Grinding coffee is a messy business. Static electricity builds up on the ground, leaving a sticky mess stuck in the grinder. Now, a team of chemists and volcanologists at the University of Oregon has figured out exactly how moisture affects static build-up—and they’ve come up with a simple solution.
According to the researchers, adding a splash of water to the beans before grinding reduces static electricity. It also happens to create a more consistent, stronger tasting shot of espresso.
The new study, published in the journal Matter, may not shock avid coffee geeks who have perfected their techniques through years of intuition, experience and advice traded in online forums. Some baristas, for example, already use a wet teaspoon to stir the coffee beans or spray a stream of water over the beans to reduce static electricity, a practice known as the Ross Drip Technique, or RDT. But the new paper shows systematically how moisture in coffee beans affects charge accumulation and how it can be manipulated.
“The idea that you get some kind of electrical build-up in the coffee grounds is a pretty old observation. If you’ve never seen an industrial-scale bakery, you can see coffee grounds flying up and sticking everywhere,” said William Ristenpart, founding director of the Coffee Center at UC Davis, who was not involved in the study. “What’s great about this paper is that it puts some hard science, some hard data, behind understanding the mechanism.”
The paper also sheds more light on the burgeoning field of coffee science, which brings together experts from a variety of seemingly unrelated disciplines to conduct dozens of drinking experiments and explore the fundamental science behind a cup of joe.
Case in point: The new study is a partnership between scientists interested in coffee grinding and volcanologists fascinated by the thunderstorms generated during eruptions. These scientists don’t just work in different labs — they basically inhabit different scientific universes, publishing in specialized journals and going to separate conferences.
But over a cup of coffee, the two teams realized they were studying the same basic phenomenon. Whether it’s a mill that crushes beans or an explosive eruption that pulverizes rock into ash, the friction and fractures result in tiny particles that build up an electrical charge in the process.
Although many of the details of their investigation are unclear to the average coffee drinker, their paper contains simple, practical results for a person trying to maintain a tidier kitchen, or a barista trying to create an efficient and more intense brew espresso.
“If you’re going to grind whole-bean coffee, adding a small amount of water to those whole beans before you grind them will result in a more accessible coffee when you brew it,” said Christopher Hendon, a coffee chemist at the University of Oregon and one of the study leaders.
In other words, using this method, “you get more coffee out of your coffee.”
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The collaboration began at the Hendon Coffee Lab at the University of Oregon, where regular coffee classes are held.
Josh Mendez Harper, then a postdoctoral fellow in a volcanology lab, started attending as a casual coffee drinker—the kind of guy who would gobble up whatever was handed to him without a second thought. But over time he became a regular visitor and started drinking coffee.
One day he overheard Hendon and others discussing how electricity was built up during grinding.
“I said, ‘Oh! That’s what I’ve been doing for the last five years, but in a different context,” Mendes Harper recalled. To study how charge builds up on volcanic ash, volcanologists sometimes use a device called a Faraday cup. Despite the name, it has nothing to do with drinking – it’s a conductive metal cup, and scientists can use it to measure the charge on individual particles, then calculate the density of that charge by weighing them.
The scientists decided to collaborate. Using a simple, custom-made Faraday cup that had been machined to fit the chute of their coffee grinder, they set out to see if they could make similar measurements on coffee grounds.
In experiments that ranged from grinding commercially produced coffee to roasting their own beans to varying degrees, the team found that moisture modulates the amount of charge in the coffee grounds. Lighter roast coffees, which have more internal moisture, acquire less static charge during grinding and tend to become positively charged. Darker roasts, which are drier, gain more charge and tend to accumulate a negative charge.
The scientists were intrigued that the coffee sometimes loaded in one direction and sometimes the other, and that internal moisture played a key role.
“This is what no one could have predicted,” said Samo Smrke, an analytical chemist at ZHAW Zurich University of Applied Sciences in Switzerland, who was not involved in the work.
Smrke said one approach used in the coffee industry involves a beam of charged particles called an ion beam. Sending positive or negative ions can neutralize the coffee’s charge, but without knowing whether the coffee will build up a charge in either direction, a beam that neutralizes the charge on one type of coffee can make it worse for another.
In this case, the scientists found they could completely suppress charging simply by adding external moisture—just a spray of water before grinding.
Reducing static electricity not only reduces mess, but also avoids lumps in the coffee. This means that when you make an espresso, the water reaches the entire coffee grounds evenly, increasing the concentration of the final product by about 10 percent. (Brewing results do not actually apply to coffee made in a French press or other brewing methods where the grounds are immersed in water.)
Experts said the study is a prime example of how much low-hanging scientific fruit remains in the world of coffee, with opportunities to bring rigorous experimental techniques and measurements to something many people do one – or more – times a day.
“There are a lot of things that just haven’t been properly studied,” said Chahan Yeretzian, head of the Coffee Center of Excellence at ZHAW Zurich University of Applied Sciences, who was not involved in the new study.
Joseph Dufek, a volcanologist at the University of Oregon, says coffee is a fascinating model system, and he plans to apply similar techniques to try to understand volcanic ash. Mendes Harper sees connections to even more exotic issues. The dunes on Saturn’s moon Titan, which are made of carbon-rich sand, may be similarly affected by static charging as the particles rub against each other.
But Mendes Harper is addicted to coffee. As he starts his own lab at Portland State University, he plans to continue this multidisciplinary line of research.
“If you brew coffee, the physics there, the math, is the same that you apply to water percolating through soil or magma moving through a porous rock matrix,” Mendes Harper said. “There are many parallels beyond static generation between coffee and the earth sciences.”