Coffee Ground With Water Makes for a More Intense Espresso

By adding a few drops of water to their coffee grinder, caffeine connoisseurs can enjoy a more intense espresso, without the side effects of static electricity. That’s according to a new paper published in Matter.

For good coffee, just add water

Grinding coffee generates static electricity, which causes the coffee particles to clump and stick to the grinder.

But does this clumping affect the taste of coffee? To find out, Christopher Hendon, a computational materials chemist at the University of Oregon, teamed up with volcanologists who study similar electrification processes during eruptions.

Together, the research team measured the amount of static produced when they ground a variety of roasted coffee beans.

They observed no association between static and the coffee’s country of origin or the beans’ processing method, but they did find associations between electrification and water content, roast color and particle size.

Crucially, the team found that less static electricity was produced when coffee had a higher internal moisture content and when it was ground at a coarser setting. Light roasts produced less charge, which was more likely to be positive, while darker roasts, which tend to be drier, charged negatively and produced more overall charge. Dark roasted coffees produced much finer particles than light roasts when ground at the same setting.

The daily grind

The researchers also tested whether grinding with water changed the way an espresso is brewed. When they compared espressos made with identical coffee beans ground either with or without a splash of water, they found that the brews from beans ground with water were stronger.

“Moisture, whether it’s residual moisture inside the roasted coffee or external moisture added during grinding, is what dictates the amount of charge that is formed during grinding,” said Hendon.

“Water not only reduces static electricity and therefore reduces mess as you’re grinding, but it can also make a major impact on the intensity of the beverage and, potentially, the ability to access higher concentrations of favorable flavors,” he added.

Grinding with water also resulted in espresso shots that were more consistent, shot to shot – a benefit many baristas might appreciate.

Heddon and his colleagues plan to follow up their study with more investigations that could benefit not just baristas, but volcanologists, too.

“It’s sort of like the start of a joke – a volcanologist and a coffee expert walk into a bar and then come out with a paper,” said Joshua Méndez Harper, a volcanologist at Portland State University and co-author of the paper. “But I think there are a lot more opportunities for this sort of collaboration, and there’s a lot more to know about how coffee breaks, how it flows as particles and how it interacts with water. These investigations may help resolve parallel issues in geophysics – whether it’s landslides, volcanic eruptions or how water percolates through soil.”

Reference: Mendez Harper J, McDonald, CS, Rheingold EJ, Kim YH, Dufek J, Hendon CH. Moisture-controlled triboelectrification during coffee grinding. Matt. 2023. doi: 10.1016/j.matt.2023.11.005

This article is a rework of a press release issued by Cell Press. Material has been edited for length and content.