For many of us, coffee is whatever the barista hands us in the morning or (gasp) comes out of an office Keurig. But when science turns its gaze inward at the bitter ambrosia, the results are spectacular. The fluid dynamics of spilled coffee. The physics of latte art. Have we reached the scientific pinnacle of coffee knowledge? Not even close, according to a new study.
In contrast to national espresso guidelines, the study recommends using a coarser grind and less coffee to get the most bang for your beans without sacrificing taste. The study, which was published on Wednesday in the journal Matter, mathematically modeled the process of espresso grinding before implementing their suggestions at Tailored Coffee Roasters in Eugene, Oregon.
“We're not trying to take away the art and the craft of coffee,” said Christopher Hendon, a senior author of the study and a materials chemist at the University of Oregon. “We're simply playing the supporting role, saying that once you find that beverage you like, here's an avenue for you to achieve that every time.”
The study began as a pet project that Hendon and barista Michael Cameron wanted to compile for the coffee community. The duo planned to quantify the extraction yield—a measure of coffee production commonly used by the industry—while adjusting variables like water pressure, grind setting, and mass of beans used.
Hendon and Cameron, a first author of the study, ground the beans less finely, expecting a lower yield; to their surprise, the yield increased.
“I said, ‘Well hold on, there's something physically strange happening here,’” Hendon said. “At the same time, we got started on the mathematical model, because I wanted to make sure that my sanity was intact and say that if I grind finer, I should expect higher extraction yield.”
What makes the model unique, and complicated, is its attention to detail. Senior author Jamie Foster said that the model captures the interactions between miniscule grounds of coffee, as well as the dynamics of the bed as a whole. Additionally, ground coffee comes in two sizes: boulders and fines. Too many fines can clog up the portafilter that extracts the espresso, yielding less coffee than expected.
The level of detail in the model and inclusion of pressure and espresso basket geometry distinguish this study from others that model coffee, Hendon said.
“Overall, I think honestly this might be one of the most comprehensive studies of espresso ever,” he added.
Keeping all other variables standard, the authors found that the optimal extraction point is at a coarser grind setting on the EK 43, a commercial coffee grinder; however, the study notes that baristas often use a finer setting to stretch out the time of a shot.
The Specialty Coffee Association defines espresso in part as a beverage “where the grind of coffee is such that the brew time is 20–30 seconds.” When Tailored Coffee Roasters adopted Hendon’s suggestions, though, their espresso shots routinely clocked in at 14 seconds.
“We've always been told espresso needs to be pulled for this amount of time or it's going to really affect the flavor of it,” said Brian Sung, the owner of Tailored. He added that he was excited when Hendon came to him with the idea of using less coffee and a coarser grind, since it would save the cafe money while letting baristas serve customers quicker.
In the study, Hendon and his co-authors determined that between September 2018 and 2019, Tailored saved $3,620 by using fewer beans per brew. According to Sung, the new procedure even improved the flavor of their lighter roast espresso, bringing out sweeter notes than a finer grind had.
This so-called “tasty point” is something that a barista or home brewer can determine after adjusting the way they brew espresso, Hendon said.
While Hendon is glad that he was able to include the phrase “tasty point” in a top scientific journal, he said that he was more proud of the fact that the first authors of the study were not full-time research scientists, but rather baristas.
“They're not trained scientists, but I would argue that these people who are contributing to this paper are doing science at the highest level possible—they're just doing it in a cafe setting,” he said.
Tailored just opened a second location in Eugene, and Sung said that they plan to stick with Hendon’s method to get the most grind from their grounds.
“I don't think I'll ever go back to the old way of making coffee,” Sung said.