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Scientists Discover the Perfect Cup of Coffee

Japanese scientists train as baristas to find fluid thermodynamics behind the hot drink.

Science By

What’s not so hot about hot coffee —no matter how much you love it — is how quickly it cools.

Two Japanese scientists noticed that espresso has an advantage over plain coffee, in maintaining the right temperature. So they poured into some research to get to the bottom of the phenomenon. Their newly published study tells how and why espresso lets a drinker linger longer over a cuppa.

“High-quality foam plays an important role in delaying the cooling of espresso coffee,” write Yasuhiro Arii and Kaho Nishizawa, at the Department of Food Science and Nutrition at Mukogawa Women’s University, in Japan.

One can “easily deduce” this, they explain, “however, this hypothesis is not supported by experimental evidence.” So, they got some evidence.

Arii and Nishizawa were not the first to tackle this surprisingly crowded field. They gave credit, in their report, to insights gained by other scientists, about espresso.

And there were a lot of them. The very names of earlier papers seem to express, oh, a disciplined, almost sensual pleasure for this kind of research:

“Espresso Coffee: The Chemistry of Quality” (1995)

“Quality Characteristics of ‘Espresso’ Coffee. A Study Performed Through Coffee Shops” (1997)

“Influence of Extraction Temperature on the Final Quality of Espresso Coffee” (2003)

“Neglected Food Bubbles: The Espresso Coffee Foam” (2011)

“Impact of Crema on the Aroma Release and The In-Mouth Sensory Perception of Espresso Coffee” (2012)

None of those earlier investigations precisely, though, did what Arii and Nishizawa set out to do: coolly appraise the anti-cooling mechanisms of freshly produced, high-grade crema. (“Crema” is a technical name for espresso foam.)

This required hard work. Espresso only recently became popular in Japan, they explain, so these scientists, like consumers, had to scramble for their knowledge: “For the preparation of high-quality foam, the experience of a skilled barista (coffee bar technician) is required. Most scientists do not have experience as barista, and are not able to gain this experience.”

Arii and Nishizawa obtained a high-quality espresso-making machine. Then their project heated up: they toiled hard to gain experience — and reliability — at making espresso. Painstakingly, they measured temperatures, times, and volumes, and calculated both the percentage and consistency of foam.

Foam consistency got measured in a standard way, in accord with a protocol outlined in a 1997 paper by Italian espresso researchers. They scattered granulated sugar on the foam, then visually inspected the shrinkage while noting the time elapsing on a stopwatch. For temperature, they put a sensor at a particular spot inside their test cylinder.

As amateur espresso drinkers may have noticed, the amount of foam decreases “in a two-step manner: a sharp decrease followed by a gradual decrease.” The first, rapid phase typically lasts about fifteen minutes. The cooling of the liquid happens pretty much in those same two, distinct phases. There’s a well-known consequence: “The difference in temperature [after fifteen minutes] would have an effect on the palatability of espresso coffee.”

Arii and Nishizawa end their report (and I end this report, which you are reading right now, about that report) with a definitive scientific finding: “The first 15 min after extraction may be the best time to enjoy drinking espresso coffee.”