The science of cold-brew coffee

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Engineers design a machine to cold-brew coffee. 

Coffee pot

Students at DTU Mechanical Engineering are designing and building a machine which brews coffee that tastes even better. The secret formula is cold water and plenty of time …

Ali Gürcan Özkil loves coffee, and he drinks a lot of it. Coffee can be a hit-and-miss affair, but ten years ago he enjoyed an exceptionally good coffee experience in a San Francisco café. Not only did the coffee taste fantastic, but the coffee machine itself was also displayed as an attractive sculpture in the centre of the room.

Ali admired both the coffee and the machine, but was convinced that it had to be possible to improve the design and make the machine easier to operate. After a good deal of thought and work with a group of students on the Design and Innovation course, he is now developing the third prototype of his cold-brewing machine.

The Japanese have been enjoying ‘Kyoto cold-brew coffee’, as it is known, since the 1600s. The traditional way to prepare it involves a set-up featuring three flasks positioned one above the other. The top flask contains three litres of cold water. This oozes out through a valve at a rate of around one drip every two seconds, landing on the coffee beans in the middle flask. At the bottom stands the serving flask that catches the finished coffee. The process takes around 12 hours.

“In the Japanese system, the valve has to be adjusted manually every two hours because the pressure in the water container changes as the water runs out. And because the water container is positioned at the top of the set-up, there are limits on how large it can be—and, therefore, how much coffee you can brew at a time. Finally, it’s cumbersome to lift into position,” relates Ali.

“So we’ve chosen to place the water container at the bottom and add a pump to send the water up to the coffee beans at the perfect pace. Our design enables us to increase the volume of water to four litres or more, and to make the entire set-up a little lower.”

Cleaning and design

As mentioned above, Ali and his two BSc students—Jesper Alkestrup and Kristian Østergaard Lund—are currently working on the third prototype of their cold-brew machine. It consists of a great many parts that have to be simple to dismantle and clean every day, so that the entire machine complies with requirements from the food safety authorities.

At the same time, Ali and his team are experimenting with coffee roasters to come up with the perfect coffee, roasted and ground to provide a truly heavenly coffee experience.

“After all, there is no magic machine that can transform bad coffee into something good. And, of course, it’s all a matter of taste,” he says, adding that his coffee has been rated highly by a small focus group that especially appreciated the less bitter taste. Cold coffee is also gentler on the digestive system. Finally, if you prefer hot coffee, there is an option to make highly concentrated coffee and then simply add boiling water just before serving.

Coffee drinkers should enjoy more than ‘just’ the sublime taste, however; the machine itself should be a delight to look at, so Ali is planning to team up with a glass-blower to shape the flasks.

“It’s all about the experience for the user. The machine is a niche product that gels neatly with the current wave of enthusiasm for coffee and the emphasis on ‘slow cooking’,” he relates. Thus far, Ali has had no need to market his invention: the circle of coffee enthusiasts in the Copenhagen coffee environment is so small that rumours about the cold-brew machine are spreading like wild fire.

Ali has not yet come up with a name for his machine, and it may not have anything to do with coffee because he is already experimenting with drawing flavour out of ingredients other than coffee beans. Hop leaves, for example.

“It tastes almost like Guinness, tasty and refreshing. So why not …?”

Adapted from Article by Marianne Vang Ryde, DTU Avisen April 2016

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