EUGENE, Ore. - Jan. 22, 2020 - Espresso delivers a desired jolt of caffeine but getting a consistent good-taste is difficult. New research is offering a roadmap to reproducibility and a potential savings of $3.1 million a day for coffee shops across the United States.
In a new study, now online ahead of print in the journal Matter, a 10-member international team of researchers performed mathematical modeling and brewed hundreds of espresso shots to discover the key variables required to make consistently tasty coffee.
The general conclusions: Use less coffee at a courser grind than traditionally recommended, and brew it faster using less water than current practices.
That approach, the team concluded, reduces the amount of coffee used in espresso by 25 percent, saves coffee shops 13 cents per espresso-based drink and could make the industry more sustainable by reducing waste.
In the United States, alone, 124 million espresso-based drinks are consumed daily. From each bag of beans, a buyer realizes only about 18 to 22 percent of the mass getting into their coffee.
The approached gleaned from the research would allow extraction yields above that 22 percent level, said co-author Christopher H. Hendon, a chemist at the University of Oregon.
"We want to extract more from the coffee to save money, and be sustainable, but we also want it to taste delicious, not burnt or bitter," he said. "Our method allows us to push extractions and have the shots taste great, while being more sustainable and saving money."
And that, he said, would benefit the industry.
"For the local shop owner, this is an opportunity to save a lot of money without sacrificing quality," he said. "For the roaster, this is an opportunity to reflect on the approach to roasting and how people are brewing their coffee. For the producer, this should encourage them continue to produce high-quality coffee that can earn them the most money, knowing that more people will have access to it."
The research team - chemists, mathematicians and coffee professionals from five countries - analyzed grind size, water pressure, flow rate, amount of coffee and extraction kinetics to seek an optimum extraction yield - the percentage of coffee that gets into a shot of espresso. The recipe that emerged from the experiments, done in Brisbane, Australia, were tested in a Eugene coffee shop.
"The real impact of this paper is that the most reproducible thing you can do is use less coffee," Hendon said. "If you use 15 grams instead of 20 grams of coffee and grind your beans coarser, you end up with a shot that runs really fast but tastes great. Instead of taking 25 seconds, it could run in 7 to 14 seconds. But you end up extracting more positive flavors from the beans, so the strength of the cup is not dramatically reduced. Bitter, off-tasting flavors never have a chance to make their way into the cup."
The key to improving espresso reproducibility, Hendon said, is to determine which grind setting enables a maximum extraction from the coffee, and still tastes good.
In practice though, Hendon said, baristas typically find a grind setting on their equipment that produces the most concentrated, reproducible coffee, then modify the mass of water being used. That usually involves a reduction in shot volume to get a desired flavor. However, if the volume is too small, he said, an operator should grind coarser and repeat the volume-reduction process to reach a bigger drink of lower concentration but reproducibly tasty.
"Our model lets us take the leap from a very small particle size, less than the size of a hair, and solve a series of equations that tell us how much mass can be transported out of these little particles," said co-author Jamie M. Foster of the School of Mathematics and Physics at the University of Portsmouth in the United Kingdom.
In their modeling, the researchers drew on electrochemistry, likening how caffeine and other molecules dissolve out of coffee grounds to how lithium ions move through the electrodes of a battery. Borrowing modeling methodologies from battery work led to a rigorous coffee extraction model capable of making powerful and testable predictions.
Fine-tuning that formula for consumers, including those who brew their own espresso at home, however, requires human taste preferences to identify a sweet spot of consistent taste, which can vary from person to person and coffee to coffee, Hendon said. Baristas and home connoisseurs will need to use their judgment and experiment with their grinder and coffee-shop recipes to obtain consistent results.
"A good espresso beverage can be made in a multitude of ways," he said. "The point of this paper was to give people a map for making an espresso beverage that they like and then be able to make it 100 times in a row."
Co-authors with Hendon and Foster were: Michael I. Cameron and Dechen Morisco of Frisky Goat Espresso in Brisbane, Australia; Daniel Hofstetter of Daniel Hofstetter Performance in Switzerland; Erol Uman of Metrics Ltd., U.K.; Justin Wilkinson of the University of Cambridge, U.K.; Zachary C. Kennedy of the Pacific Northwest Laboratory in Richland, Washingon; Sean A. Fontenot, currently a research associate in the UO's Materials Science Institute; and William T. Lee of the University of Huddersfield, U.K., and University of Limerick in Ireland.
Barista Technology BV and Acaia Corp. donated equipment for the project. Testing was done at Tailored Coffee Roasters in Eugene. Computations done by the researchers were done collaboratively via the Extreme Science and Engineering Discovery Environment - a virtual system of shared computing resources, data and expertise supported by the National Science Foundation.
Source: Christopher Hendon, assistant professor, UO Department of Chemistry and Biochemistry, 541-346-2637, firstname.lastname@example.org
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