When it comes to coffee, a little bit can go a long way – with the help of physics. That’s what researchers from the University of Pennsylvania recently discovered, according to a new study published this week in the Physics of Fluids journal.
“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,” explained co-author Ernest Park, a graduate researcher in the Mathijssen Lab.
For those unfamiliar with the gooseneck kettle, it is an appliance used for making hot beverages such as coffee and tea. Food & Wine said in a January article that it is actually the ideal appliance for “better brews and more precise pours.”
These kettles have long, narrow spouts that produce a thin, steady stream of water that pours slowly, without uneven splashing. With this slow pour, tea and coffee grounds saturate more evenly.
Park and other researchers who contributed to the recent study were interested in maximizing the potential of coffee beans due to concerns about the availability of those Coffea arabica beans. According to a press release from the university, four consecutive seasons of adverse weather have contributed to a spike in bean costs and climate change has added further strain on supply.
“There’s a lot of research on fluid mechanics, and there’s a lot of research on particles separately,” said 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.”
A gooseneck kettle was important to this research because it required a process called “laminar,” or a smooth flow. They used the kettle and transparent silica gel particles in a glass cone for their research. Coffee’s opacity can make studying it challenging, and transparent silica helped the researchers observe fluid dynamics more thoroughly.
“A laser sheet and high-speed camera allowed them to watch water streams create ‘miniature avalanches’ of particles—revealing the flow’s inner workings,” the university said. “Water poured from a height produces the avalanche effect that stirs the bed of particles and enhances extraction.”
As they observed this process, the researchers discovered that height matters. Liquid poured from a greater height actually created 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,” said co-author Margot Young, a graduate researcher in the Mathijssen Lab. “So, the idea is to try to increase the contact between the water and the grounds overall in the pour-over.”
However, they found that going too high can also ruin things. At a certain height, the water stream breaks apart into droplets. Those bring air into the coffee cone and that can decrease extraction efficiency. Experiments with real coffee grounds confirmed that coffee extraction can be tuned by extending mixing time and utilizing 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,” said the University of Pennsylvania. It described the research as a “love letter to coffee.”
Previously, Audacy has reported on the potential health benefits of coffee – including possibly adding up to two years to people’s lives – as well as coffee staple Starbucks’ shrinking menu. We’ve also highlighted some other coffee chains that consumers might find more affordable.
Young said the research team’s findings also apply to more than just pouring better, more sustainable cups of joe. This research also helps scientists understand how water erodes rock under waterfalls or behind dams, wastewater treatment and filtration and more.
“You can start small, like with coffee,” Mathijssen said. “And end up uncovering mechanisms that matter at environmental or industrial scales.”