by Grinding coffee is a complicated business. Static electricity builds up on the ground, leaving a sticky mass trapped in the grinder. Now, a team of chemists and volcanologists at the University of Oregon has discovered exactly how humidity affects static buildup and found a simple solution.
According to researchers, adding a splash of water to beans before grinding reduces static. It also creates a more consistent, stronger tasting shot of espresso.
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The new study, published in the journal Matter, may not surprise avid coffee fans, who have honed their techniques through years of intuition, experience and advice exchanged in online forums. Some baristas, for example, already use a wet teaspoon to stir coffee beans or spray a stream of water over the beans to reduce static, a practice known as the “Ross Drop Technique” or RDT. But the new paper systematically shows how the moisture of coffee beans affects charge buildup and how it can be manipulated.
“The idea that some kind of electrical buildup occurs in coffee grounds is a pretty old observation. If you’ve never seen an industrial-scale roaster, you can see coffee grounds flying and sticking everywhere,” said William Ristenpart. , founding director of the Coffee Center at the University of California, Davis, who was not involved in the study. “The nice thing about this paper is that it puts some science and hard data behind understanding the mechanism.”
The article also sheds more light on the burgeoning field of coffee science, which brings together experts from seemingly incongruent disciplines to conduct dozens of experiments on drinkable beverages and explore the fundamental science behind a cup of coffee.
Case in point: The new study was a partnership between scientists interested in coffee grinding and volcanologists fascinated by the thunderstorms generated during eruptions. These scientists not only work in different laboratories, but basically inhabit different scientific universes, publishing in specialized journals and attending separate conferences.
But over a cup of coffee, the two teams realized they were studying the same central phenomenon. Whether it’s a pinwheel crushing beans or an explosive eruption that pulverizes a rock to ash, friction and fractures result in tiny particles that build up electrical charge in the process.
While many of the details of his research are unknown to the casual coffee drinker, his article contains simple, practical results for a person trying to keep a tidier kitchen or a barista trying to create an efficient, stronger shot of espresso.
“If you’re grinding whole bean coffee, adding a small amount of water to those whole beans before you grind them will make the coffee more accessible when you brew it,” said Christopher Hendon, a coffee chemist at the University of Oregon and one of the study leaders.
In other words, by using this method, you “get more coffee out of your coffee.”
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Discovering common ground
The collaboration began at the Hendon Coffee Lab at the University of Oregon, which offers regular coffee hours.
Josh Mendez Harper, then a postdoctoral researcher at a volcanology lab, began attending as a casual coffee drinker: the kind of person who would swallow anything they gave him without a second thought. But over time, he became a regular and began to enjoy the coffee.
One day, he overheard Hendon and others discussing how electricity is built up during grinding.
“I said, ‘Oh! That’s what I’ve spent the last five years doing, but in a different context,'” Mendez Harper recalled. To study how charge builds up in 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 of individual particles and then calculate the density of that charge by weighing them.
The scientists decided to collaborate. Using a simple Faraday cup, custom-made and machined to fit the chute of their coffee grinder, they set out to see if they could take similar measurements of ground coffee.
In experiments ranging from grinding commercially produced coffee to roasting their own beans at different levels, the team found that humidity modulated the amount of charge in the coffee grounds. Lighter roast coffees that have more internal moisture gained less static charge during grinding and tended to become positively charged. Darker roasts, which are drier, gained more charge and tended to accumulate negative charge.
Scientists were intrigued by the fact that coffee was sometimes charged in one direction and sometimes in the other, and that internal humidity played a key role.
“This is what no one could anticipate,” said Samo Smrke, an analytical chemist at the 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 could neutralize the charge of the coffee, but without knowing whether the coffee will build up charge in either direction, the beam that neutralizes the charge of one type of coffee could make things worse for another.
In this case, the scientists found that they could suppress the charge completely simply by adding external humidity, just a splash of water before grinding.
Reducing static not only reduces mess, but also prevents lumps in your coffee. That means that when brewing espresso, the water reaches all the coffee beans evenly, increasing the concentration of the final product by about 10 percent. (The brewing results don’t really apply to coffee brewed in a French press or other brewing methods where ground beans are soaked in water.)
Experts said the study is a prime example of how much low-hanging fruit remains in the coffee world, with opportunities to apply rigorous experimental techniques and measurements to something many people do one or more times a day.
“There are a lot of things that are simply not investigated properly,” said Chahan Yeretzian, director of the Coffee Center of Excellence at ZHAW University of Applied Sciences in Zurich, who was not involved in the new study.
Josef 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. Méndez Harper sees connections to even more exotic issues. The dunes on Saturn’s moon Titan, which are made of carbon-rich sand, can be similarly influenced by static charge when the particles rub against each other.
But Méndez Harper is addicted to coffee. As he starts his own lab at Portland State University, he plans to continue this line of multidisciplinary research.
“If you make a pour-over coffee, the physics, the mathematics, are the same as those that apply to water seeping through soil or magma moving through a porous rock matrix,” Méndez Harper said. “There are many parallels beyond the static generation between coffee and earth sciences.”
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