APS News

February 2020 (Volume 29, Number 2)

Brewing an Interest in Fluid Science

By Abigail Eisenstadt

Taking courses in chemical engineering and physics can be daunting for college students without a background in mathematics, but sometimes all it takes is a stimulating beverage.

In a talk titled “Teaching Fluid Dynamics with Coffee” at the 2019 APS Division of Fluid Dynamics (DFD) meeting this past November in Seattle, William Ristenpart, a professor of chemical engineering at the University of California, Davis, shared how he and his colleague Tonya Kuhl have successfully created a chemical engineering course designed for engineering novices eager to try a new field of study. They entice students to enroll in the course by using a not-so-secret ingredient: coffee.

“The main goal is to teach them that chemical engineering is a way to think about the world quantitatively by using coffee,” said Ristenpart.

Ristenpart and Kuhl first taught “The Design of Coffee” in 2013 to 18 students. In 2019, roughly 2000 students signed up to take what has become one of the most popular courses on campus. There are two versions of the class: one for engineering students and one for general education students. The general education course only requires a basic understanding of algebra, which makes it accessible for most undergraduates regardless of training.

“When you open a course up to students with tremendously different backgrounds, their quality of education is very different,” said Ristenpart. “For example, we would talk about gravitational acceleration, where fluid drains by gravity. A lot of students didn't understand ‘acceleration.’ We really had to carefully define words that we engineers take for granted.”

The first half of the general education class teaches students core principles like transport phenomena, chemical kinetics, and thermodynamics. One lesson involves reverse engineering a drip brewer, which shows how fluid mechanics principles operate inside coffee makers. The students learn how to use the conservation of mass to determine what amounts of water and coffee grounds yield exactly one kilogram of coffee—a tutorial that is helpful for the course’s final assignment.

Students also get to roast green coffee beans. Roasting catalyzes a chemical process known as the Maillard reaction, in which sugars combine with proteins and turn the beans into their familiar brown color.

Coffee class
Reeta Asmai/UC Davis College of Engineering

Coffee in the classroom

coffee beans
Reeta Asmai/UC Davis College of Engineering

The final exam is making the best coffee with the least energy.

It is important that students learn to see coffee as a colloidal fluid, stressed Ristenpart in his DFD talk. Colloids are evenly dispersed microscopic particles that cannot be filtered out of a fluid and are able to change some of the properties of that fluid. When water is poured over coffee grounds, it removes some of the soluble substances and these are left behind as colloids.

However, the concentration of colloids depends on which device filters the coffee. For example, coffee from a French press usually has more colloids because the metal mesh does not filter the particles. Coffee’s colloidal concentration affects its viscosity, which is sometimes equated as thickness. This is why French press coffee may seem sludgy, while coffee made differently may seem more watery.

After six weeks of chemical engineering fundamentals taught through grinding, roasting, and brewing coffee beans, Ristenpart and Kuhl challenge their class to complete the final design component of the course.

For the final, students compete in groups to brew one kilogram of the best-tasting coffee while using the least amount of total electrical energy. They receive a score calculated by dividing each group’s coffee taste score over their total energy consumption (measured in kilowatt hours). The winners gain “fame, glory, and bonus points,” according to Ristenpart.

As enrollment rates rose for his course, Ristenpart realized that although coffee was popular, coffee science was understudied and underfunded. So, he worked with the University of California, Davis to develop a comprehensive program committed to furthering coffee research in fields like bio-agricultural engineering, sustainability, sociology, microbiology, and—of course—chemical engineering.

“There has been close to zero academic consideration of coffee in the United States,” said Ristenpart, “... The main reason for that is that coffee is not grown here in the States, so there is no cultural or political impetus.” The UC Coffee Center is dedicated to rectifying the absence of coffee research.

Now, Ristenpart is co-director of the Coffee Center and continues to teach “The Design of Coffee.” Currently, he is collaborating with Kuhl on a third edition of their general education textbook. The two are also authoring a higher level chemical engineering textbook called “A Highly Caffeinated Introduction to Chemical Engineering.” In the future, Ristenpart wants to write a textbook for coffee industry leaders who are interested in learning more about the science behind the beloved, but deceptively simple beverage.

“In my opinion, it is actually more difficult to make a good cup of coffee than it is to make a good cup of wine,” said Ristenpart, “Coffee goes through more unit operations, processes, and steps than wine does.”

The author is the Science Communications Intern at APS.

APS encourages the redistribution of the materials included in this newspaper provided that attribution to the source is noted and the materials are not truncated or changed.

Editor: David Voss
Staff Science Writer: Leah Poffenberger
Contributing Correspondent: Alaina G. Levine
Publication Designer and Production: Nancy Bennett-Karasik

February 2020 (Volume 29, Number 2)

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Articles in this Issue
2020 APS President Philip Bucksbaum
APS Efforts to Combat Sexual Harassment in Physics
The Forum on Industrial & Applied Physics
The APS March Meeting Heads to Denver
Ending Sexual Harassment in Physics (July 17, 2019)
Brewing an Interest in Fluid Science
Mount Wilson Telescope Receives APS Historic Site Plaque
Education and Diversity News
This Month in Physics History
Office of Government Affairs
FYI: Science Policy News from AIP
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