Mathematicians figured out the perfect espresso
People love a good cup of coffee, but how do you get the perfect brew? Short of a deep philosophical dive into the nature of perfection, an international team of mathematicians and environmental scientists believe it’s entirely possible to calculate the ideal espresso. Not only that, but they now have the formulas to back it up. The mathematics detailed in their study published in the journal Royal Society Open Science is dense. But the short answer is that it all depends on the size of the puck.
Imagine the typical espresso machine at your favorite coffee shop. The little dish your friendly barista cups the coffee grounds into is called the puck. After inserting it into the machine, hot water flows through the container and molecularly absorbs the flavor, hue, and (most importantly) caffeine from the beans.
The quality of the final espresso depends on many aspects, including how the grounds are packed, how long the water passes through the coffee, and the size of the grounds themselves. It has always been difficult to accurately predict the evolution of a cup of espresso based on these variabilities.
To get a better idea of ​​how these different factors interact, the researchers ground Tumba beans from Rwanda and Guayacán beans from Colombia into 11 sizes ranging from extremely fine to coarse. They then placed each variant in tubes before using a visualization technology called X-ray microtomography (XCT). The technique generated 3D maps of each sample’s internal structures, complete with passages between grains, called pore spaces, that are impossible to see with the human eye.
This is where the experiences started to seep in – literally. Using numerical flow tests, the team simulated the flow of water through each sample based on percolation theory, a subset of physics focused on the movement of fluids between connected spaces. The researchers were particularly interested in understanding how well each sample’s pore space facilitated the uninterrupted passage of water through the washer. Basically, they made a lot of coffee on a computer.
After comparing the results of different coffee grounds, the study authors were finally able to devise an equation that calculates how easily water permeates coffee grounds. They also concluded that the formulas were in “excellent agreement” with their theory of percolation, providing a practical way to express the size and packing of ground coffee with respect to saturation.
The main factors are the connectivity of the interstitial spaces, the grain size and surface area, and how they are compacted. All of these variables influence how long the water remains in physical contact with the coffee, thereby taking on its flavor profile. More time and contact generally means stronger flavors, and the best way to maximize this is to run as much water over the surface of the coffee grounds.
The study’s findings are less about changing your personal approach to espresso preparation and more about introducing methods to improve industrial equipment. Integrating their formulations into machine settings will allow for more personalized grinds, improved filtration, and even better brews.
In the meantime, follow your instincts. If it’s a perfect espresso for you, then that’s all that matters.
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