A recent study from a team at the University of Pennsylvania proposes a small tweak to pourover brewing that maintains optimal extraction yield and flavor while requiring less coffee.
In short, the researchers suggest a higher pour with a gooseneck kettle.
Published in April in the journal Physics of Fluids, the study centers on a phenomenon called “avalanche dynamics,” through which a stream penetrates the surface of the coffee bed, then pushes and displaces grounds in a recirculating pattern. This movement allows the water to more thoroughly interact with the grounds, increasing extraction.
The coffee-water avalanche effect requires a “laminar flow” of water, described as an intense steady stream, such as that from a gooseneck kettle as opposed to a large-mouthed generic water kettle.
“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,” author Ernest Park said in an announcement of the study.
To help visualize the process, the researchers replaced coffee grounds with transparent silica gel particles in a glass funnel, using lasers and high-speed cameras to capture the mixing process. These experiments revealed that even gentle pours from a higher height produced vigorous internal movement, which remained effective even when a floating layer of grounds formed on top.
The team of physicists then repeated the tests with actual coffee grounds, measuring the extraction yield. They found that longer mixing time — achieved by pouring slowly from a higher point, yet not so high that the stream breaks up — resulted in extractions similar to lower pours on a larger coffee bed.
“If the water stream is too thin, it breaks into droplets and doesn’t mix the grounds effectively,” said study author Margot Young. “That limits the flavor and strength of the brew.”
The authors presented the research as a potential pathway towards reduced coffee consumption in the face of climate change, though the vast majority of U.S. coffee drinkers use automatic machines at home.
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