Grinding coffee is a messy business. Static electricity builds up on the site, leaving a sticky mess in the mill. Now, a team of chemists and volcanologists from the University of Oregon has unraveled exactly how moisture affects static electricity buildup - and they've come up with a simple solution.
According to the researchers, adding a splash of water to the beans before grinding creates static electricity. It also makes for a more consistent, stronger tasting espresso.
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The new study, published in the journal Matter, may not shock avid coffee geeks, who have honed their techniques through years of intuition, experience and tips traded on online forums. For example, some baristas already use a wet teaspoon to stir coffee beans or spray a splash of water on the beans to reduce static electricity, a practice known as the "Ross Droplet Technique" or RDT. But the new paper systematically shows how moisture in coffee beans affects charge buildup and how it can be manipulated.
"The idea that you get some kind of electrical build-up in coffee grounds is a pretty old observation. If you've never seen an industrial-scale coffee roasting plant, you see coffee grounds flying up and sticking everywhere," says William Ristenpart, founding director of the Coffee Center at the University of California at Davis, who was not involved in the study. "The nice thing about this paper is that it puts some hard science and hard data behind the understanding of the mechanism."
The article also sheds more light on the burgeoning field of coffee science, which brings together experts from seemingly incongruous disciplines to conduct dozens of drinkable experiments and explore the basic science behind a cup of coffee.
One example: The new study was a collaboration between scientists interested in coffee grinding and volcanologists fascinated by the thunderstorms generated during eruptions. These scientists don't just work in different laboratories - they actually inhabit different scientific universes, publish in specialized journals and go to separate conferences.
But over coffee, the two teams realized they were studying the same core phenomenon. Whether it's a burr grinder grinding beans or an explosive eruption that pulverizes rock into ash, friction and fractures result in tiny particles that accumulate an electrical charge in the process.
While many of the details of their research are obscure to the casual coffee drinker, their article provides simple, actionable results for someone who wants to keep the kitchen tidier or for a barista who wants to make an efficient and more intense shot of espresso.
"If you're going to grind coffee from whole beans, adding a small amount of water to those whole beans before you grind them will make the coffee more accessible when you brew it," says Christopher Hendon, a coffee chemist at the University of Oregon and one of the leaders of the study.
In other words, this method "gets more coffee out of your coffee."
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Discovering common ground
The collaboration began in Hendon's coffee lab at the University of Oregon, where regular coffee hours are held.
Josh Méndez Harper, then a postdoctoral researcher in a volcanology lab, began attending the meeting as a casual coffee drinker-the kind of person who would guzzle down whatever was handed to him without thinking. But over time he became a regular customer and started to love coffee.
One day he heard Hendon and others discussing the way electricity is built up during grinding.
"I said, 'Oh! That's what I've been doing for the last five years, but in a different context,'" Méndez Harper recalls. 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 is 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 work together. Using a simple, custom-made Faraday cup machined to fit into the hopper of their coffee grinder, they set out to see if they could make similar measurements of coffee grounds.
In experiments that ranged from grinding commercially produced coffee to roasting their own beans at different levels, the team found that moisture modulated the amount of charge on coffee grounds. Lighter roasted coffees with more internal moisture acquired less static charge during grinding and tended to charge positively. Darker roasts, which are drier, took on more charge and tended to build up a negative charge.
The scientists were intrigued by the fact that coffee sometimes charged in one direction, and sometimes in the other, and that internal moisture played a key role.
"This is what no one could have foreseen," said Samo Smrke, an analytical chemist at the ZHAW University of Applied Sciences of Zurich in Switzerland, who was not involved in the work.
Smrke said one of the approaches used in the coffee industry involves a beam of charged particles called an ion beam. Sending positive or negative ions could neutralize the coffee's charge, but without knowing whether coffee will build up charge in either direction, the beam that neutralizes the charge of one type of coffee could make the charge worse for the other type of coffee. to make.
In this case, the scientists discovered that they could suppress charging altogether by simply adding external moisture - just a splash of water before grinding.
Reducing static electricity not only reduces mess, but also prevents lumps in the coffee. This means that when brewing espresso, the water reaches all the coffee grounds evenly, increasing the concentration of the final product by about 10 percent. (The brewing results do not really apply to coffee made in a French press or other brewing methods where the coffee grounds are immersed in water.)
Experts say the study is a good example of how much low-hanging scientific fruit remains in the coffee world, with opportunities to apply rigorous experimental techniques and measurements to something that many people do one or more times a day.
"There are a lot of things that just haven't been properly researched," says Chahan Yeretzian, head of the Coffee Excellence Center at ZHAW University of Applied Sciences in Zurich, who was not involved in the new research.
Josef Dufek, a volcanologist at the University of Oregon, says coffee is a fascinating model system, and he plans to apply similar techniques to understand volcanic ash. Méndez Harper sees connections with even more exotic questions. The dunes on Saturn's moon Titan, which are made of carbon-rich sand, can be similarly affected by static charge when the particles rub against each other.
But Méndez Harper is addicted to coffee. Now that he is starting his own laboratory at Portland State University, he plans to continue this multidisciplinary line of research.
"When you make a pour-over coffee, the physics there, the math, is the same that you apply to water seeping through soil or to magma moving through a porous rock matrix," Méndez Harper said. "There are a lot of parallels between coffee and earth science, beyond static generation."
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