What a Volcano Scientist Figured Out About Your Coffee Grinder

If you grind beans at home, you know the mess: grounds jumping out of the cup, sticking to the chute, clumping in the corners. That’s static electricity, and one of the people who took it seriously enough to study it is a volcanologist.

Joshua Méndez Harper, of Portland State University, teamed up with University of Oregon chemist Christopher Hendon and colleagues. In December 2023 they published a study in the journal Matter about the static charge coffee builds up as it’s ground.

What they found:

• Roast matters. Darker roasts built up more charge. Lighter roasts built up less.
• Moisture matters most. Beans with more water inside them produced less static. As Hendon put it, the moisture sets how much charge you get.
• A little water helps. Adding a small amount of water to the beans before grinding cut both the static and the clumping.

The part coffee people got excited about was the espresso. With less clumping, the water pulled more out of the same amount of coffee. In the journal publisher’s press release, Hendon talked about pushing concentration up by 10 to 15 percent for the same amount of coffee, and Smithsonian Magazine, citing the Washington Post, put the boost at roughly 10 percent.

Some honest limits: the team only tested espresso. They expect a benefit for pour-over and stovetop pots too, but said immersion methods like the French press, where the grounds sit in water, aren’t expected to benefit. And “a little water” means a little, not wet beans.

A 2016 study adds a bonus. Beans ground straight from the freezer produced a more even grind, and the biggest jump in evenness came between room temperature and ordinary freezer temperature. The authors called freezer storage chemically reasonable, as long as the beans are kept away from moisture.