Research team finds a way to mass produce Dutch coffee

Dutch coffee is made by dripping cold or hot water and brewing the coffee for a long time, thus the nickname "coffee tears." Normally 12 hours is needed to get one liter, but since the time differs depending on the size of the coffee particle, which makes Dutch coffee valuable.

Professor Lee Yoon-woo of Division of Chemistry and Biology at Seoul National University and his team have recently found a way to make one liter of Dutch coffee every day, which is over 1,000 times faster than the conventional way. "We spent one year on experiments to figure out the optimal heat, pressure, time, and various factors to extracting coffee," said Professor Lee.

Lee is famous for his research on supercritical substances. A supercritical substance has two characteristics as liquid and vapor at the same time. It spreads as fast as the air and can melt other substances. For example, if supercritical carbon dioxide is sent through tiny cracks on sesame, it easily melds the oil and scent together. This is how "supercritical sesame oil" is made, which has a brighter color and tastes less bitter than common sesame oil.

The team applied this technique to the coffee beans that are used to make Dutch coffee. "The more finely beans are ground, the better the powder mixes because of a fat element called `essence oil`. We used the supercritical technique to eliminate all greasiness from the coffee beans," said the professor.

The research team ground coffee beans into particles of about 15μm (micrometer: one millionth of a meter) size. When they made Dutch coffee out of that powder, it was four to five times thicker than commercial Dutch coffee and three times thicker than espresso.

The coffee powder the team made is the same as ones used in commercial instant brewed coffee. "The powder for instant brewed coffee is made using a freeze-dry method, but the scent is lost after that," Lee said. "To preserve the scent, we inserted one to two percent of a coffee powder that we developed." The team`s coffee is used in a coffee-flavored ice cream of a famous brand.

"It was an Italian engineer who first developed the espresso machine. This shows us that coffee and science are deeply related," said the professor.

yskwon@donga.com