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Cup of coffee
The grain size of a coffee grind plays a key role in the taste. (Credit: Starbucks)

One coffee drinker’s perfect brew may be another drinker’s battery acid, but mathematicians say they’re zeroing in on the equations behind the taste of drip coffee.

The University of Limerick’s Kevin Moroney and his colleagues lay out the state of the art in the SIAM Journal on Applied Mathematics. The findings could well spark a buzz in coffee-crazy Seattle, the birthplace of Starbucks.

“Our model describes flow and extraction in a coffee bed, specifies extraction mechanisms in terms of the coffee grain properties, and compares the model’s performance with experiment,” Moroney said in a news release from the Society for Industrial and Applied Mathematics.

One of the conclusions can be boiled down to a simple rule: If the coffee tastes too watery, grind the beans more finely. If it tastes too bitter, go with a coarser grind.

A co-author of the research paper, University of Portsmouth mathematician William Lee, says he sets his coffee grinder on the largest setting.

“The grains are a bit larger than you get in the standard grind, which makes the coffee less bitter,” he told the BBC. “Partly because it’s adjusting that trade-off between the stuff coming out of the surface and stuff coming out of the interior.”

Moroney and Lee
Researchers Kevin Moroney and William Lee measure coffee concentration using a refractometer. (Credit: University of Portsmouth)

In a follow-up email, Lee told GeekWire that the findings suggest a French-style coffee press might result in a more refined brew, “in that you have more control over the length of time the coffee spends in contact with the water.”

“Of course, the advantage of a drip filter is that it requires very little human intervention to brew coffee – something I appreciate very much early in the morning,” he wrote.

Lee said the next challenge is to study the effect of different drip methods. Is it better to pour the hot water into the center of the brewing chamber, or sprinkle it in like a shower? Are there factors that distinguish a flatbed coffeemaker from the conical variety?

“These are next on our ‘to investigate’ list,” Lee said. “We know for sure that they are important, since a single jet can deform the coffee bed by excavating the center. Our plans are to use equations developed in the context of river bed erosion to investigate this.”

Who knew the science of brewing coffee could be so complicated? It’s enough to drive a person to drink … tea.

In addition to Moroney and Lee, the authors of “Asymptotic Analysis of the Dominant Mechanisms in the Coffee Extraction Process” include Stephen O’Brien, Freek Suijver and Johan Marra. For more down-to-earth tips on brewing coffee, check out Starbucks’ online guide.

 

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