University of Oregon: Electricity makes coffee & volcanic ash clumpy so just add water



(The Center Square) – New University of Oregon research found that adding a squirt of water to coffee beans before grinding cuts down on static electric charge on the coffee grounds.

The reduced microscopic clumping of the grounds during brewing ensures water moves through the packed grounds in a more even and thorough manner.

“For brew methods like espresso, having consistent flow is a good thing,” UO chemist and study co-author Christopher Hendon, known as Dr. Coffee, said.

Doing it reduces variability from cup to cup and allows baristas to use slightly less coffee since less gets left behind.

It could increase profitability by reducing waste while saving home brewers and industrial-scale coffee producers money, the report said.

“We didn’t know how much charge accumulated on coffee and that it depended on water content,” Hendon said. “That’s powerful because it means you could turn charging on and off.”

The idea came about because Hendon’s coffee lab hosts regular coffee hours for the Eugene campus community.

Volcanologists Josef Dufek and Josh Méndez Harper often attended these events. While at the coffee bar, the two saw similarities between coffee and the plumes of volcanic ash, magma, and water they typically study.

“Coffee provides a nice platform to explore particle-scale physics that occur in volcanic plumes but are obviously very difficult to study directly in nature,” Méndez Harper, a former project engineer in Dufek’s lab, said.

In both instances, materials in different states of matter interact with one another. However, coffee is less dangerous than magma, making studying it easier.

In a paper three years ago, Hendon’s team found coffee forms microscopic clumps, particularly at the fine grind level.

“While invisible to the naked eye, those clumps decrease the extraction yield of the coffee,” a release said. “That is, the water doesn’t touch every coffee ground evenly, resulting in wasted material and cup-to-cup variability.”

Hendon’s lab wanted to find out why those clumps form and how to eliminate them. He thought static electricity may be a culprit.

Though some baristas add a squirt of water before grinding to cut static, something known as the Ross droplet technique, nobody had measured the charge on coffee specifically or looked at how it may vary with different types of coffee.

By working with Dufek and Méndez Harper, Hendon’s team repurposed a tool used to measure electric charges on wildfire and volcanic ash.

They ground coffee above the instrument, a small metal vessel called a Faraday cup. They then collected coffee particles falling into it. These charged particles produce measurable currents when they enter the cup.

“The larger the charge on the particles, the larger the current,” the release said.

Along with a team of undergraduate and graduate student researchers, they tested many different types of coffee, roasting levels, and grind sizes to see how different variables impacted the charge.

One of the things that made a difference was the internal moisture of the beans.

The clumping issue was more prevalent with dark roast coffees, the release said.

“Dark roast coffees tend to have less moisture because they’re usually roasted longer,” the release said. “Also, dark roasts tended to have a negative charge, whereas lighter roasts — which have more residual moisture — acquired a positive charge.”

Adding a splash of water pre-grind eliminated the static charge and cut down on the clumping effects, the release said. It also got them a 10% higher yield from the coffee.

“Some baristas may have already anecdotally arrived at our conclusions; it’s validating some industry know-how,” Hendon said. “We are advocating for yet another step in producing excellent quality coffee, but it turns out you can’t cut corners if you want to achieve excellence.”

The static comes from the rubbing and crackling of coffee beans against the burrs of the grinder, Hendon thinks. However, since the internal moisture content of the beans influences it, this is something roasters might be able to control for by adjusting the roasting temperature and time.

Dufek and Méndez Harper think these findings could help their research on volcanoes.

“How particles break, or fragment, is one of the leading controls on eruption behavior; grinding roasted coffee is a way to explore the physics of fracture,” the release said.

Similar to coffee, volcanic ash particles are sometimes highly charged. It can result in volcanic lightning storms and also influence the length volcanic ash stays in the air and the distance it travels after an eruption.

Water also plays a role in volcanic eruptions, as it does in making coffee.

“Explosive volcanoes have a lot of water vapor that helps drive and shape the eruptions,” Dufek said.

“Ultimately, this project really shows the value of community efforts,” he added. “A coffee hour where people gather provides time and space to think about what’s convergent with research.”

The coffee market is an $11 billion industry in the United States. It is expected to grow 3.21% annually between 2023 and 2028, according to Statista.

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