Unlocking the possibilities of coffee: Physics offers a path to better brewing

The cost of the Raw Arabica Bean, the core component of most coffee, has skyrocketed in recent years due to four consecutive bad weather conditions. Climate change adds additional tension and threatens the delicate temperature balance required for the Coffea Arabica plant. This increased pressure prompted a physicist at the University of Pennsylvania to ask.

“There’s a lot of research into fluid mechanics, there’s a lot of research into particles,” says Arnold Mattizen, an assistant professor at the Faculty of Arts and Sciences. “Maybe this is one of the first studies we start putting these things together.”

Their findings published in the Journal Physics of Fluids offer a scientific approach to improving extraction efficiency, and because there is even less coffee grounds without decreasing overall quality.

“We tried to find a way to use (or) less (or) less coffee as possible. We use the liquid dynamics poured from the gooseneck kettle to increase the extraction of coffee grounds.

The experiment requires the invisible to be visible, explains Margot Young, a graduate researcher at Mathijssen Lab.

“The opacity of coffee is difficult to directly observe the dynamics pouring, so we replaced it with clear silica gel particles from glass cones,” explains Park.

The laser sheet and high-speed camera allowed the water flow to create a “miniature avalanche” of particles. This improves the internal mechanism of the flow. Water poured from height creates an avalanche effect that agitates the bed of particles and promotes extraction.

A key factor in this process is smooth and untrubrerver flow. Even with a gentle pouring stream, the gooseneck kettle is possible. “If you just use a regular water kettle, it’s a bit difficult to control where the flow goes,” says Park. “And if the flow is not layered enough, we won’t even dig into the coffee bed.”

The team discovered that water poured from height produces a stronger mixing effect.

“When you’re brewing a cup, it’s the contact between the site and the water that gets you the taste of that coffee and everything good from the site,” Young explains. “So the idea is to try to increase contact between the water and the entire site in the pour.”

They discovered that if poured from too large a height, the water stream would break down into droplets, allowing air to be carried into coffee cones, which could actually reduce the efficiency of extraction.

The researchers conducted additional experiments on real coffee grounds to measure the extraction yield of dissolved solids. Their results confirmed that coffee extraction could be adjusted by extending mixing time with a slower, more effective pouring that exploits the avalanche dynamics.

In the case of thicker water flows, they found that higher pours result in stronger coffee, confirming observations about increased agitation at height heights. When using thinner water jets, the extraction remained consistently high at various heights due to the longer pour time required to reach the target volume.

A wide range of meanings that extend beyond the kitchen

This research is a love letter to coffee and a window into the team’s broader research. “We weren’t just doing this for fun,” says Mathijssen. “We have the tools of other projects and realized that coffee could be a neat model system for exploring deeper physical principles.”

These principles extend far beyond the kitchen, says young. “The behavior of this type of liquid helps us understand how water is eroding under waterfalls and behind dams,” she says. Even wastewater treatment and filtration systems involve similar dynamics, Mathijssen adds.

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

Meanwhile, Young is using the same high-speed imaging setup to investigate how small vortices produced by pulmonary CILIA make pathogens transparent.

“You can start small, like coffee,” says Mattigesen. “And it will reveal important mechanisms on environmental or industrial scales.”