration anywhere. WHOI is known for its multidisciplinary approach, superior ship operations, and unparalleled deep-sea robotics capabilities. We play a leading role in ocean observation and operate the most extensive suite of ocean data-gathering platforms in the world. Top scientists, engineers, and students collaborate on more than 800 concurrent projects worldwide—both above and below the waves—pushing the boundaries of knowledge to inform people and policies for a healthier planet. Learn more at whoi.edu.

  

Preparing the Scripps Undersea Electromagnetic Source Instrument (SUESI) for deployment. SUESI transmits an alternating current while being deep-towed behind the ship. Ocean-bottom electromagnetometers (receivers) on the seafloor record how the signal is influenced by subsurface structures.

The seagoing science team, led by WHOI’s Rob Evans, coordinates survey logistics.

Credit

©Paige Koenig, co-author

Journal

Science Advances

DOI

10.1126/sciadv.adu3661 

Method of Research

Imaging analysis

Subject of Research

Not applicable

Article Title

Evidence for crustal brines and deep fluid infiltration in an oceanic transform fault

Article Publication Date

11-Apr-2025