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Brewing coffee is an integral part of daily life for many, but enhancing your cup doesn’t have to come with a hefty price tag. A new study by researchers at the University of Pennsylvania, published on April 8 in Physics of Fluids, highlights that a fundamental grasp of the pour-over method’s interplay of molecular chemistry, physics, and fluid dynamics can significantly enhance coffee quality without breaking the bank.
To delve into the intricate interactions that occur during pour-over brewing, the researchers utilized silica gel particles instead of traditional coffee grounds within a transparent cone. By employing a laser sheet and a high-speed camera, they meticulously observed the response of fine-grained materials like coffee to water poured from a standard gooseneck kettle, varying the height and intensity of the pour.
The findings underscored that achieving the optimal pour-over coffee necessitates inducing an ‘avalanche effect’ among the grains, which is best accomplished through a careful combination of height and pouring intensity.
Study co-author Ernest Park provided clarity on their findings, suggesting, “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.” This steady stream poured from an elevated height allows the coffee grounds to shift and circulate effectively as water permeates deeper into the coffee bed.
Interestingly, while this technique often results in a layer of floating particles on the water’s surface, the researchers found that it does not significantly hinder mixing quality. Conversely, a pour that is too weak or too shallow can detrimentally affect the brewing process.
“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,” added Margot Young, another co-author of the study.
The researchers conclude that the efficiency of extracting the desirable flavors from the coffee can be optimized by prolonging the mixing time through slower, yet more effective pours, utilizing the principles of avalanche dynamics.
Incorporating this strategy not only elevates the quality of the coffee but also contributes to sustainability. The coffee industry, which sees consumption in the tens of billions of pounds yearly, faces challenges due to climate change affecting major coffee-growing regions like Ethiopia and Brazil. The technique proposed by Park and Young promotes a more flavorful brew while using fewer beans.
“Instead of increasing the amount of beans, the sensory profile and the strength of the beverage can be adjusted by varying the flow rate and the pour height,” they emphasize. “This way, the extraction efficiency could be better controlled to help alleviate the demand on coffee beans worldwide.”
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