What’s the best way to brew strong pour-over coffee?

By Stephen Beech

The optimal way to brew strong pour-over coffee with minimal grinds has been identified by scientists.

Millions of cups of coffee are drunk around the world every day.

But scientists say that, due to its very specific agricultural needs, it can be difficult to cultivate, and climate change threatens its growth.

To efficiently meet the high demand for coffee grounds, researchers from the University of Pennsylvania in the United States worked to optimize their use in pour-over coffee.

Study co-author Ernest Park said: “What we recommend is making the pour height as high as possible, while still maintaining a laminar flow, where the jet doesn’t break up when it impacts the coffee grinds."

The research team's findings show that the thick water jets typical of standard gooseneck kettles are "ideal" for achieving the necessary height and laminar flow.

Strong - but focused - water jets create an "avalanche" in the coffee grounds, according to the research published in the journal Physics of Fluids.

The researchers explained that displaced grounds recirculate as the water digs deeper into the coffee bed, allowing for better mixing between the water and the grounds, resulting in a stronger coffee with fewer beans.

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But if the water jet is too thin, it can't adequately create that interaction to achieve a desirable strength and sensory experience.

Co-author Margot Young, also a PhD student, said: “If you have a thin jet, then it tends to break up into droplets.

“That’s what you want to avoid in these pour-overs because that means the jet cannot mix the coffee grounds effectively.”

The researchers said that the dark color of coffee beans - and of coffee itself - makes it hard to demystify.

Along with creating pour-over drinks with actual coffee grounds, the team supplemented their study with laser-illuminated transparent particles in a glass funnel to help thoroughly visualize the mixing dynamics and understand how the liquid jet affects the grains.

They say there are many other parameters left to explore, such as the impacts of the size of the coffee grounds on the interplay between the physics and chemistry of the brewing process.

Study senior author Dr. Arnold Mathijssen added: “We can really learn something from both the chemistry and physics point of view by looking at the kitchen.

“It leads to new science where you didn’t expect it.”